proc: make proc_fd_permission() thread-friendly
authorOleg Nesterov <oleg@redhat.com>
Wed, 11 Sep 2013 21:24:37 +0000 (14:24 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 11 Sep 2013 22:59:03 +0000 (15:59 -0700)
proc_fd_permission() says "process can still access /proc/self/fd after it
has executed a setuid()", but the "task_pid() = proc_pid() check only
helps if the task is group leader, /proc/self points to
/proc/<leader-pid>.

Change this check to use task_tgid() so that the whole thread group can
access its /proc/self/fd or /proc/<tid-of-sub-thread>/fd.

Notes:
- CLONE_THREAD does not require CLONE_FILES so task->files
  can differ, but I don't think this can lead to any security
  problem. And this matches same_thread_group() in
  __ptrace_may_access().

- /proc/self should probably point to /proc/<thread-tid>, but
  it is too late to change the rules. Perhaps it makes sense
  to add /proc/thread though.

Test-case:

void *tfunc(void *arg)
{
assert(opendir("/proc/self/fd"));
return NULL;
}

int main(void)
{
pthread_t t;
pthread_create(&t, NULL, tfunc, NULL);
pthread_join(t, NULL);
return 0;
}

fails if, say, this executable is not readable and suid_dumpable = 0.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs/proc/fd.c

index 0ff80f9b930f7226124e670c2814d7f4618d4532..985ea881b5bc489aa7ae0657e23fbe23d650d844 100644 (file)
@@ -286,7 +286,7 @@ int proc_fd_permission(struct inode *inode, int mask)
        int rv = generic_permission(inode, mask);
        if (rv == 0)
                return 0;
-       if (task_pid(current) == proc_pid(inode))
+       if (task_tgid(current) == proc_pid(inode))
                rv = 0;
        return rv;
 }