path: root/kernel/capability.c
diff options
authorDavid Howells <>2008-08-14 10:37:28 (GMT)
committerJames Morris <>2008-08-14 12:59:43 (GMT)
commit5cd9c58fbe9ec92b45b27e131719af4f2bd9eb40 (patch)
tree8573db001b4dc3c2ad97102dda42b841c40b5f6c /kernel/capability.c
parent8d0968abd03ec6b407df117adc773562386702fa (diff)
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 <>
Diffstat (limited to 'kernel/capability.c')
1 files changed, 13 insertions, 8 deletions
diff --git a/kernel/capability.c b/kernel/capability.c
index 0101e84..33e51e7 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -486,17 +486,22 @@ asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
return ret;
-int __capable(struct task_struct *t, int cap)
+ * capable - Determine if the current task has a superior capability in effect
+ * @cap: The capability to be tested for
+ *
+ * Return true if the current task has the given superior capability currently
+ * available for use, false if not.
+ *
+ * This sets PF_SUPERPRIV on the task if the capability is available on the
+ * assumption that it's about to be used.
+ */
+int capable(int cap)
- if (security_capable(t, cap) == 0) {
- t->flags |= PF_SUPERPRIV;
+ if (has_capability(current, cap)) {
+ current->flags |= PF_SUPERPRIV;
return 1;
return 0;
-int capable(int cap)
- return __capable(current, cap);