| Message ID | 20191220232810.GA20233@ircssh-2.c.rugged-nimbus-611.internal (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add pidfd_getfd syscall | expand |
On 2019-12-20, Sargun Dhillon <sargun@sargun.me> wrote: > This syscall allows for the retrieval of file descriptors from other > processes, based on their pidfd. This is possible using ptrace, and > injection of parasitic code along with using SCM_RIGHTS to move > file descriptors between a tracee and a tracer. Unfortunately, ptrace > comes with a high cost of requiring the process to be stopped, and > breaks debuggers. This does not require stopping the process under > manipulation. > > One reason to use this is to allow sandboxers to take actions on file > descriptors on the behalf of another process. For example, this can be > combined with seccomp-bpf's user notification to do on-demand fd > extraction and take privileged actions. For example, it can be used > to bind a socket to a privileged port. > > /* prototype */ > /* > * pidfd_getfd_options is an extensible struct which can have options > * added to it. If options is NULL, size, and it will be ignored be > * ignored, otherwise, size should be set to sizeof(*options). If > * option is newer than the current kernel version, E2BIG will be > * returned. > */ > struct pidfd_getfd_options {}; > long pidfd_getfd(int pidfd, int fd, unsigned int flags, > struct pidfd_getfd_options *options, size_t size); > > /* testing */ > Ran self-test suite on x86_64 > > Signed-off-by: Sargun Dhillon <sargun@sargun.me> > --- > MAINTAINERS | 1 + > arch/alpha/kernel/syscalls/syscall.tbl | 1 + > arch/arm/tools/syscall.tbl | 1 + > arch/arm64/include/asm/unistd.h | 2 +- > arch/arm64/include/asm/unistd32.h | 2 + > arch/ia64/kernel/syscalls/syscall.tbl | 1 + > arch/m68k/kernel/syscalls/syscall.tbl | 1 + > arch/microblaze/kernel/syscalls/syscall.tbl | 1 + > arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + > arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + > arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + > arch/parisc/kernel/syscalls/syscall.tbl | 1 + > arch/powerpc/kernel/syscalls/syscall.tbl | 1 + > arch/s390/kernel/syscalls/syscall.tbl | 1 + > arch/sh/kernel/syscalls/syscall.tbl | 1 + > arch/sparc/kernel/syscalls/syscall.tbl | 1 + > arch/x86/entry/syscalls/syscall_32.tbl | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > arch/xtensa/kernel/syscalls/syscall.tbl | 1 + > include/linux/syscalls.h | 4 + > include/uapi/asm-generic/unistd.h | 3 +- > include/uapi/linux/pidfd.h | 10 ++ > kernel/pid.c | 115 ++++++++++++++++++++ > 23 files changed, 151 insertions(+), 2 deletions(-) > create mode 100644 include/uapi/linux/pidfd.h > > diff --git a/MAINTAINERS b/MAINTAINERS > index cc0a4a8ae06a..bc370ff59dbf 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -13014,6 +13014,7 @@ M: Christian Brauner <christian@brauner.io> > L: linux-kernel@vger.kernel.org > S: Maintained > T: git git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git > +F: include/uapi/linux/pidfd.h > F: samples/pidfd/ > F: tools/testing/selftests/pidfd/ > F: tools/testing/selftests/clone3/ > diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl > index 8e13b0b2928d..d1cac0d657b7 100644 > --- a/arch/alpha/kernel/syscalls/syscall.tbl > +++ b/arch/alpha/kernel/syscalls/syscall.tbl > @@ -475,3 +475,4 @@ > 543 common fspick sys_fspick > 544 common pidfd_open sys_pidfd_open > # 545 reserved for clone3 > +548 common pidfd_getfd sys_pidfd > diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl > index 6da7dc4d79cc..ba045e2f3a60 100644 > --- a/arch/arm/tools/syscall.tbl > +++ b/arch/arm/tools/syscall.tbl > @@ -449,3 +449,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h > index 2629a68b8724..b722e47377a5 100644 > --- a/arch/arm64/include/asm/unistd.h > +++ b/arch/arm64/include/asm/unistd.h > @@ -38,7 +38,7 @@ > #define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5) > #define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800) > > -#define __NR_compat_syscalls 436 > +#define __NR_compat_syscalls 439 > #endif > > #define __ARCH_WANT_SYS_CLONE > diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h > index 94ab29cf4f00..a8da97a2de41 100644 > --- a/arch/arm64/include/asm/unistd32.h > +++ b/arch/arm64/include/asm/unistd32.h > @@ -879,6 +879,8 @@ __SYSCALL(__NR_fspick, sys_fspick) > __SYSCALL(__NR_pidfd_open, sys_pidfd_open) > #define __NR_clone3 435 > __SYSCALL(__NR_clone3, sys_clone3) > +#define __NR_pidfd_getfd 438 > +__SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd) > > /* > * Please add new compat syscalls above this comment and update > diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl > index 36d5faf4c86c..2b11adfc860c 100644 > --- a/arch/ia64/kernel/syscalls/syscall.tbl > +++ b/arch/ia64/kernel/syscalls/syscall.tbl > @@ -356,3 +356,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > # 435 reserved for clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl > index a88a285a0e5f..44e879e98459 100644 > --- a/arch/m68k/kernel/syscalls/syscall.tbl > +++ b/arch/m68k/kernel/syscalls/syscall.tbl > @@ -435,3 +435,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > # 435 reserved for clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl > index 09b0cd7dab0a..7afa00125cc4 100644 > --- a/arch/microblaze/kernel/syscalls/syscall.tbl > +++ b/arch/microblaze/kernel/syscalls/syscall.tbl > @@ -441,3 +441,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl > index e7c5ab38e403..856d5ba34461 100644 > --- a/arch/mips/kernel/syscalls/syscall_n32.tbl > +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl > @@ -374,3 +374,4 @@ > 433 n32 fspick sys_fspick > 434 n32 pidfd_open sys_pidfd_open > 435 n32 clone3 __sys_clone3 > +438 n32 pidfd_getfd sys_pidfd_getfd > diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl > index 13cd66581f3b..2db6075352f3 100644 > --- a/arch/mips/kernel/syscalls/syscall_n64.tbl > +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl > @@ -350,3 +350,4 @@ > 433 n64 fspick sys_fspick > 434 n64 pidfd_open sys_pidfd_open > 435 n64 clone3 __sys_clone3 > +438 n64 pidfd_getfd sys_pidfd_getfd > diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl > index 353539ea4140..e9f9d4a9b105 100644 > --- a/arch/mips/kernel/syscalls/syscall_o32.tbl > +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl > @@ -423,3 +423,4 @@ > 433 o32 fspick sys_fspick > 434 o32 pidfd_open sys_pidfd_open > 435 o32 clone3 __sys_clone3 > +438 o32 pidfd_getfd sys_pidfd_getfd > diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl > index 285ff516150c..c58c7eb144ca 100644 > --- a/arch/parisc/kernel/syscalls/syscall.tbl > +++ b/arch/parisc/kernel/syscalls/syscall.tbl > @@ -433,3 +433,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3_wrapper > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl > index 43f736ed47f2..707609bfe3ea 100644 > --- a/arch/powerpc/kernel/syscalls/syscall.tbl > +++ b/arch/powerpc/kernel/syscalls/syscall.tbl > @@ -517,3 +517,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 nospu clone3 ppc_clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl > index 3054e9c035a3..185cd624face 100644 > --- a/arch/s390/kernel/syscalls/syscall.tbl > +++ b/arch/s390/kernel/syscalls/syscall.tbl > @@ -438,3 +438,4 @@ > 433 common fspick sys_fspick sys_fspick > 434 common pidfd_open sys_pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3 sys_clone3 > +438 common pidfd_getfd sys_pidfd_getfd sys_pidfd_getfd > diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl > index b5ed26c4c005..88f90895aad8 100644 > --- a/arch/sh/kernel/syscalls/syscall.tbl > +++ b/arch/sh/kernel/syscalls/syscall.tbl > @@ -438,3 +438,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > # 435 reserved for clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl > index 8c8cc7537fb2..218df6a2326e 100644 > --- a/arch/sparc/kernel/syscalls/syscall.tbl > +++ b/arch/sparc/kernel/syscalls/syscall.tbl > @@ -481,3 +481,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > # 435 reserved for clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl > index 15908eb9b17e..9c3101b65e0f 100644 > --- a/arch/x86/entry/syscalls/syscall_32.tbl > +++ b/arch/x86/entry/syscalls/syscall_32.tbl > @@ -440,3 +440,4 @@ > 433 i386 fspick sys_fspick __ia32_sys_fspick > 434 i386 pidfd_open sys_pidfd_open __ia32_sys_pidfd_open > 435 i386 clone3 sys_clone3 __ia32_sys_clone3 > +438 i386 pidfd_getfd sys_pidfd_getfd __ia32_sys_pidfd_getfd > diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl > index c29976eca4a8..cef85db75a62 100644 > --- a/arch/x86/entry/syscalls/syscall_64.tbl > +++ b/arch/x86/entry/syscalls/syscall_64.tbl > @@ -357,6 +357,7 @@ > 433 common fspick __x64_sys_fspick > 434 common pidfd_open __x64_sys_pidfd_open > 435 common clone3 __x64_sys_clone3/ptregs > +438 common pidfd_getfd __x64_sys_pidfd_getfd > > # > # x32-specific system call numbers start at 512 to avoid cache impact > diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl > index 25f4de729a6d..ae15183def12 100644 > --- a/arch/xtensa/kernel/syscalls/syscall.tbl > +++ b/arch/xtensa/kernel/syscalls/syscall.tbl > @@ -406,3 +406,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h > index 2960dedcfde8..62fe706329d1 100644 > --- a/include/linux/syscalls.h > +++ b/include/linux/syscalls.h > @@ -69,6 +69,7 @@ struct rseq; > union bpf_attr; > struct io_uring_params; > struct clone_args; > +struct pidfd_getfd_options; > > #include <linux/types.h> > #include <linux/aio_abi.h> > @@ -1000,6 +1001,9 @@ asmlinkage long sys_fspick(int dfd, const char __user *path, unsigned int flags) > asmlinkage long sys_pidfd_send_signal(int pidfd, int sig, > siginfo_t __user *info, > unsigned int flags); > +asmlinkage long sys_pidfd_getfd(int pidfd, int fd, > + struct pidfd_getfd_options __user *options, > + size_t, usize); > > /* > * Architecture-specific system calls > diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h > index 1fc8faa6e973..f358488366f6 100644 > --- a/include/uapi/asm-generic/unistd.h > +++ b/include/uapi/asm-generic/unistd.h > @@ -850,9 +850,10 @@ __SYSCALL(__NR_pidfd_open, sys_pidfd_open) > #define __NR_clone3 435 > __SYSCALL(__NR_clone3, sys_clone3) > #endif > +#define __NR_pidfd_getfd 438 > > #undef __NR_syscalls > -#define __NR_syscalls 436 > +#define __NR_syscalls 439 > > /* > * 32 bit systems traditionally used different > diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h > new file mode 100644 > index 000000000000..0a3fc922661d > --- /dev/null > +++ b/include/uapi/linux/pidfd.h > @@ -0,0 +1,10 @@ > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ > +#ifndef _UAPI_LINUX_PIDFD_H > +#define _UAPI_LINUX_PIDFD_H > + > +struct pidfd_getfd_options {}; Are empty structs well-defined in C (from memory, some compilers make them non-zero in size)? Since we probably plan to add a flags field in the future anyway, why not just have a __u64 flags which must be zeroed? > + > +#define PIDFD_GETFD_OPTIONS_SIZE_VER0 0 > +#define PIDFD_GETFD_OPTIONS_SIZE_LATEST PIDFD_GETFD_OPTIONS_SIZE_VER0 > + > +#endif /* _UAPI_LINUX_PIDFD_H */ > diff --git a/kernel/pid.c b/kernel/pid.c > index 2278e249141d..2a9cb4be383f 100644 > --- a/kernel/pid.c > +++ b/kernel/pid.c > @@ -42,6 +42,7 @@ > #include <linux/sched/signal.h> > #include <linux/sched/task.h> > #include <linux/idr.h> > +#include <uapi/linux/pidfd.h> > > struct pid init_struct_pid = { > .count = REFCOUNT_INIT(1), > @@ -578,3 +579,117 @@ void __init pid_idr_init(void) > init_pid_ns.pid_cachep = KMEM_CACHE(pid, > SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT); > } > + > +static struct file *__pidfd_getfd_fget_task(struct task_struct *task, u32 fd) > +{ > + struct file *file; > + int ret; > + > + ret = mutex_lock_killable(&task->signal->cred_guard_mutex); > + if (ret) > + return ERR_PTR(ret); > + > + if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS)) { > + file = ERR_PTR(-EPERM); > + goto out; > + } > + > + file = fget_task(task, fd); > + if (!file) > + file = ERR_PTR(-EBADF); > + > +out: > + mutex_unlock(&task->signal->cred_guard_mutex); > + return file; > +} > + > +static long pidfd_getfd(struct pid *pid, u32 fd) > +{ > + struct task_struct *task; > + struct file *file; > + int ret, retfd; > + > + task = get_pid_task(pid, PIDTYPE_PID); > + if (!task) > + return -ESRCH; > + > + file = __pidfd_getfd_fget_task(task, fd); > + put_task_struct(task); > + if (IS_ERR(file)) > + return PTR_ERR(file); > + > + retfd = get_unused_fd_flags(O_CLOEXEC); > + if (retfd < 0) { > + ret = retfd; > + goto out; > + } > + > + /* > + * security_file_receive must come last since it may have side effects > + * and cannot be reversed. > + */ > + ret = security_file_receive(file); > + if (ret) > + goto out_put_fd; > + > + fd_install(retfd, file); > + return retfd; > + > +out_put_fd: > + put_unused_fd(retfd); > +out: > + fput(file); > + return ret; > +} > + > +/** > + * sys_pidfd_getfd() - Get a file descriptor from another process > + * > + * @pidfd: file descriptor of the process > + * @fd: the file descriptor number to get > + * @options: options on how to get the fd > + * @usize: the size of options > + * > + * This syscall requires that the process has the ability to ptrace the > + * process represented by the pidfd. It will return a duplicated version > + * of the file descriptor on success. The process who which is having > + * its file descriptor taken is otherwise unaffected. If options is NULL > + * it is ignored along with usize. > + * > + * Return: On success, a file descriptor with cloexec is returned. > + * On error, a negative errno number will be returned. > + */ > +SYSCALL_DEFINE4(pidfd_getfd, int, pidfd, int, fd, > + struct pidfd_getfd_options __user *, options, size_t, usize) > +{ > + struct pid *pid; > + struct fd f; > + int ret; > + > + BUILD_BUG_ON(sizeof(struct pidfd_getfd_options) != PIDFD_GETFD_OPTIONS_SIZE_LATEST); > + > + /* > + * options is currently unused, verify it's unset or if it is set, > + * ensure that size is 0. > + * > + * In the future, this will need to adopt copy_struct_from_user. > + */ > + if (options && usize > PIDFD_GETFD_OPTIONS_SIZE_VER0) > + return -E2BIG; I wouldn't suggest doing this. I understand that this is simpler, but it will cause problems once we add a field to pidfd_getfd_options -- newer programs compiled with a larger struct won't work on older kernels with this check (even if the struct is completely zeroed). If copy_struct_from_user() doesn't work with usize == 0, I would *much* prefer a patch which fixes that (effectively copy_struct_from_user() with a usize == 0 should just be a call to check_zeroed_user()). > + f = fdget(pidfd); > + if (!f.file) > + return -EBADF; > + > + pid = pidfd_pid(f.file); > + if (IS_ERR(pid)) { > + ret = PTR_ERR(pid); > + goto out; > + } > + > + ret = pidfd_getfd(pid, fd); > + > +out: > + fdput(f); > + return ret; > +} > -- > 2.20.1
On Fri, Dec 20, 2019 at 4:27 PM Aleksa Sarai <asarai@suse.de> wrote: > > On 2019-12-20, Sargun Dhillon <sargun@sargun.me> wrote: > > diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h > > new file mode 100644 > > index 000000000000..0a3fc922661d > > --- /dev/null > > +++ b/include/uapi/linux/pidfd.h > > @@ -0,0 +1,10 @@ > > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ > > +#ifndef _UAPI_LINUX_PIDFD_H > > +#define _UAPI_LINUX_PIDFD_H > > + > > +struct pidfd_getfd_options {}; > > Are empty structs well-defined in C (from memory, some compilers make > them non-zero in size)? Since we probably plan to add a flags field in > the future anyway, why not just have a __u64 flags which must be zeroed? > It's allowed in GCC: https://gcc.gnu.org/onlinedocs/gcc-8.1.0/gcc/Empty-Structures.html I can add an __aligned_u64 flags for now, and just say something like "reserved". This will also solve the latter issue, and I'll just use copy_struct_from_user, as long as Christian is okay with having an unused (reserved) flag member. > > + f = fdget(pidfd); > > + if (!f.file) > > + return -EBADF; > > + > > + pid = pidfd_pid(f.file); > > + if (IS_ERR(pid)) { > > + ret = PTR_ERR(pid); > > + goto out; > > + } > > + > > + ret = pidfd_getfd(pid, fd); > > + > > +out: > > + fdput(f); > > + return ret; > > +} > > -- > > 2.20.1 > > -- > Aleksa Sarai > Senior Software Engineer (Containers) > SUSE Linux GmbH > <https://www.cyphar.com/>
On Fri, Dec 20, 2019 at 11:28:13PM +0000, Sargun Dhillon wrote: > This syscall allows for the retrieval of file descriptors from other > processes, based on their pidfd. This is possible using ptrace, and > injection of parasitic code along with using SCM_RIGHTS to move > file descriptors between a tracee and a tracer. Unfortunately, ptrace > comes with a high cost of requiring the process to be stopped, and > breaks debuggers. This does not require stopping the process under > manipulation. > > One reason to use this is to allow sandboxers to take actions on file > descriptors on the behalf of another process. For example, this can be > combined with seccomp-bpf's user notification to do on-demand fd > extraction and take privileged actions. For example, it can be used > to bind a socket to a privileged port. > > /* prototype */ > /* > * pidfd_getfd_options is an extensible struct which can have options > * added to it. If options is NULL, size, and it will be ignored be > * ignored, otherwise, size should be set to sizeof(*options). If > * option is newer than the current kernel version, E2BIG will be > * returned. > */ > struct pidfd_getfd_options {}; > long pidfd_getfd(int pidfd, int fd, unsigned int flags, > struct pidfd_getfd_options *options, size_t size); The prototype advertises a flags argument but the actual +SYSCALL_DEFINE4(pidfd_getfd, int, pidfd, int, fd, + struct pidfd_getfd_options __user *, options, size_t, usize) does not have a flags argument... I think having a flags argument makes a lot of sense. I'm not sure what to think about the struct. I agree with Aleksa that having an empty struct is not a great idea. From a design perspective it seems very out of place. If we do a struct at all putting at least a single reserved field in there might makes more sense. In general, I think we need to have a _concrete_ reason why putting a struct versioned by size as arguments for this syscall. That means we need to have at least a concrete example for a new feature for this syscall where a flag would not convey enough information. And I'm not sure that there is a good one... I guess one thing I can think of is that a caller might want dup-like semantics, i.e. a caller might want to say: pidfd_getfd(<pidfd>, <fd-to-get>, <fd-number-to-want>, <flags>, ...) such that after pidfd_getfd() returns <fd-to-get> corresponds to <fd-number-to-want> in the caller. But that can also be achieved via: int fd = pidfd_getfd(<pidfd>, <fd-to-get>, <flags>, ...) int final_fd = dup3(fd, <newfd>, O_CLOEXEC) > > /* testing */ > Ran self-test suite on x86_64 +1 > > Signed-off-by: Sargun Dhillon <sargun@sargun.me> > --- > MAINTAINERS | 1 + > arch/alpha/kernel/syscalls/syscall.tbl | 1 + > arch/arm/tools/syscall.tbl | 1 + > arch/arm64/include/asm/unistd.h | 2 +- > arch/arm64/include/asm/unistd32.h | 2 + > arch/ia64/kernel/syscalls/syscall.tbl | 1 + > arch/m68k/kernel/syscalls/syscall.tbl | 1 + > arch/microblaze/kernel/syscalls/syscall.tbl | 1 + > arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + > arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + > arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + > arch/parisc/kernel/syscalls/syscall.tbl | 1 + > arch/powerpc/kernel/syscalls/syscall.tbl | 1 + > arch/s390/kernel/syscalls/syscall.tbl | 1 + > arch/sh/kernel/syscalls/syscall.tbl | 1 + > arch/sparc/kernel/syscalls/syscall.tbl | 1 + > arch/x86/entry/syscalls/syscall_32.tbl | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > arch/xtensa/kernel/syscalls/syscall.tbl | 1 + > include/linux/syscalls.h | 4 + > include/uapi/asm-generic/unistd.h | 3 +- > include/uapi/linux/pidfd.h | 10 ++ > kernel/pid.c | 115 ++++++++++++++++++++ > 23 files changed, 151 insertions(+), 2 deletions(-) > create mode 100644 include/uapi/linux/pidfd.h > > diff --git a/MAINTAINERS b/MAINTAINERS > index cc0a4a8ae06a..bc370ff59dbf 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -13014,6 +13014,7 @@ M: Christian Brauner <christian@brauner.io> > L: linux-kernel@vger.kernel.org > S: Maintained > T: git git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git > +F: include/uapi/linux/pidfd.h > F: samples/pidfd/ > F: tools/testing/selftests/pidfd/ > F: tools/testing/selftests/clone3/ > diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl > index 8e13b0b2928d..d1cac0d657b7 100644 > --- a/arch/alpha/kernel/syscalls/syscall.tbl > +++ b/arch/alpha/kernel/syscalls/syscall.tbl > @@ -475,3 +475,4 @@ > 543 common fspick sys_fspick > 544 common pidfd_open sys_pidfd_open > # 545 reserved for clone3 > +548 common pidfd_getfd sys_pidfd > diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl > index 6da7dc4d79cc..ba045e2f3a60 100644 > --- a/arch/arm/tools/syscall.tbl > +++ b/arch/arm/tools/syscall.tbl > @@ -449,3 +449,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h > index 2629a68b8724..b722e47377a5 100644 > --- a/arch/arm64/include/asm/unistd.h > +++ b/arch/arm64/include/asm/unistd.h > @@ -38,7 +38,7 @@ > #define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5) > #define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800) > > -#define __NR_compat_syscalls 436 > +#define __NR_compat_syscalls 439 > #endif > > #define __ARCH_WANT_SYS_CLONE > diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h > index 94ab29cf4f00..a8da97a2de41 100644 > --- a/arch/arm64/include/asm/unistd32.h > +++ b/arch/arm64/include/asm/unistd32.h > @@ -879,6 +879,8 @@ __SYSCALL(__NR_fspick, sys_fspick) > __SYSCALL(__NR_pidfd_open, sys_pidfd_open) > #define __NR_clone3 435 > __SYSCALL(__NR_clone3, sys_clone3) > +#define __NR_pidfd_getfd 438 > +__SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd) > > /* > * Please add new compat syscalls above this comment and update > diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl > index 36d5faf4c86c..2b11adfc860c 100644 > --- a/arch/ia64/kernel/syscalls/syscall.tbl > +++ b/arch/ia64/kernel/syscalls/syscall.tbl > @@ -356,3 +356,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > # 435 reserved for clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl > index a88a285a0e5f..44e879e98459 100644 > --- a/arch/m68k/kernel/syscalls/syscall.tbl > +++ b/arch/m68k/kernel/syscalls/syscall.tbl > @@ -435,3 +435,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > # 435 reserved for clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl > index 09b0cd7dab0a..7afa00125cc4 100644 > --- a/arch/microblaze/kernel/syscalls/syscall.tbl > +++ b/arch/microblaze/kernel/syscalls/syscall.tbl > @@ -441,3 +441,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl > index e7c5ab38e403..856d5ba34461 100644 > --- a/arch/mips/kernel/syscalls/syscall_n32.tbl > +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl > @@ -374,3 +374,4 @@ > 433 n32 fspick sys_fspick > 434 n32 pidfd_open sys_pidfd_open > 435 n32 clone3 __sys_clone3 > +438 n32 pidfd_getfd sys_pidfd_getfd > diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl > index 13cd66581f3b..2db6075352f3 100644 > --- a/arch/mips/kernel/syscalls/syscall_n64.tbl > +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl > @@ -350,3 +350,4 @@ > 433 n64 fspick sys_fspick > 434 n64 pidfd_open sys_pidfd_open > 435 n64 clone3 __sys_clone3 > +438 n64 pidfd_getfd sys_pidfd_getfd > diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl > index 353539ea4140..e9f9d4a9b105 100644 > --- a/arch/mips/kernel/syscalls/syscall_o32.tbl > +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl > @@ -423,3 +423,4 @@ > 433 o32 fspick sys_fspick > 434 o32 pidfd_open sys_pidfd_open > 435 o32 clone3 __sys_clone3 > +438 o32 pidfd_getfd sys_pidfd_getfd > diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl > index 285ff516150c..c58c7eb144ca 100644 > --- a/arch/parisc/kernel/syscalls/syscall.tbl > +++ b/arch/parisc/kernel/syscalls/syscall.tbl > @@ -433,3 +433,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3_wrapper > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl > index 43f736ed47f2..707609bfe3ea 100644 > --- a/arch/powerpc/kernel/syscalls/syscall.tbl > +++ b/arch/powerpc/kernel/syscalls/syscall.tbl > @@ -517,3 +517,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 nospu clone3 ppc_clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl > index 3054e9c035a3..185cd624face 100644 > --- a/arch/s390/kernel/syscalls/syscall.tbl > +++ b/arch/s390/kernel/syscalls/syscall.tbl > @@ -438,3 +438,4 @@ > 433 common fspick sys_fspick sys_fspick > 434 common pidfd_open sys_pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3 sys_clone3 > +438 common pidfd_getfd sys_pidfd_getfd sys_pidfd_getfd > diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl > index b5ed26c4c005..88f90895aad8 100644 > --- a/arch/sh/kernel/syscalls/syscall.tbl > +++ b/arch/sh/kernel/syscalls/syscall.tbl > @@ -438,3 +438,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > # 435 reserved for clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl > index 8c8cc7537fb2..218df6a2326e 100644 > --- a/arch/sparc/kernel/syscalls/syscall.tbl > +++ b/arch/sparc/kernel/syscalls/syscall.tbl > @@ -481,3 +481,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > # 435 reserved for clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl > index 15908eb9b17e..9c3101b65e0f 100644 > --- a/arch/x86/entry/syscalls/syscall_32.tbl > +++ b/arch/x86/entry/syscalls/syscall_32.tbl > @@ -440,3 +440,4 @@ > 433 i386 fspick sys_fspick __ia32_sys_fspick > 434 i386 pidfd_open sys_pidfd_open __ia32_sys_pidfd_open > 435 i386 clone3 sys_clone3 __ia32_sys_clone3 > +438 i386 pidfd_getfd sys_pidfd_getfd __ia32_sys_pidfd_getfd > diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl > index c29976eca4a8..cef85db75a62 100644 > --- a/arch/x86/entry/syscalls/syscall_64.tbl > +++ b/arch/x86/entry/syscalls/syscall_64.tbl > @@ -357,6 +357,7 @@ > 433 common fspick __x64_sys_fspick > 434 common pidfd_open __x64_sys_pidfd_open > 435 common clone3 __x64_sys_clone3/ptregs > +438 common pidfd_getfd __x64_sys_pidfd_getfd > > # > # x32-specific system call numbers start at 512 to avoid cache impact > diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl > index 25f4de729a6d..ae15183def12 100644 > --- a/arch/xtensa/kernel/syscalls/syscall.tbl > +++ b/arch/xtensa/kernel/syscalls/syscall.tbl > @@ -406,3 +406,4 @@ > 433 common fspick sys_fspick > 434 common pidfd_open sys_pidfd_open > 435 common clone3 sys_clone3 > +438 common pidfd_getfd sys_pidfd_getfd > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h > index 2960dedcfde8..62fe706329d1 100644 > --- a/include/linux/syscalls.h > +++ b/include/linux/syscalls.h > @@ -69,6 +69,7 @@ struct rseq; > union bpf_attr; > struct io_uring_params; > struct clone_args; > +struct pidfd_getfd_options; > > #include <linux/types.h> > #include <linux/aio_abi.h> > @@ -1000,6 +1001,9 @@ asmlinkage long sys_fspick(int dfd, const char __user *path, unsigned int flags) > asmlinkage long sys_pidfd_send_signal(int pidfd, int sig, > siginfo_t __user *info, > unsigned int flags); > +asmlinkage long sys_pidfd_getfd(int pidfd, int fd, > + struct pidfd_getfd_options __user *options, > + size_t, usize); > > /* > * Architecture-specific system calls > diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h > index 1fc8faa6e973..f358488366f6 100644 > --- a/include/uapi/asm-generic/unistd.h > +++ b/include/uapi/asm-generic/unistd.h > @@ -850,9 +850,10 @@ __SYSCALL(__NR_pidfd_open, sys_pidfd_open) > #define __NR_clone3 435 > __SYSCALL(__NR_clone3, sys_clone3) > #endif > +#define __NR_pidfd_getfd 438 > > #undef __NR_syscalls > -#define __NR_syscalls 436 > +#define __NR_syscalls 439 > > /* > * 32 bit systems traditionally used different > diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h > new file mode 100644 > index 000000000000..0a3fc922661d > --- /dev/null > +++ b/include/uapi/linux/pidfd.h > @@ -0,0 +1,10 @@ > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ > +#ifndef _UAPI_LINUX_PIDFD_H > +#define _UAPI_LINUX_PIDFD_H > + > +struct pidfd_getfd_options {}; > + > +#define PIDFD_GETFD_OPTIONS_SIZE_VER0 0 > +#define PIDFD_GETFD_OPTIONS_SIZE_LATEST PIDFD_GETFD_OPTIONS_SIZE_VER0 > + > +#endif /* _UAPI_LINUX_PIDFD_H */ > diff --git a/kernel/pid.c b/kernel/pid.c > index 2278e249141d..2a9cb4be383f 100644 > --- a/kernel/pid.c > +++ b/kernel/pid.c > @@ -42,6 +42,7 @@ > #include <linux/sched/signal.h> > #include <linux/sched/task.h> > #include <linux/idr.h> > +#include <uapi/linux/pidfd.h> > > struct pid init_struct_pid = { > .count = REFCOUNT_INIT(1), > @@ -578,3 +579,117 @@ void __init pid_idr_init(void) > init_pid_ns.pid_cachep = KMEM_CACHE(pid, > SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT); > } > + > +static struct file *__pidfd_getfd_fget_task(struct task_struct *task, u32 fd) > +{ > + struct file *file; > + int ret; > + > + ret = mutex_lock_killable(&task->signal->cred_guard_mutex); > + if (ret) > + return ERR_PTR(ret); > + > + if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS)) { > + file = ERR_PTR(-EPERM); > + goto out; > + } > + > + file = fget_task(task, fd); > + if (!file) > + file = ERR_PTR(-EBADF); > + > +out: > + mutex_unlock(&task->signal->cred_guard_mutex); > + return file; > +} > + > +static long pidfd_getfd(struct pid *pid, u32 fd) > +{ > + struct task_struct *task; > + struct file *file; > + int ret, retfd; > + > + task = get_pid_task(pid, PIDTYPE_PID); > + if (!task) > + return -ESRCH; > + > + file = __pidfd_getfd_fget_task(task, fd); > + put_task_struct(task); > + if (IS_ERR(file)) > + return PTR_ERR(file); > + > + retfd = get_unused_fd_flags(O_CLOEXEC); > + if (retfd < 0) { > + ret = retfd; > + goto out; > + } > + > + /* > + * security_file_receive must come last since it may have side effects > + * and cannot be reversed. > + */ > + ret = security_file_receive(file); > + if (ret) > + goto out_put_fd; > + > + fd_install(retfd, file); > + return retfd; > + > +out_put_fd: > + put_unused_fd(retfd); > +out: > + fput(file); > + return ret; > +} > + > +/** > + * sys_pidfd_getfd() - Get a file descriptor from another process > + * > + * @pidfd: file descriptor of the process > + * @fd: the file descriptor number to get > + * @options: options on how to get the fd > + * @usize: the size of options > + * > + * This syscall requires that the process has the ability to ptrace the > + * process represented by the pidfd. It will return a duplicated version > + * of the file descriptor on success. The process who which is having s/who which/which/ > + * its file descriptor taken is otherwise unaffected. If options is NULL > + * it is ignored along with usize. > + * > + * Return: On success, a file descriptor with cloexec is returned. > + * On error, a negative errno number will be returned. > + */ > +SYSCALL_DEFINE4(pidfd_getfd, int, pidfd, int, fd, > + struct pidfd_getfd_options __user *, options, size_t, usize) > +{ > + struct pid *pid; > + struct fd f; > + int ret; > + > + BUILD_BUG_ON(sizeof(struct pidfd_getfd_options) != PIDFD_GETFD_OPTIONS_SIZE_LATEST); > + > + /* > + * options is currently unused, verify it's unset or if it is set, > + * ensure that size is 0. > + * > + * In the future, this will need to adopt copy_struct_from_user. > + */ > + if (options && usize > PIDFD_GETFD_OPTIONS_SIZE_VER0) > + return -E2BIG; > + > + f = fdget(pidfd); > + if (!f.file) > + return -EBADF; > + > + pid = pidfd_pid(f.file); > + if (IS_ERR(pid)) { > + ret = PTR_ERR(pid); > + goto out; > + } > + > + ret = pidfd_getfd(pid, fd); > + > +out: > + fdput(f); > + return ret; > +} > -- > 2.20.1 >
, On Sun, Dec 22, 2019 at 4:48 AM Christian Brauner <christian.brauner@ubuntu.com> wrote: > > On Fri, Dec 20, 2019 at 11:28:13PM +0000, Sargun Dhillon wrote: > > This syscall allows for the retrieval of file descriptors from other > > processes, based on their pidfd. This is possible using ptrace, and > > injection of parasitic code along with using SCM_RIGHTS to move > > file descriptors between a tracee and a tracer. Unfortunately, ptrace > > comes with a high cost of requiring the process to be stopped, and > > breaks debuggers. This does not require stopping the process under > > manipulation. > > > > One reason to use this is to allow sandboxers to take actions on file > > descriptors on the behalf of another process. For example, this can be > > combined with seccomp-bpf's user notification to do on-demand fd > > extraction and take privileged actions. For example, it can be used > > to bind a socket to a privileged port. > > > > /* prototype */ > > /* > > * pidfd_getfd_options is an extensible struct which can have options > > * added to it. If options is NULL, size, and it will be ignored be > > * ignored, otherwise, size should be set to sizeof(*options). If > > * option is newer than the current kernel version, E2BIG will be > > * returned. > > */ > > struct pidfd_getfd_options {}; > > long pidfd_getfd(int pidfd, int fd, unsigned int flags, > > struct pidfd_getfd_options *options, size_t size); That's embarrassing. This was supposed to read: long pidfd_getfd(int pidfd, int fd, struct pidfd_get_options *options, size_t size); > > The prototype advertises a flags argument but the actual > > +SYSCALL_DEFINE4(pidfd_getfd, int, pidfd, int, fd, > + struct pidfd_getfd_options __user *, options, size_t, usize) > > does not have a flags argument... > > I think having a flags argument makes a lot of sense. > > I'm not sure what to think about the struct. I agree with Aleksa that > having an empty struct is not a great idea. From a design perspective it > seems very out of place. If we do a struct at all putting at least a > single reserved field in there might makes more sense. > > In general, I think we need to have a _concrete_ reason why putting a > struct versioned by size as arguments for this syscall. > That means we need to have at least a concrete example for a new feature > for this syscall where a flag would not convey enough information. I can think of at least two reasons we need flags: * Clearing cgroup flags * Closing the process under manipulation's FD when we fetch it. The original reason for wanting to have two places where we can put flags was to have a different field for fd flags vs. call flags. I'm not sure there's any flags you'd want to set. Given this, if we want to go down the route of a syscall, we should just leave it as a __u64 flags, and drop the pointer to the struct, if we're not worried about that. > > And I'm not sure that there is a good one... I guess one thing I can > think of is that a caller might want dup-like semantics, i.e. a caller > might want to say: > > pidfd_getfd(<pidfd>, <fd-to-get>, <fd-number-to-want>, <flags>, ...) > > such that after pidfd_getfd() returns <fd-to-get> corresponds to > <fd-number-to-want> in the caller. But that can also be achieved via: > int fd = pidfd_getfd(<pidfd>, <fd-to-get>, <flags>, ...) > int final_fd = dup3(fd, <newfd>, O_CLOEXEC) > > > > > /* testing */ > > Ran self-test suite on x86_64 > > +1 >
On Sun, Dec 22, 2019 at 10:36:42AM -0800, Sargun Dhillon wrote: > , On Sun, Dec 22, 2019 at 4:48 AM Christian Brauner > <christian.brauner@ubuntu.com> wrote: > > > > On Fri, Dec 20, 2019 at 11:28:13PM +0000, Sargun Dhillon wrote: > > > This syscall allows for the retrieval of file descriptors from other > > > processes, based on their pidfd. This is possible using ptrace, and > > > injection of parasitic code along with using SCM_RIGHTS to move > > > file descriptors between a tracee and a tracer. Unfortunately, ptrace > > > comes with a high cost of requiring the process to be stopped, and > > > breaks debuggers. This does not require stopping the process under > > > manipulation. > > > > > > One reason to use this is to allow sandboxers to take actions on file > > > descriptors on the behalf of another process. For example, this can be > > > combined with seccomp-bpf's user notification to do on-demand fd > > > extraction and take privileged actions. For example, it can be used > > > to bind a socket to a privileged port. > > > > > > /* prototype */ > > > /* > > > * pidfd_getfd_options is an extensible struct which can have options > > > * added to it. If options is NULL, size, and it will be ignored be > > > * ignored, otherwise, size should be set to sizeof(*options). If > > > * option is newer than the current kernel version, E2BIG will be > > > * returned. > > > */ > > > struct pidfd_getfd_options {}; > > > long pidfd_getfd(int pidfd, int fd, unsigned int flags, > > > struct pidfd_getfd_options *options, size_t size); > That's embarrassing. This was supposed to read: > long pidfd_getfd(int pidfd, int fd, struct pidfd_get_options *options, > size_t size); > > > > > The prototype advertises a flags argument but the actual > > > > +SYSCALL_DEFINE4(pidfd_getfd, int, pidfd, int, fd, > > + struct pidfd_getfd_options __user *, options, size_t, usize) > > > > does not have a flags argument... > > > > I think having a flags argument makes a lot of sense. > > > > I'm not sure what to think about the struct. I agree with Aleksa that > > having an empty struct is not a great idea. From a design perspective it > > seems very out of place. If we do a struct at all putting at least a > > single reserved field in there might makes more sense. > > > > In general, I think we need to have a _concrete_ reason why putting a > > struct versioned by size as arguments for this syscall. > > That means we need to have at least a concrete example for a new feature > > for this syscall where a flag would not convey enough information. > I can think of at least two reasons we need flags: > * Clearing cgroup flags > * Closing the process under manipulation's FD when we fetch it. > > The original reason for wanting to have two places where we can put > flags was to have a different field for fd flags vs. call flags. I'm not sure > there's any flags you'd want to set. > > Given this, if we want to go down the route of a syscall, we should just > leave it as a __u64 flags, and drop the pointer to the struct, if we're I think it needs to be an unsigned int. Having a 64bit register arg is really messy on 32bit and means you need to have a compat syscall implementation which handles this. Christian
Hi Sargun,
Thank you for the patch! Yet something to improve:
[auto build test ERROR on kselftest/next]
[also build test ERROR on arm64/for-next/core linus/master v5.5-rc3]
[cannot apply to tip/x86/asm next-20191220]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
url: https://github.com/0day-ci/linux/commits/Sargun-Dhillon/Add-pidfd_getfd-syscall/20191224-061915
base: https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git next
config: i386-randconfig-a001-20191224 (attached as .config)
compiler: gcc-4.9 (Debian 4.9.2-10+deb8u1) 4.9.2
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>
All errors (new ones prefixed by >>):
In file included from drivers//ptp/ptp_clock.c:16:0:
>> include/linux/syscalls.h:1006:13: error: unknown type name 'usize'
size_t, usize);
^
vim +/usize +1006 include/linux/syscalls.h
864
865 /* mm/, CONFIG_MMU only */
866 asmlinkage long sys_swapon(const char __user *specialfile, int swap_flags);
867 asmlinkage long sys_swapoff(const char __user *specialfile);
868 asmlinkage long sys_mprotect(unsigned long start, size_t len,
869 unsigned long prot);
870 asmlinkage long sys_msync(unsigned long start, size_t len, int flags);
871 asmlinkage long sys_mlock(unsigned long start, size_t len);
872 asmlinkage long sys_munlock(unsigned long start, size_t len);
873 asmlinkage long sys_mlockall(int flags);
874 asmlinkage long sys_munlockall(void);
875 asmlinkage long sys_mincore(unsigned long start, size_t len,
876 unsigned char __user * vec);
877 asmlinkage long sys_madvise(unsigned long start, size_t len, int behavior);
878 asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
879 unsigned long prot, unsigned long pgoff,
880 unsigned long flags);
881 asmlinkage long sys_mbind(unsigned long start, unsigned long len,
882 unsigned long mode,
883 const unsigned long __user *nmask,
884 unsigned long maxnode,
885 unsigned flags);
886 asmlinkage long sys_get_mempolicy(int __user *policy,
887 unsigned long __user *nmask,
888 unsigned long maxnode,
889 unsigned long addr, unsigned long flags);
890 asmlinkage long sys_set_mempolicy(int mode, const unsigned long __user *nmask,
891 unsigned long maxnode);
892 asmlinkage long sys_migrate_pages(pid_t pid, unsigned long maxnode,
893 const unsigned long __user *from,
894 const unsigned long __user *to);
895 asmlinkage long sys_move_pages(pid_t pid, unsigned long nr_pages,
896 const void __user * __user *pages,
897 const int __user *nodes,
898 int __user *status,
899 int flags);
900
901 asmlinkage long sys_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig,
902 siginfo_t __user *uinfo);
903 asmlinkage long sys_perf_event_open(
904 struct perf_event_attr __user *attr_uptr,
905 pid_t pid, int cpu, int group_fd, unsigned long flags);
906 asmlinkage long sys_accept4(int, struct sockaddr __user *, int __user *, int);
907 asmlinkage long sys_recvmmsg(int fd, struct mmsghdr __user *msg,
908 unsigned int vlen, unsigned flags,
909 struct __kernel_timespec __user *timeout);
910 asmlinkage long sys_recvmmsg_time32(int fd, struct mmsghdr __user *msg,
911 unsigned int vlen, unsigned flags,
912 struct old_timespec32 __user *timeout);
913
914 asmlinkage long sys_wait4(pid_t pid, int __user *stat_addr,
915 int options, struct rusage __user *ru);
916 asmlinkage long sys_prlimit64(pid_t pid, unsigned int resource,
917 const struct rlimit64 __user *new_rlim,
918 struct rlimit64 __user *old_rlim);
919 asmlinkage long sys_fanotify_init(unsigned int flags, unsigned int event_f_flags);
920 asmlinkage long sys_fanotify_mark(int fanotify_fd, unsigned int flags,
921 u64 mask, int fd,
922 const char __user *pathname);
923 asmlinkage long sys_name_to_handle_at(int dfd, const char __user *name,
924 struct file_handle __user *handle,
925 int __user *mnt_id, int flag);
926 asmlinkage long sys_open_by_handle_at(int mountdirfd,
927 struct file_handle __user *handle,
928 int flags);
929 asmlinkage long sys_clock_adjtime(clockid_t which_clock,
930 struct __kernel_timex __user *tx);
931 asmlinkage long sys_clock_adjtime32(clockid_t which_clock,
932 struct old_timex32 __user *tx);
933 asmlinkage long sys_syncfs(int fd);
934 asmlinkage long sys_setns(int fd, int nstype);
935 asmlinkage long sys_pidfd_open(pid_t pid, unsigned int flags);
936 asmlinkage long sys_sendmmsg(int fd, struct mmsghdr __user *msg,
937 unsigned int vlen, unsigned flags);
938 asmlinkage long sys_process_vm_readv(pid_t pid,
939 const struct iovec __user *lvec,
940 unsigned long liovcnt,
941 const struct iovec __user *rvec,
942 unsigned long riovcnt,
943 unsigned long flags);
944 asmlinkage long sys_process_vm_writev(pid_t pid,
945 const struct iovec __user *lvec,
946 unsigned long liovcnt,
947 const struct iovec __user *rvec,
948 unsigned long riovcnt,
949 unsigned long flags);
950 asmlinkage long sys_kcmp(pid_t pid1, pid_t pid2, int type,
951 unsigned long idx1, unsigned long idx2);
952 asmlinkage long sys_finit_module(int fd, const char __user *uargs, int flags);
953 asmlinkage long sys_sched_setattr(pid_t pid,
954 struct sched_attr __user *attr,
955 unsigned int flags);
956 asmlinkage long sys_sched_getattr(pid_t pid,
957 struct sched_attr __user *attr,
958 unsigned int size,
959 unsigned int flags);
960 asmlinkage long sys_renameat2(int olddfd, const char __user *oldname,
961 int newdfd, const char __user *newname,
962 unsigned int flags);
963 asmlinkage long sys_seccomp(unsigned int op, unsigned int flags,
964 void __user *uargs);
965 asmlinkage long sys_getrandom(char __user *buf, size_t count,
966 unsigned int flags);
967 asmlinkage long sys_memfd_create(const char __user *uname_ptr, unsigned int flags);
968 asmlinkage long sys_bpf(int cmd, union bpf_attr *attr, unsigned int size);
969 asmlinkage long sys_execveat(int dfd, const char __user *filename,
970 const char __user *const __user *argv,
971 const char __user *const __user *envp, int flags);
972 asmlinkage long sys_userfaultfd(int flags);
973 asmlinkage long sys_membarrier(int cmd, int flags);
974 asmlinkage long sys_mlock2(unsigned long start, size_t len, int flags);
975 asmlinkage long sys_copy_file_range(int fd_in, loff_t __user *off_in,
976 int fd_out, loff_t __user *off_out,
977 size_t len, unsigned int flags);
978 asmlinkage long sys_preadv2(unsigned long fd, const struct iovec __user *vec,
979 unsigned long vlen, unsigned long pos_l, unsigned long pos_h,
980 rwf_t flags);
981 asmlinkage long sys_pwritev2(unsigned long fd, const struct iovec __user *vec,
982 unsigned long vlen, unsigned long pos_l, unsigned long pos_h,
983 rwf_t flags);
984 asmlinkage long sys_pkey_mprotect(unsigned long start, size_t len,
985 unsigned long prot, int pkey);
986 asmlinkage long sys_pkey_alloc(unsigned long flags, unsigned long init_val);
987 asmlinkage long sys_pkey_free(int pkey);
988 asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags,
989 unsigned mask, struct statx __user *buffer);
990 asmlinkage long sys_rseq(struct rseq __user *rseq, uint32_t rseq_len,
991 int flags, uint32_t sig);
992 asmlinkage long sys_open_tree(int dfd, const char __user *path, unsigned flags);
993 asmlinkage long sys_move_mount(int from_dfd, const char __user *from_path,
994 int to_dfd, const char __user *to_path,
995 unsigned int ms_flags);
996 asmlinkage long sys_fsopen(const char __user *fs_name, unsigned int flags);
997 asmlinkage long sys_fsconfig(int fs_fd, unsigned int cmd, const char __user *key,
998 const void __user *value, int aux);
999 asmlinkage long sys_fsmount(int fs_fd, unsigned int flags, unsigned int ms_flags);
1000 asmlinkage long sys_fspick(int dfd, const char __user *path, unsigned int flags);
1001 asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
1002 siginfo_t __user *info,
1003 unsigned int flags);
1004 asmlinkage long sys_pidfd_getfd(int pidfd, int fd,
1005 struct pidfd_getfd_options __user *options,
> 1006 size_t, usize);
1007
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel Corporation
diff --git a/MAINTAINERS b/MAINTAINERS index cc0a4a8ae06a..bc370ff59dbf 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -13014,6 +13014,7 @@ M: Christian Brauner <christian@brauner.io> L: linux-kernel@vger.kernel.org S: Maintained T: git git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux.git +F: include/uapi/linux/pidfd.h F: samples/pidfd/ F: tools/testing/selftests/pidfd/ F: tools/testing/selftests/clone3/ diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl index 8e13b0b2928d..d1cac0d657b7 100644 --- a/arch/alpha/kernel/syscalls/syscall.tbl +++ b/arch/alpha/kernel/syscalls/syscall.tbl @@ -475,3 +475,4 @@ 543 common fspick sys_fspick 544 common pidfd_open sys_pidfd_open # 545 reserved for clone3 +548 common pidfd_getfd sys_pidfd diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl index 6da7dc4d79cc..ba045e2f3a60 100644 --- a/arch/arm/tools/syscall.tbl +++ b/arch/arm/tools/syscall.tbl @@ -449,3 +449,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h index 2629a68b8724..b722e47377a5 100644 --- a/arch/arm64/include/asm/unistd.h +++ b/arch/arm64/include/asm/unistd.h @@ -38,7 +38,7 @@ #define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5) #define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800) -#define __NR_compat_syscalls 436 +#define __NR_compat_syscalls 439 #endif #define __ARCH_WANT_SYS_CLONE diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h index 94ab29cf4f00..a8da97a2de41 100644 --- a/arch/arm64/include/asm/unistd32.h +++ b/arch/arm64/include/asm/unistd32.h @@ -879,6 +879,8 @@ __SYSCALL(__NR_fspick, sys_fspick) __SYSCALL(__NR_pidfd_open, sys_pidfd_open) #define __NR_clone3 435 __SYSCALL(__NR_clone3, sys_clone3) +#define __NR_pidfd_getfd 438 +__SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd) /* * Please add new compat syscalls above this comment and update diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl index 36d5faf4c86c..2b11adfc860c 100644 --- a/arch/ia64/kernel/syscalls/syscall.tbl +++ b/arch/ia64/kernel/syscalls/syscall.tbl @@ -356,3 +356,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl index a88a285a0e5f..44e879e98459 100644 --- a/arch/m68k/kernel/syscalls/syscall.tbl +++ b/arch/m68k/kernel/syscalls/syscall.tbl @@ -435,3 +435,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl index 09b0cd7dab0a..7afa00125cc4 100644 --- a/arch/microblaze/kernel/syscalls/syscall.tbl +++ b/arch/microblaze/kernel/syscalls/syscall.tbl @@ -441,3 +441,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl index e7c5ab38e403..856d5ba34461 100644 --- a/arch/mips/kernel/syscalls/syscall_n32.tbl +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl @@ -374,3 +374,4 @@ 433 n32 fspick sys_fspick 434 n32 pidfd_open sys_pidfd_open 435 n32 clone3 __sys_clone3 +438 n32 pidfd_getfd sys_pidfd_getfd diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl index 13cd66581f3b..2db6075352f3 100644 --- a/arch/mips/kernel/syscalls/syscall_n64.tbl +++ b/arch/mips/kernel/syscalls/syscall_n64.tbl @@ -350,3 +350,4 @@ 433 n64 fspick sys_fspick 434 n64 pidfd_open sys_pidfd_open 435 n64 clone3 __sys_clone3 +438 n64 pidfd_getfd sys_pidfd_getfd diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl index 353539ea4140..e9f9d4a9b105 100644 --- a/arch/mips/kernel/syscalls/syscall_o32.tbl +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl @@ -423,3 +423,4 @@ 433 o32 fspick sys_fspick 434 o32 pidfd_open sys_pidfd_open 435 o32 clone3 __sys_clone3 +438 o32 pidfd_getfd sys_pidfd_getfd diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl index 285ff516150c..c58c7eb144ca 100644 --- a/arch/parisc/kernel/syscalls/syscall.tbl +++ b/arch/parisc/kernel/syscalls/syscall.tbl @@ -433,3 +433,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3_wrapper +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl index 43f736ed47f2..707609bfe3ea 100644 --- a/arch/powerpc/kernel/syscalls/syscall.tbl +++ b/arch/powerpc/kernel/syscalls/syscall.tbl @@ -517,3 +517,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 nospu clone3 ppc_clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl index 3054e9c035a3..185cd624face 100644 --- a/arch/s390/kernel/syscalls/syscall.tbl +++ b/arch/s390/kernel/syscalls/syscall.tbl @@ -438,3 +438,4 @@ 433 common fspick sys_fspick sys_fspick 434 common pidfd_open sys_pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 sys_clone3 +438 common pidfd_getfd sys_pidfd_getfd sys_pidfd_getfd diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl index b5ed26c4c005..88f90895aad8 100644 --- a/arch/sh/kernel/syscalls/syscall.tbl +++ b/arch/sh/kernel/syscalls/syscall.tbl @@ -438,3 +438,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl index 8c8cc7537fb2..218df6a2326e 100644 --- a/arch/sparc/kernel/syscalls/syscall.tbl +++ b/arch/sparc/kernel/syscalls/syscall.tbl @@ -481,3 +481,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open # 435 reserved for clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index 15908eb9b17e..9c3101b65e0f 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -440,3 +440,4 @@ 433 i386 fspick sys_fspick __ia32_sys_fspick 434 i386 pidfd_open sys_pidfd_open __ia32_sys_pidfd_open 435 i386 clone3 sys_clone3 __ia32_sys_clone3 +438 i386 pidfd_getfd sys_pidfd_getfd __ia32_sys_pidfd_getfd diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index c29976eca4a8..cef85db75a62 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -357,6 +357,7 @@ 433 common fspick __x64_sys_fspick 434 common pidfd_open __x64_sys_pidfd_open 435 common clone3 __x64_sys_clone3/ptregs +438 common pidfd_getfd __x64_sys_pidfd_getfd # # x32-specific system call numbers start at 512 to avoid cache impact diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl index 25f4de729a6d..ae15183def12 100644 --- a/arch/xtensa/kernel/syscalls/syscall.tbl +++ b/arch/xtensa/kernel/syscalls/syscall.tbl @@ -406,3 +406,4 @@ 433 common fspick sys_fspick 434 common pidfd_open sys_pidfd_open 435 common clone3 sys_clone3 +438 common pidfd_getfd sys_pidfd_getfd diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 2960dedcfde8..62fe706329d1 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -69,6 +69,7 @@ struct rseq; union bpf_attr; struct io_uring_params; struct clone_args; +struct pidfd_getfd_options; #include <linux/types.h> #include <linux/aio_abi.h> @@ -1000,6 +1001,9 @@ asmlinkage long sys_fspick(int dfd, const char __user *path, unsigned int flags) asmlinkage long sys_pidfd_send_signal(int pidfd, int sig, siginfo_t __user *info, unsigned int flags); +asmlinkage long sys_pidfd_getfd(int pidfd, int fd, + struct pidfd_getfd_options __user *options, + size_t, usize); /* * Architecture-specific system calls diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index 1fc8faa6e973..f358488366f6 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -850,9 +850,10 @@ __SYSCALL(__NR_pidfd_open, sys_pidfd_open) #define __NR_clone3 435 __SYSCALL(__NR_clone3, sys_clone3) #endif +#define __NR_pidfd_getfd 438 #undef __NR_syscalls -#define __NR_syscalls 436 +#define __NR_syscalls 439 /* * 32 bit systems traditionally used different diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h new file mode 100644 index 000000000000..0a3fc922661d --- /dev/null +++ b/include/uapi/linux/pidfd.h @@ -0,0 +1,10 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _UAPI_LINUX_PIDFD_H +#define _UAPI_LINUX_PIDFD_H + +struct pidfd_getfd_options {}; + +#define PIDFD_GETFD_OPTIONS_SIZE_VER0 0 +#define PIDFD_GETFD_OPTIONS_SIZE_LATEST PIDFD_GETFD_OPTIONS_SIZE_VER0 + +#endif /* _UAPI_LINUX_PIDFD_H */ diff --git a/kernel/pid.c b/kernel/pid.c index 2278e249141d..2a9cb4be383f 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -42,6 +42,7 @@ #include <linux/sched/signal.h> #include <linux/sched/task.h> #include <linux/idr.h> +#include <uapi/linux/pidfd.h> struct pid init_struct_pid = { .count = REFCOUNT_INIT(1), @@ -578,3 +579,117 @@ void __init pid_idr_init(void) init_pid_ns.pid_cachep = KMEM_CACHE(pid, SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT); } + +static struct file *__pidfd_getfd_fget_task(struct task_struct *task, u32 fd) +{ + struct file *file; + int ret; + + ret = mutex_lock_killable(&task->signal->cred_guard_mutex); + if (ret) + return ERR_PTR(ret); + + if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_REALCREDS)) { + file = ERR_PTR(-EPERM); + goto out; + } + + file = fget_task(task, fd); + if (!file) + file = ERR_PTR(-EBADF); + +out: + mutex_unlock(&task->signal->cred_guard_mutex); + return file; +} + +static long pidfd_getfd(struct pid *pid, u32 fd) +{ + struct task_struct *task; + struct file *file; + int ret, retfd; + + task = get_pid_task(pid, PIDTYPE_PID); + if (!task) + return -ESRCH; + + file = __pidfd_getfd_fget_task(task, fd); + put_task_struct(task); + if (IS_ERR(file)) + return PTR_ERR(file); + + retfd = get_unused_fd_flags(O_CLOEXEC); + if (retfd < 0) { + ret = retfd; + goto out; + } + + /* + * security_file_receive must come last since it may have side effects + * and cannot be reversed. + */ + ret = security_file_receive(file); + if (ret) + goto out_put_fd; + + fd_install(retfd, file); + return retfd; + +out_put_fd: + put_unused_fd(retfd); +out: + fput(file); + return ret; +} + +/** + * sys_pidfd_getfd() - Get a file descriptor from another process + * + * @pidfd: file descriptor of the process + * @fd: the file descriptor number to get + * @options: options on how to get the fd + * @usize: the size of options + * + * This syscall requires that the process has the ability to ptrace the + * process represented by the pidfd. It will return a duplicated version + * of the file descriptor on success. The process who which is having + * its file descriptor taken is otherwise unaffected. If options is NULL + * it is ignored along with usize. + * + * Return: On success, a file descriptor with cloexec is returned. + * On error, a negative errno number will be returned. + */ +SYSCALL_DEFINE4(pidfd_getfd, int, pidfd, int, fd, + struct pidfd_getfd_options __user *, options, size_t, usize) +{ + struct pid *pid; + struct fd f; + int ret; + + BUILD_BUG_ON(sizeof(struct pidfd_getfd_options) != PIDFD_GETFD_OPTIONS_SIZE_LATEST); + + /* + * options is currently unused, verify it's unset or if it is set, + * ensure that size is 0. + * + * In the future, this will need to adopt copy_struct_from_user. + */ + if (options && usize > PIDFD_GETFD_OPTIONS_SIZE_VER0) + return -E2BIG; + + f = fdget(pidfd); + if (!f.file) + return -EBADF; + + pid = pidfd_pid(f.file); + if (IS_ERR(pid)) { + ret = PTR_ERR(pid); + goto out; + } + + ret = pidfd_getfd(pid, fd); + +out: + fdput(f); + return ret; +}
This syscall allows for the retrieval of file descriptors from other processes, based on their pidfd. This is possible using ptrace, and injection of parasitic code along with using SCM_RIGHTS to move file descriptors between a tracee and a tracer. Unfortunately, ptrace comes with a high cost of requiring the process to be stopped, and breaks debuggers. This does not require stopping the process under manipulation. One reason to use this is to allow sandboxers to take actions on file descriptors on the behalf of another process. For example, this can be combined with seccomp-bpf's user notification to do on-demand fd extraction and take privileged actions. For example, it can be used to bind a socket to a privileged port. /* prototype */ /* * pidfd_getfd_options is an extensible struct which can have options * added to it. If options is NULL, size, and it will be ignored be * ignored, otherwise, size should be set to sizeof(*options). If * option is newer than the current kernel version, E2BIG will be * returned. */ struct pidfd_getfd_options {}; long pidfd_getfd(int pidfd, int fd, unsigned int flags, struct pidfd_getfd_options *options, size_t size); /* testing */ Ran self-test suite on x86_64 Signed-off-by: Sargun Dhillon <sargun@sargun.me> --- MAINTAINERS | 1 + arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 2 + arch/ia64/kernel/syscalls/syscall.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/mips/kernel/syscalls/syscall_n64.tbl | 1 + arch/mips/kernel/syscalls/syscall_o32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + include/linux/syscalls.h | 4 + include/uapi/asm-generic/unistd.h | 3 +- include/uapi/linux/pidfd.h | 10 ++ kernel/pid.c | 115 ++++++++++++++++++++ 23 files changed, 151 insertions(+), 2 deletions(-) create mode 100644 include/uapi/linux/pidfd.h