4.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Eric Dumazet <[email protected]> [ Upstream commit fd6055a806edc4019be1b9fb7d25262599bca5b1 ] When peeking, if a bad csum is discovered, the skb is unlinked from the queue with __sk_queue_drop_skb and the peek operation restarted. __sk_queue_drop_skb only drops packets that match the queue head. This fails if the skb was found after the head, using SO_PEEK_OFF socket option. This causes an infinite loop. We MUST drop this problematic skb, and we can simply check if skb was already removed by another thread, by looking at skb->next : This pointer is set to NULL by the __skb_unlink() operation, that might have happened only under the spinlock protection. Many thanks to syzkaller team (and particularly Dmitry Vyukov who provided us nice C reproducers exhibiting the lockup) and Willem de Bruijn who provided first version for this patch and a test program. Fixes: 627d2d6b5500 ("udp: enable MSG_PEEK at non-zero offset") Signed-off-by: Eric Dumazet <[email protected]> Reported-by: Dmitry Vyukov <[email protected]> Cc: Willem de Bruijn <[email protected]> Acked-by: Paolo Abeni <[email protected]> Acked-by: Willem de Bruijn <[email protected]> Signed-off-by: David S. Miller <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- net/core/datagram.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -351,7 +351,7 @@ int skb_kill_datagram(struct sock *sk, s if (flags & MSG_PEEK) { err = -ENOENT; spin_lock_bh(&sk->sk_receive_queue.lock); - if (skb == skb_peek(&sk->sk_receive_queue)) { + if (skb->next) { __skb_unlink(skb, &sk->sk_receive_queue); atomic_dec(&skb->users); err = 0;
