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Hermes SMTP Server) with ESMTPA ID b58a5884cc254441b7169bc1ab603d8d; Fri, 28 Apr 2023 20:28:34 +0000 (UTC) From: Casey Schaufler To: casey@schaufler-ca.com, paul@paul-moore.com, linux-security-module@vger.kernel.org Cc: jmorris@namei.org, keescook@chromium.org, john.johansen@canonical.com, penguin-kernel@i-love.sakura.ne.jp, stephen.smalley.work@gmail.com, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, mic@digikod.net Subject: [PATCH v10 04/11] LSM: syscalls for current process attributes Date: Fri, 28 Apr 2023 13:26:44 -0700 Message-Id: <20230428202651.159828-5-casey@schaufler-ca.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230428202651.159828-1-casey@schaufler-ca.com> References: <20230428202651.159828-1-casey@schaufler-ca.com> MIME-Version: 1.0 Precedence: bulk List-ID: Create a system call lsm_get_self_attr() to provide the security module maintained attributes of the current process. Create a system call lsm_set_self_attr() to set a security module maintained attribute of the current process. Historically these attributes have been exposed to user space via entries in procfs under /proc/self/attr. The attribute value is provided in a lsm_ctx structure. The structure identifies the size of the attribute, and the attribute value. The format of the attribute value is defined by the security module. A flags field is included for LSM specific information. It is currently unused and must be 0. The total size of the data, including the lsm_ctx structure and any padding, is maintained as well. struct lsm_ctx { __u64 id; __u64 flags; __u64 len; __u64 ctx_len; __u8 ctx[]; }; Two new LSM hooks are used to interface with the LSMs. security_getselfattr() collects the lsm_ctx values from the LSMs that support the hook, accounting for space requirements. security_setselfattr() identifies which LSM the attribute is intended for and passes it along. Signed-off-by: Casey Schaufler Reviewed-by: Kees Cook --- Documentation/userspace-api/lsm.rst | 15 ++++ include/linux/lsm_hook_defs.h | 4 + include/linux/lsm_hooks.h | 9 +++ include/linux/security.h | 19 +++++ include/linux/syscalls.h | 5 ++ include/uapi/linux/lsm.h | 36 +++++++++ kernel/sys_ni.c | 4 + security/Makefile | 1 + security/lsm_syscalls.c | 55 ++++++++++++++ security/security.c | 112 ++++++++++++++++++++++++++++ 10 files changed, 260 insertions(+) create mode 100644 security/lsm_syscalls.c diff --git a/Documentation/userspace-api/lsm.rst b/Documentation/userspace-api/lsm.rst index 6ddf5506110b..e6c3f262addc 100644 --- a/Documentation/userspace-api/lsm.rst +++ b/Documentation/userspace-api/lsm.rst @@ -48,6 +48,21 @@ creating socket objects. The proc filesystem provides this value in ``/proc/self/attr/sockcreate``. This is supported by the SELinux security module. +Kernel interface +================ + +Set a security attribute of the current process +----------------------------------------------- + +.. kernel-doc:: security/lsm_syscalls.c + :identifiers: sys_lsm_set_self_attr + +Get the specified security attributes of the current process +------------------------------------------------------------ + +.. kernel-doc:: security/lsm_syscalls.c + :identifiers: sys_lsm_get_self_attr + Additional documentation ======================== diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h index 094b76dc7164..32104ff61999 100644 --- a/include/linux/lsm_hook_defs.h +++ b/include/linux/lsm_hook_defs.h @@ -261,6 +261,10 @@ LSM_HOOK(int, 0, sem_semop, struct kern_ipc_perm *perm, struct sembuf *sops, LSM_HOOK(int, 0, netlink_send, struct sock *sk, struct sk_buff *skb) LSM_HOOK(void, LSM_RET_VOID, d_instantiate, struct dentry *dentry, struct inode *inode) +LSM_HOOK(int, -EOPNOTSUPP, getselfattr, unsigned int attr, + struct lsm_ctx __user *ctx, size_t *size, u32 flags) +LSM_HOOK(int, -EOPNOTSUPP, setselfattr, unsigned int attr, + struct lsm_ctx __user *ctx, size_t size, u32 flags) LSM_HOOK(int, -EINVAL, getprocattr, struct task_struct *p, const char *name, char **value) LSM_HOOK(int, -EINVAL, setprocattr, const char *name, void *value, size_t size) diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index c1f00d09033e..457ff953e331 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -25,6 +25,7 @@ #ifndef __LINUX_LSM_HOOKS_H #define __LINUX_LSM_HOOKS_H +#include #include #include #include @@ -503,6 +504,14 @@ * and writing the xattrs as this hook is merely a filter. * @d_instantiate: * Fill in @inode security information for a @dentry if allowed. + * @getselfattr: + * Read attribute @attr for the current process and store it into @ctx. + * Return 0 on success, -EOPNOTSUPP if the attribute is not supported, + * or another negative value otherwise. + * @setselfattr: + * Set attribute @attr for the current process. + * Return 0 on success, -EOPNOTSUPP if the attribute is not supported, + * or another negative value otherwise. * @getprocattr: * Read attribute @name for process @p and store it into @value if allowed. * Return the length of @value on success, a negative value otherwise. diff --git a/include/linux/security.h b/include/linux/security.h index 8faed81fc3b4..806bff425af9 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -60,6 +60,7 @@ struct fs_parameter; enum fs_value_type; struct watch; struct watch_notification; +struct lsm_ctx; /* Default (no) options for the capable function */ #define CAP_OPT_NONE 0x0 @@ -473,6 +474,10 @@ int security_sem_semctl(struct kern_ipc_perm *sma, int cmd); int security_sem_semop(struct kern_ipc_perm *sma, struct sembuf *sops, unsigned nsops, int alter); void security_d_instantiate(struct dentry *dentry, struct inode *inode); +int security_getselfattr(unsigned int attr, struct lsm_ctx __user *ctx, + size_t __user *size, u32 flags); +int security_setselfattr(unsigned int attr, struct lsm_ctx __user *ctx, + size_t size, u32 flags); int security_getprocattr(struct task_struct *p, int lsmid, const char *name, char **value); int security_setprocattr(int lsmid, const char *name, void *value, size_t size); @@ -1343,6 +1348,20 @@ static inline void security_d_instantiate(struct dentry *dentry, struct inode *inode) { } +static inline int security_getselfattr(unsigned int attr, + struct lsm_ctx __user *ctx, + size_t __user *size, u32 flags) +{ + return -EOPNOTSUPP; +} + +static inline int security_setselfattr(unsigned int attr, + struct lsm_ctx __user *ctx, + size_t size, u32 flags) +{ + return -EOPNOTSUPP; +} + static inline int security_getprocattr(struct task_struct *p, int lsmid, const char *name, char **value) { diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 33a0ee3bcb2e..9a94c31bf6b6 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -71,6 +71,7 @@ struct clone_args; struct open_how; struct mount_attr; struct landlock_ruleset_attr; +struct lsm_ctx; enum landlock_rule_type; #include @@ -1058,6 +1059,10 @@ asmlinkage long sys_memfd_secret(unsigned int flags); asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len, unsigned long home_node, unsigned long flags); +asmlinkage long sys_lsm_get_self_attr(unsigned int attr, struct lsm_ctx *ctx, + size_t *size, __u32 flags); +asmlinkage long sys_lsm_set_self_attr(unsigned int attr, struct lsm_ctx *ctx, + size_t size, __u32 flags); /* * Architecture-specific system calls diff --git a/include/uapi/linux/lsm.h b/include/uapi/linux/lsm.h index f27c9a9cc376..eeda59a77c02 100644 --- a/include/uapi/linux/lsm.h +++ b/include/uapi/linux/lsm.h @@ -9,6 +9,36 @@ #ifndef _UAPI_LINUX_LSM_H #define _UAPI_LINUX_LSM_H +#include +#include + +/** + * struct lsm_ctx - LSM context information + * @id: the LSM id number, see LSM_ID_XXX + * @flags: LSM specific flags + * @len: length of the lsm_ctx struct, @ctx and any other data or padding + * @ctx_len: the size of @ctx + * @ctx: the LSM context value + * + * The @len field MUST be equal to the size of the lsm_ctx struct + * plus any additional padding and/or data placed after @ctx. + * + * In all cases @ctx_len MUST be equal to the length of @ctx. + * If @ctx is a string value it should be nul terminated with + * @ctx_len equal to `strlen(@ctx) + 1`. Binary values are + * supported. + * + * The @flags and @ctx fields SHOULD only be interpreted by the + * LSM specified by @id; they MUST be set to zero/0 when not used. + */ +struct lsm_ctx { + __u64 id; + __u64 flags; + __u64 len; + __u64 ctx_len; + __u8 ctx[]; +}; + /* * ID tokens to identify Linux Security Modules (LSMs) * @@ -51,4 +81,10 @@ #define LSM_ATTR_PREV 104 #define LSM_ATTR_SOCKCREATE 105 +/* + * LSM_FLAG_XXX definitions identify special handling instructions + * for the API. + */ +#define LSM_FLAG_SINGLE 0x0001 + #endif /* _UAPI_LINUX_LSM_H */ diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 860b2dcf3ac4..d03c78ef1562 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -262,6 +262,10 @@ COND_SYSCALL_COMPAT(recvmsg); /* mm/nommu.c, also with MMU */ COND_SYSCALL(mremap); +/* security/lsm_syscalls.c */ +COND_SYSCALL(lsm_get_self_attr); +COND_SYSCALL(lsm_set_self_attr); + /* security/keys/keyctl.c */ COND_SYSCALL(add_key); COND_SYSCALL(request_key); diff --git a/security/Makefile b/security/Makefile index 18121f8f85cd..59f238490665 100644 --- a/security/Makefile +++ b/security/Makefile @@ -7,6 +7,7 @@ obj-$(CONFIG_KEYS) += keys/ # always enable default capabilities obj-y += commoncap.o +obj-$(CONFIG_SECURITY) += lsm_syscalls.o obj-$(CONFIG_MMU) += min_addr.o # Object file lists diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c new file mode 100644 index 000000000000..ee3881159241 --- /dev/null +++ b/security/lsm_syscalls.c @@ -0,0 +1,55 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * System calls implementing the Linux Security Module API. + * + * Copyright (C) 2022 Casey Schaufler + * Copyright (C) 2022 Intel Corporation + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/** + * sys_lsm_set_self_attr - Set current task's security module attribute + * @attr: which attribute to set + * @ctx: the LSM contexts + * @size: size of @ctx + * @flags: reserved for future use + * + * Sets the calling task's LSM context. On success this function + * returns 0. If the attribute specified cannot be set a negative + * value indicating the reason for the error is returned. + */ +SYSCALL_DEFINE4(lsm_set_self_attr, unsigned int, attr, struct lsm_ctx __user *, + ctx, size_t, size, u32, flags) +{ + return security_setselfattr(attr, ctx, size, flags); +} + +/** + * sys_lsm_get_self_attr - Return current task's security module attributes + * @attr: which attribute to set + * @ctx: the LSM contexts + * @size: size of @ctx, updated on return + * @flags: reserved for future use + * + * Returns the calling task's LSM contexts. On success this + * function returns the number of @ctx array elements. This value + * may be zero if there are no LSM contexts assigned. If @size is + * insufficient to contain the return data -E2BIG is returned and + * @size is set to the minimum required size. In all other cases + * a negative value indicating the error is returned. + */ +SYSCALL_DEFINE4(lsm_get_self_attr, unsigned int, attr, struct lsm_ctx __user *, + ctx, size_t __user *, size, u32, flags) +{ + return security_getselfattr(attr, ctx, size, flags); +} diff --git a/security/security.c b/security/security.c index 5a48b1b539e5..94b78bfd06b9 100644 --- a/security/security.c +++ b/security/security.c @@ -2176,6 +2176,118 @@ void security_d_instantiate(struct dentry *dentry, struct inode *inode) } EXPORT_SYMBOL(security_d_instantiate); +/** + * security_getselfattr - Read an LSM attribute of the current process. + * @attr: which attribute to return + * @ctx: the user-space destination for the information, or NULL + * @size: the size of space available to receive the data + * @flags: special handling options. LSM_FLAG_SINGLE indicates that only + * attributes associated with the LSM identified in the passed @ctx be + * reported + * + * Returns the number of attributes found on success, negative value + * on error. @size is reset to the total size of the data. + * If @size is insufficient to contain the data -E2BIG is returned. + */ +int security_getselfattr(unsigned int attr, struct lsm_ctx __user *ctx, + size_t __user *size, u32 flags) +{ + struct security_hook_list *hp; + struct lsm_ctx lctx = { .id = LSM_ID_UNDEF, }; + u8 __user *base = (u8 __user *)ctx; + size_t total = 0; + size_t entrysize; + size_t left; + bool toobig = false; + int count = 0; + int rc; + + if (attr == 0) + return -EINVAL; + if (size == NULL) + return -EINVAL; + if (get_user(left, size)) + return -EFAULT; + + if ((flags & LSM_FLAG_SINGLE) == LSM_FLAG_SINGLE) { + if (!ctx) + return -EINVAL; + if (copy_struct_from_user(&lctx, sizeof(lctx), ctx, left)) + return -EFAULT; + if (lctx.id == LSM_ID_UNDEF) + return -EINVAL; + } else if (flags) { + return -EINVAL; + } + + hlist_for_each_entry(hp, &security_hook_heads.getselfattr, list) { + if (lctx.id != LSM_ID_UNDEF && lctx.id != hp->lsmid->id) + continue; + entrysize = left; + if (base) + ctx = (struct lsm_ctx __user *)(base + total); + rc = hp->hook.getselfattr(attr, ctx, &entrysize, flags); + if (rc == -EOPNOTSUPP) { + rc = 0; + continue; + } + if (rc == -E2BIG) { + toobig = true; + left = 0; + continue; + } + if (rc < 0) + return rc; + + left -= entrysize; + total += entrysize; + count += rc; + } + if (put_user(total, size)) + return -EFAULT; + if (toobig) + return -E2BIG; + if (count == 0) + return LSM_RET_DEFAULT(getselfattr); + return count; +} + +/** + * security_setselfattr - Set an LSM attribute on the current process. + * @attr: which attribute to set + * @ctx: the user-space source for the information + * @size: the size of the data + * @flags: reserved for future use, must be 0 + * + * Set an LSM attribute for the current process. The LSM, attribute + * and new value are included in @ctx. + * + * Returns 0 on success, -EINVAL if the input is inconsistent, -EFAULT + * if the user buffer is inaccessible or an LSM specific failure. + */ +int security_setselfattr(unsigned int attr, struct lsm_ctx __user *ctx, + size_t size, u32 flags) +{ + struct security_hook_list *hp; + struct lsm_ctx lctx; + + if (flags) + return -EINVAL; + if (size < sizeof(*ctx)) + return -EINVAL; + if (copy_from_user(&lctx, ctx, sizeof(*ctx))) + return -EFAULT; + if (size < lctx.len || size < lctx.ctx_len + sizeof(ctx) || + lctx.len < lctx.ctx_len + sizeof(ctx)) + return -EINVAL; + + hlist_for_each_entry(hp, &security_hook_heads.setselfattr, list) + if ((hp->lsmid->id) == lctx.id) + return hp->hook.setselfattr(attr, ctx, size, flags); + + return LSM_RET_DEFAULT(setselfattr); +} + int security_getprocattr(struct task_struct *p, int lsmid, const char *name, char **value) {