Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull pid allocation bug fix from Eric Biederman:
 "The replacement of the pid hash table and the pid bitmap with an idr
  resulted in an implementation that now fails more often in low memory
  situations. Allowing fuzzers to observe bad behavior from a memory
  allocation failure during pid allocation.

  This is a small change to fix this by making the kernel more robust in
  the case of error. The non-error paths are left alone so the only
  danger is to the already broken error path. I have manually injected
  errors and verified that this new error handling works"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  pid: Handle failure to allocate the first pid in a pid namespace

1 files changed, 5 insertions, 3 deletions

diff --git a/kernel/pid.c b/kernel/pid.c
index b13b624e2c4902..1e8bb6550ec4bf 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -193,10 +193,8 @@ struct pid *alloc_pid(struct pid_namespace *ns)
 	}
 
 	if (unlikely(is_child_reaper(pid))) {
-		if (pid_ns_prepare_proc(ns)) {
-			disable_pid_allocation(ns);
+		if (pid_ns_prepare_proc(ns))
 			goto out_free;
-		}
 	}
 
 	get_pid_ns(ns);
@@ -226,6 +224,10 @@ out_free:
 	while (++i <= ns->level)
 		idr_remove(&ns->idr, (pid->numbers + i)->nr);
 
+	/* On failure to allocate the first pid, reset the state */
+	if (ns->pid_allocated == PIDNS_ADDING)
+		idr_set_cursor(&ns->idr, 0);
+
 	spin_unlock_irq(&pidmap_lock);
 
 	kmem_cache_free(ns->pid_cachep, pid);