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[92.34.215.243]) by smtp.gmail.com with ESMTPSA id x128sm9837994lff.67.2020.03.31.06.37.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Mar 2020 06:37:45 -0700 (PDT) From: Linus Walleij To: Theodore Ts'o , Andreas Dilger Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, qemu-devel@nongnu.org, Linus Walleij , Florian Weimer , Peter Maydell , Andy Lutomirski Subject: [PATCH] fcntl: Add 32bit filesystem mode Date: Tue, 31 Mar 2020 15:35:36 +0200 Message-Id: <20200331133536.3328-1-linus.walleij@linaro.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org It was brought to my attention that this bug from 2018 was still unresolved: 32 bit emulators like QEMU were given 64 bit hashes when running 32 bit emulation on 64 bit systems. This adds a fcntl() operation to set the underlying filesystem into 32bit mode even if the file hanle was opened using 64bit mode without the compat syscalls. Programs that need the 32 bit file system behavior need to issue a fcntl() system call such as in this example: #define F_SET_FILE_32BIT_FS (1024 + 15) int main(int argc, char** argv) { DIR* dir; int err; int fd; dir = opendir("/boot"); fd = dirfd(dir); err = fcntl(fd, F_SET_FILE_32BIT_FS); if (err) { printf("fcntl() failed! err=%d\n", err); return 1; } printf("dir=%p\n", dir); printf("readdir(dir)=%p\n", readdir(dir)); printf("errno=%d: %s\n", errno, strerror(errno)); return 0; } This can be pretty hard to test since C libraries and linux userspace security extensions aggressively filter the parameters that are passed down and allowed to commit into actual system calls. Cc: Florian Weimer Cc: Peter Maydell Cc: Andy Lutomirski Suggested-by: Theodore Ts'o Link: https://bugs.launchpad.net/qemu/+bug/1805913 Link: https://lore.kernel.org/lkml/87bm56vqg4.fsf@mid.deneb.enyo.de/ Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=205957 Signed-off-by: Linus Walleij Signed-off-by: Peter Maydell Tested-by: Peter Maydell --- fs/fcntl.c | 4 ++++ include/uapi/linux/fcntl.h | 9 +++++++++ tools/include/uapi/linux/fcntl.h | 9 +++++++++ tools/perf/trace/beauty/fcntl.c | 3 ++- 4 files changed, 24 insertions(+), 1 deletion(-) diff --git a/fs/fcntl.c b/fs/fcntl.c index 2e4c0fa2074b..d194b1265bd4 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -426,6 +426,10 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg, case F_SET_FILE_RW_HINT: err = fcntl_rw_hint(filp, cmd, arg); break; + case F_SET_FILE_32BIT_FS: + filp->f_mode |= FMODE_32BITHASH; + err = 0; + break; default: break; } diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h index ca88b7bce553..b9ad934147e8 100644 --- a/include/uapi/linux/fcntl.h +++ b/include/uapi/linux/fcntl.h @@ -73,6 +73,15 @@ */ #define RWF_WRITE_LIFE_NOT_SET RWH_WRITE_LIFE_NOT_SET +/* + * This instructs the kernel to provide 32bit semantics (such as hashes) from + * the file system layer, when running a userland that depend on 32bit + * semantics on a kernel that supports 64bit userland, but does not use the + * compat ioctl() for e.g. open(), so that the kernel would otherwise assume + * that the userland process is capable of dealing with 64bit semantics. + */ +#define F_SET_FILE_32BIT_FS (F_LINUX_SPECIFIC_BASE + 15) + /* * Types of directory notifications that may be requested. */ diff --git a/tools/include/uapi/linux/fcntl.h b/tools/include/uapi/linux/fcntl.h index ca88b7bce553..b9ad934147e8 100644 --- a/tools/include/uapi/linux/fcntl.h +++ b/tools/include/uapi/linux/fcntl.h @@ -73,6 +73,15 @@ */ #define RWF_WRITE_LIFE_NOT_SET RWH_WRITE_LIFE_NOT_SET +/* + * This instructs the kernel to provide 32bit semantics (such as hashes) from + * the file system layer, when running a userland that depend on 32bit + * semantics on a kernel that supports 64bit userland, but does not use the + * compat ioctl() for e.g. open(), so that the kernel would otherwise assume + * that the userland process is capable of dealing with 64bit semantics. + */ +#define F_SET_FILE_32BIT_FS (F_LINUX_SPECIFIC_BASE + 15) + /* * Types of directory notifications that may be requested. */ diff --git a/tools/perf/trace/beauty/fcntl.c b/tools/perf/trace/beauty/fcntl.c index 56ef83b3d130..da80264678cb 100644 --- a/tools/perf/trace/beauty/fcntl.c +++ b/tools/perf/trace/beauty/fcntl.c @@ -94,7 +94,8 @@ size_t syscall_arg__scnprintf_fcntl_arg(char *bf, size_t size, struct syscall_ar cmd == F_OFD_SETLK || cmd == F_OFD_SETLKW || cmd == F_OFD_GETLK || cmd == F_GETOWN_EX || cmd == F_SETOWN_EX || cmd == F_GET_RW_HINT || cmd == F_SET_RW_HINT || - cmd == F_GET_FILE_RW_HINT || cmd == F_SET_FILE_RW_HINT) + cmd == F_GET_FILE_RW_HINT || cmd == F_SET_FILE_RW_HINT || + cmd == F_SET_FILE_32BIT_FS) return syscall_arg__scnprintf_hex(bf, size, arg); return syscall_arg__scnprintf_long(bf, size, arg);