fork.c: fix NULL pointer dereference when nr_threads == threads-max

I happened to forked lots of processes, and hit NULL pointer dereference.
It is because in copy_process() after checking max_threads, 0 is returned
but not -EAGAIN.

The bug is introduced by "CRED: Detach the credentials from task_struct"
(commit f1752eec6145c97163dbce62d17cf5d928e28a27).

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 242a706e7721..6d5dbb7a13e2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1005,6 +1005,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
          * triggers too late. This doesn't hurt, the check is only there
          * to stop root fork bombs.
          */
+        retval = -EAGAIN;
         if (nr_threads >= max_threads)
                 goto bad_fork_cleanup_count;