From 35d59efd105b3b7c1b5878dcc9d1749f41f9740f Mon Sep 17 00:00:00 2001 From: Herbert Xu Date: Wed, 17 Aug 2005 12:03:59 -0700 Subject: [PATCH] [TCP]: Fix bug #5070: kernel BUG at net/ipv4/tcp_output.c:864 1) We send out a normal sized packet with TSO on to start off. 2) ICMP is received indicating a smaller MTU. 3) We send the current sk_send_head which needs to be fragmented since it was created before the ICMP event. The first fragment is then sent out. At this point the remaining fragment is allocated by tcp_fragment. However, its size is padded to fit the L1 cache-line size therefore creating tail-room up to 124 bytes long. This fragment will also be sitting at sk_send_head. 4) tcp_sendmsg is called again and it stores data in the tail-room of of the fragment. 5) tcp_push_one is called by tcp_sendmsg which then calls tso_fragment since the packet as a whole exceeds the MTU. At this point we have a packet that has data in the head area being fed to tso_fragment which bombs out. My take on this is that we shouldn't ever call tcp_fragment on a TSO socket for a packet that is yet to be transmitted since this creates a packet on sk_send_head that cannot be extended. So here is a patch to change it so that tso_fragment is always used in this case. Signed-off-by: Herbert Xu Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 39 ++++++++++++++++++++------------------- 1 file changed, 20 insertions(+), 19 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 3ed6fc15815b..566045e58437 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -861,7 +861,8 @@ static int tso_fragment(struct sock *sk, struct sk_buff *skb, unsigned int len, u16 flags; /* All of a TSO frame must be composed of paged data. */ - BUG_ON(skb->len != skb->data_len); + if (skb->len != skb->data_len) + return tcp_fragment(sk, skb, len, mss_now); buff = sk_stream_alloc_pskb(sk, 0, 0, GFP_ATOMIC); if (unlikely(buff == NULL)) @@ -974,6 +975,8 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle) sent_pkts = 0; while ((skb = sk->sk_send_head)) { + unsigned int limit; + tso_segs = tcp_init_tso_segs(sk, skb, mss_now); BUG_ON(!tso_segs); @@ -994,9 +997,10 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle) break; } + limit = mss_now; if (tso_segs > 1) { - u32 limit = tcp_window_allows(tp, skb, - mss_now, cwnd_quota); + limit = tcp_window_allows(tp, skb, + mss_now, cwnd_quota); if (skb->len < limit) { unsigned int trim = skb->len % mss_now; @@ -1004,15 +1008,12 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle) if (trim) limit = skb->len - trim; } - if (skb->len > limit) { - if (tso_fragment(sk, skb, limit, mss_now)) - break; - } - } else if (unlikely(skb->len > mss_now)) { - if (unlikely(tcp_fragment(sk, skb, mss_now, mss_now))) - break; } + if (skb->len > limit && + unlikely(tso_fragment(sk, skb, limit, mss_now))) + break; + TCP_SKB_CB(skb)->when = tcp_time_stamp; if (unlikely(tcp_transmit_skb(sk, skb_clone(skb, GFP_ATOMIC)))) @@ -1064,11 +1065,14 @@ void tcp_push_one(struct sock *sk, unsigned int mss_now) cwnd_quota = tcp_snd_test(sk, skb, mss_now, TCP_NAGLE_PUSH); if (likely(cwnd_quota)) { + unsigned int limit; + BUG_ON(!tso_segs); + limit = mss_now; if (tso_segs > 1) { - u32 limit = tcp_window_allows(tp, skb, - mss_now, cwnd_quota); + limit = tcp_window_allows(tp, skb, + mss_now, cwnd_quota); if (skb->len < limit) { unsigned int trim = skb->len % mss_now; @@ -1076,15 +1080,12 @@ void tcp_push_one(struct sock *sk, unsigned int mss_now) if (trim) limit = skb->len - trim; } - if (skb->len > limit) { - if (unlikely(tso_fragment(sk, skb, limit, mss_now))) - return; - } - } else if (unlikely(skb->len > mss_now)) { - if (unlikely(tcp_fragment(sk, skb, mss_now, mss_now))) - return; } + if (skb->len > limit && + unlikely(tso_fragment(sk, skb, limit, mss_now))) + return; + /* Send it out now. */ TCP_SKB_CB(skb)->when = tcp_time_stamp; -- 2.30.2