epoll: remember the event if epoll_wait returns -EFAULT

If epoll_wait returns -EFAULT, the event that was being returned when the
fault was encountered will be forgotten.  This is not a big deal since
EFAULT will happen only if a buggy userspace program passes in a bad
address, in which case what happens later usually doesn't matter.
However, it is easy to remember the event for later, and this patch makes
a simple change to do that.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index db4365f8a75c..c806a0c4383c 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1054,8 +1054,10 @@ static int ep_send_events_proc(struct eventpoll *ep, struct list_head *head,
                  */
                 if (revents) {
                         if (__put_user(revents, &uevent->events) ||
-                            __put_user(epi->event.data, &uevent->data))
+                            __put_user(epi->event.data, &uevent->data)) {
+                                list_add(&epi->rdllink, head);
                                 return eventcnt ? eventcnt : -EFAULT;
+                        }
                         eventcnt++;
                         uevent++;
                         if (epi->event.events & EPOLLONESHOT)