[PATCH 2/3] userfaultfd: non-cooperative: robustness check

[Andrea Arcangeli <aarcange@redhat.com>]

Similar to the handle_userfault() case, also make sure to never
attempt to send any event past the PF_EXITING point of no return.

This is purely a robustness check.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
 fs/userfaultfd.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 52733a7..3d7c248 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -529,8 +529,13 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason)
 static int userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
 					     struct userfaultfd_wait_queue *ewq)
 {
-	int ret = 0;
+	int ret;
+
+	ret = -1;
+	if (WARN_ON_ONCE(current->flags & PF_EXITING))
+		goto out;
 
+	ret = 0;
 	ewq->ctx = ctx;
 	init_waitqueue_entry(&ewq->wq, current);
 
@@ -565,7 +570,7 @@ static int userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
 	 * ctx may go away after this if the userfault pseudo fd is
 	 * already released.
 	 */
-
+out:
 	userfaultfd_ctx_put(ctx);
 	return ret;
 }

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