Patch "exec: avoid RLIMIT_STACK races with prlimit()" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

exec: avoid RLIMIT_STACK races with prlimit()

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
exec-avoid-rlimit_stack-races-with-prlimit.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Kees Cook <[email protected]>
Date: Wed, 29 Nov 2017 16:10:51 -0800
Subject: exec: avoid RLIMIT_STACK races with prlimit()

From: Kees Cook <[email protected]>

commit 04e35f4495dd560db30c25efca4eecae8ec8c375 upstream.

While the defense-in-depth RLIMIT_STACK limit on setuid processes was protected against races from other threads calling setrlimit(), I missed protecting it against races from external processes calling prlimit(). This adds locking around the change and makes sure that rlim_max is set too.

---
 fs/exec.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

@@ -1340,10 +1340,15 @@ void setup_new_exec(struct linux_binprm
 		 * avoid bad behavior from the prior rlimits. This has to
 		 * happen before arch_pick_mmap_layout(), which examines
 		 * RLIMIT_STACK, but after the point of no return to avoid
-		 * needing to clean up the change on failure.
+		 * races from other threads changing the limits. This also
+		 * must be protected from races with prlimit() calls.
 		 */
+		task_lock(current->group_leader);
 		if (current->signal->rlim[RLIMIT_STACK].rlim_cur > _STK_LIM)
 			current->signal->rlim[RLIMIT_STACK].rlim_cur = _STK_LIM;
+		if (current->signal->rlim[RLIMIT_STACK].rlim_max > _STK_LIM)
+			current->signal->rlim[RLIMIT_STACK].rlim_max = _STK_LIM;
+		task_unlock(current->group_leader);
 	}
 
 	arch_pick_mmap_layout(current->mm);

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/exec-avoid-rlimit_stack-races-with-prlimit.patch