From 5cd9c58fbe9ec92b45b27e131719af4f2bd9eb40 Mon Sep 17 00:00:00 2001 From: David Howells Date: Thu, 14 Aug 2008 11:37:28 +0100 Subject: security: Fix setting of PF_SUPERPRIV by __capable() Fix the setting of PF_SUPERPRIV by __capable() as it could corrupt the flags the target process if that is not the current process and it is trying to change its own flags in a different way at the same time. __capable() is using neither atomic ops nor locking to protect t->flags. This patch removes __capable() and introduces has_capability() that doesn't set PF_SUPERPRIV on the process being queried. This patch further splits security_ptrace() in two: (1) security_ptrace_may_access(). This passes judgement on whether one process may access another only (PTRACE_MODE_ATTACH for ptrace() and PTRACE_MODE_READ for /proc), and takes a pointer to the child process. current is the parent. (2) security_ptrace_traceme(). This passes judgement on PTRACE_TRACEME only, and takes only a pointer to the parent process. current is the child. In Smack and commoncap, this uses has_capability() to determine whether the parent will be permitted to use PTRACE_ATTACH if normal checks fail. This does not set PF_SUPERPRIV. Two of the instances of __capable() actually only act on current, and so have been changed to calls to capable(). Of the places that were using __capable(): (1) The OOM killer calls __capable() thrice when weighing the killability of a process. All of these now use has_capability(). (2) cap_ptrace() and smack_ptrace() were using __capable() to check to see whether the parent was allowed to trace any process. As mentioned above, these have been split. For PTRACE_ATTACH and /proc, capable() is now used, and for PTRACE_TRACEME, has_capability() is used. (3) cap_safe_nice() only ever saw current, so now uses capable(). (4) smack_setprocattr() rejected accesses to tasks other than current just after calling __capable(), so the order of these two tests have been switched and capable() is used instead. (5) In smack_file_send_sigiotask(), we need to allow privileged processes to receive SIGIO on files they're manipulating. (6) In smack_task_wait(), we let a process wait for a privileged process, whether or not the process doing the waiting is privileged. I've tested this with the LTP SELinux and syscalls testscripts. Signed-off-by: David Howells Acked-by: Serge Hallyn Acked-by: Casey Schaufler Acked-by: Andrew G. Morgan Acked-by: Al Viro Signed-off-by: James Morris --- include/linux/capability.h | 15 +++++++++++++-- include/linux/security.h | 39 +++++++++++++++++++++++++-------------- 2 files changed, 38 insertions(+), 16 deletions(-) (limited to 'include') diff --git a/include/linux/capability.h b/include/linux/capability.h index 02673846d20..9d1fe30b6f6 100644 --- a/include/linux/capability.h +++ b/include/linux/capability.h @@ -503,8 +503,19 @@ extern const kernel_cap_t __cap_init_eff_set; kernel_cap_t cap_set_effective(const kernel_cap_t pE_new); -int capable(int cap); -int __capable(struct task_struct *t, int cap); +/** + * has_capability - Determine if a task has a superior capability available + * @t: The task in question + * @cap: The capability to be tested for + * + * Return true if the specified task has the given superior capability + * currently in effect, false if not. + * + * Note that this does not set PF_SUPERPRIV on the task. + */ +#define has_capability(t, cap) (security_capable((t), (cap)) == 0) + +extern int capable(int cap); #endif /* __KERNEL__ */ diff --git a/include/linux/security.h b/include/linux/security.h index fd96e7f8a6f..2ee5ecfb239 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -46,8 +46,8 @@ struct audit_krule; */ extern int cap_capable(struct task_struct *tsk, int cap); extern int cap_settime(struct timespec *ts, struct timezone *tz); -extern int cap_ptrace(struct task_struct *parent, struct task_struct *child, - unsigned int mode); +extern int cap_ptrace_may_access(struct task_struct *child, unsigned int mode); +extern int cap_ptrace_traceme(struct task_struct *parent); extern int cap_capget(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted); extern int cap_capset_check(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted); extern void cap_capset_set(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted); @@ -1157,17 +1157,24 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts) * @alter contains the flag indicating whether changes are to be made. * Return 0 if permission is granted. * - * @ptrace: - * Check permission before allowing the @parent process to trace the + * @ptrace_may_access: + * Check permission before allowing the current process to trace the * @child process. * Security modules may also want to perform a process tracing check * during an execve in the set_security or apply_creds hooks of * binprm_security_ops if the process is being traced and its security * attributes would be changed by the execve. - * @parent contains the task_struct structure for parent process. - * @child contains the task_struct structure for child process. + * @child contains the task_struct structure for the target process. * @mode contains the PTRACE_MODE flags indicating the form of access. * Return 0 if permission is granted. + * @ptrace_traceme: + * Check that the @parent process has sufficient permission to trace the + * current process before allowing the current process to present itself + * to the @parent process for tracing. + * The parent process will still have to undergo the ptrace_may_access + * checks before it is allowed to trace this one. + * @parent contains the task_struct structure for debugger process. + * Return 0 if permission is granted. * @capget: * Get the @effective, @inheritable, and @permitted capability sets for * the @target process. The hook may also perform permission checking to @@ -1287,8 +1294,8 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts) struct security_operations { char name[SECURITY_NAME_MAX + 1]; - int (*ptrace) (struct task_struct *parent, struct task_struct *child, - unsigned int mode); + int (*ptrace_may_access) (struct task_struct *child, unsigned int mode); + int (*ptrace_traceme) (struct task_struct *parent); int (*capget) (struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, kernel_cap_t *permitted); @@ -1560,8 +1567,8 @@ extern struct dentry *securityfs_create_dir(const char *name, struct dentry *par extern void securityfs_remove(struct dentry *dentry); /* Security operations */ -int security_ptrace(struct task_struct *parent, struct task_struct *child, - unsigned int mode); +int security_ptrace_may_access(struct task_struct *child, unsigned int mode); +int security_ptrace_traceme(struct task_struct *parent); int security_capget(struct task_struct *target, kernel_cap_t *effective, kernel_cap_t *inheritable, @@ -1742,11 +1749,15 @@ static inline int security_init(void) return 0; } -static inline int security_ptrace(struct task_struct *parent, - struct task_struct *child, - unsigned int mode) +static inline int security_ptrace_may_access(struct task_struct *child, + unsigned int mode) +{ + return cap_ptrace_may_access(child, mode); +} + +static inline int security_ptrace_traceme(struct task_struct *child) { - return cap_ptrace(parent, child, mode); + return cap_ptrace_traceme(parent); } static inline int security_capget(struct task_struct *target, -- cgit v1.2.3-70-g09d2