Commit 1e39e5c6 authored by Eric Dumazet's avatar Eric Dumazet Committed by Greg Kroah-Hartman

udp: on peeking bad csum, drop packets even if not at head


[ Upstream commit fd6055a8 ]

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: 627d2d6b ("udp: enable MSG_PEEK at non-zero offset")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Acked-by: default avatarPaolo Abeni <pabeni@redhat.com>
Acked-by: default avatarWillem de Bruijn <willemb@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 4b4a194a
......@@ -351,7 +351,7 @@ int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags)
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;
......
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