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authorHerbert Xu <herbert@gondor.apana.org.au>2008-12-25 17:12:58 -0800
committerDavid S. Miller <davem@davemloft.net>2008-12-25 17:12:58 -0800
commit64ff3b938ec6782e6585a83d5459b98b0c3f6eb8 (patch)
treeaa53a121fd7edb8ba5b3fede8ff1990b44265d56 /net
parent8510b937ae1e23583abdeb828cad5c518295c61d (diff)
downloadlinux-2.6.34-ux500-64ff3b938ec6782e6585a83d5459b98b0c3f6eb8.tar.gz
tcp: Always set urgent pointer if it's beyond snd_nxt
Our TCP stack does not set the urgent flag if the urgent pointer does not fit in 16 bits, i.e., if it is more than 64K from the sequence number of a packet. This behaviour is different from the BSDs, and clearly contradicts the purpose of urgent mode, which is to send the notification (though not necessarily the associated data) as soon as possible. Our current behaviour may in fact delay the urgent notification indefinitely if the receiver window does not open up. Simply matching BSD however may break legacy applications which incorrectly rely on the out-of-band delivery of urgent data, and conversely the in-band delivery of non-urgent data. Alexey Kuznetsov suggested a safe solution of following BSD only if the urgent pointer itself has not yet been transmitted. This way we guarantee that when the remote end sees the packet with non-urgent data marked as urgent due to wrap-around we would have advanced the urgent pointer beyond, either to the actual urgent data or to an as-yet untransmitted packet. The only potential downside is that applications on the remote end may see multiple SIGURG notifications. However, this would occur anyway with other TCP stacks. More importantly, the outcome of such a duplicate notification is likely to be harmless since the signal itself does not carry any information other than the fact that we're in urgent mode. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/ipv4/tcp_output.c12
1 files changed, 8 insertions, 4 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index dda42f0bd7a..557fe16cbfb 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -663,10 +663,14 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
th->urg_ptr = 0;
/* The urg_mode check is necessary during a below snd_una win probe */
- if (unlikely(tcp_urg_mode(tp) &&
- between(tp->snd_up, tcb->seq + 1, tcb->seq + 0xFFFF))) {
- th->urg_ptr = htons(tp->snd_up - tcb->seq);
- th->urg = 1;
+ if (unlikely(tcp_urg_mode(tp))) {
+ if (between(tp->snd_up, tcb->seq + 1, tcb->seq + 0xFFFF)) {
+ th->urg_ptr = htons(tp->snd_up - tcb->seq);
+ th->urg = 1;
+ } else if (after(tcb->seq + 0xFFFF, tp->snd_nxt)) {
+ th->urg_ptr = 0xFFFF;
+ th->urg = 1;
+ }
}
tcp_options_write((__be32 *)(th + 1), tp, &opts, &md5_hash_location);