tcp: must unclone packets before mangling them (c52e2421) · Commits · 戴 / test

TCP stack should make sure it owns skbs before mangling them. We had various crashes using bnx2x, and it turned out gso_size was cleared right before bnx2x driver was populating TC descriptor of the _previous_ packet send. TCP stack can sometime retransmit packets that are still in Qdisc. Of course we could make bnx2x driver more robust (using ACCESS_ONCE(shinfo->gso_size) for example), but the bug is TCP stack. We have identified two points where skb_unclone() was needed. This patch adds a WARN_ON_ONCE() to warn us if we missed another fix of this kind. Kudos to Neal for finding the root cause of this bug. Its visible using small MSS. Signed-off-by:

Eric Dumazet <edumazet@google.com> Signed-off-by:

Neal Cardwell <ncardwell@google.com> Cc: Yuchung Cheng <ycheng@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/ipv4/tcp_output.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -986,6 +986,9 @@ static void tcp_queue_skb(struct sock sk, struct sk_buff skb)
		static void tcp_set_skb_tso_segs(const struct sock sk, struct sk_buff skb,
		unsigned int mss_now)
		{
		/* Make sure we own this skb before messing gso_size/gso_segs */
		WARN_ON_ONCE(skb_cloned(skb));

		if (skb->len <= mss_now \|\| !sk_can_gso(sk) \|\|
		skb->ip_summed == CHECKSUM_NONE) {
		/* Avoid the costly divide in the normal
		@@ -1067,9 +1070,7 @@ int tcp_fragment(struct sock sk, struct sk_buff skb, u32 len,
		if (nsize < 0)
		nsize = 0;

		if (skb_cloned(skb) &&
		skb_is_nonlinear(skb) &&
		pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
		if (skb_unclone(skb, GFP_ATOMIC))
		return -ENOMEM;

		/* Get a new skb... force flag on. */
		@@ -2344,6 +2345,8 @@ int __tcp_retransmit_skb(struct sock sk, struct sk_buff skb)
		int oldpcount = tcp_skb_pcount(skb);

		if (unlikely(oldpcount > 1)) {
		if (skb_unclone(skb, GFP_ATOMIC))
		return -ENOMEM;
		tcp_init_tso_segs(sk, skb, cur_mss);
		tcp_adjust_pcount(sk, skb, oldpcount - tcp_skb_pcount(skb));
		}

Admin message