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, 4 insertions, 4 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9b094c1c8465..f3d02ca461ec 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -226,7 +226,7 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
 {
         struct mm_struct *mm;
 
-        if (mutex_lock_killable(&task->cred_guard_mutex))
+        if (mutex_lock_killable(&task->signal->cred_guard_mutex))
                 return NULL;
 
         mm = get_task_mm(task);
@@ -235,7 +235,7 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
                 mmput(mm);
                 mm = NULL;
         }
-        mutex_unlock(&task->cred_guard_mutex);
+        mutex_unlock(&task->signal->cred_guard_mutex);
 
         return mm;
 }
@@ -2354,14 +2354,14 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
                 goto out_free;
 
         /* Guard against adverse ptrace interaction */
-        length = mutex_lock_interruptible(&task->cred_guard_mutex);
+        length = mutex_lock_interruptible(&task->signal->cred_guard_mutex);
         if (length < 0)
                 goto out_free;
 
         length = security_setprocattr(task,
                                       (char*)file->f_path.dentry->d_name.name,
                                       (void*)page, count);
-        mutex_unlock(&task->cred_guard_mutex);
+        mutex_unlock(&task->signal->cred_guard_mutex);
 out_free:
         free_page((unsigned long) page);
 out: