signals: move cred_guard_mutex from task_struct to signal_struct

Oleg Nesterov pointed out we have to prevent multiple-threads-inside-exec
itself and we can reuse ->cred_guard_mutex for it.  Yes, concurrent
execve() has no worth.

Let's move ->cred_guard_mutex from task_struct to signal_struct.  It
naturally prevent multiple-threads-inside-exec.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 3aa75b8888a1..9722909c4d88 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1083,14 +1083,14 @@ EXPORT_SYMBOL(setup_new_exec);
  */
 int prepare_bprm_creds(struct linux_binprm *bprm)
 {
-        if (mutex_lock_interruptible(&current->cred_guard_mutex))
+        if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
                 return -ERESTARTNOINTR;
 
         bprm->cred = prepare_exec_creds();
         if (likely(bprm->cred))
                 return 0;
 
-        mutex_unlock(&current->cred_guard_mutex);
+        mutex_unlock(&current->signal->cred_guard_mutex);
         return -ENOMEM;
 }
 
@@ -1098,7 +1098,7 @@ void free_bprm(struct linux_binprm *bprm)
 {
         free_arg_pages(bprm);
         if (bprm->cred) {
-                mutex_unlock(&current->cred_guard_mutex);
+                mutex_unlock(&current->signal->cred_guard_mutex);
                 abort_creds(bprm->cred);
         }
         kfree(bprm);
@@ -1119,13 +1119,13 @@ void install_exec_creds(struct linux_binprm *bprm)
          * credentials; any time after this it may be unlocked.
          */
         security_bprm_committed_creds(bprm);
-        mutex_unlock(&current->cred_guard_mutex);
+        mutex_unlock(&current->signal->cred_guard_mutex);
 }
 EXPORT_SYMBOL(install_exec_creds);
 
 /*
  * determine how safe it is to execute the proposed program
- * - the caller must hold current->cred_guard_mutex to protect against
+ * - the caller must hold ->cred_guard_mutex to protect against
  *   PTRACE_ATTACH
  */
 int check_unsafe_exec(struct linux_binprm *bprm)