io_uring: avoid null-ptr-deref in io_arm_poll_handler

No upstream commit exists for this commit.

The issue was introduced with backporting upstream commit c16bda37594f
("io_uring/poll: allow some retries for poll triggering spuriously").

Memory allocation can possibly fail causing invalid pointer be
dereferenced just before comparing it to NULL value.

Move the pointer check in proper place (upstream has the similar location
of the check). In case the request has REQ_F_POLLED flag up, apoll can't
be NULL so no need to check there.

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 445afda927f47a6240a9c6f4539cfaa0d353d21d..fd799567fc23a8ab9e9b901e51f9e7b124fb15d2 100644 (file)
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -5792,10 +5792,10 @@ static int io_arm_poll_handler(struct io_kiocb *req)
                }
        } else {
                apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC);
+               if (unlikely(!apoll))
+                       return IO_APOLL_ABORTED;
                apoll->poll.retries = APOLL_MAX_RETRY;
        }
-       if (unlikely(!apoll))
-               return IO_APOLL_ABORTED;
        apoll->double_poll = NULL;
        req->apoll = apoll;
        req->flags |= REQ_F_POLLED;