[TCP]: Check num sacks in SACK fast path

We clear the unused parts of the SACK cache, This prevents us from mistakenly
taking the cache data if the old data in the SACK cache is the same as the data
in the SACK block. This assumes that we never receive an empty SACK block with
start and end both at zero.

Signed-off-by: Baruch Even <baruch@ev-en.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 0 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 870f53afd363..c6109895bb5e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -998,6 +998,11 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
                 tp->recv_sack_cache[i].start_seq = start_seq;
                 tp->recv_sack_cache[i].end_seq = end_seq;
         }
+        /* Clear the rest of the cache sack blocks so they won't match mistakenly. */
+        for (; i < ARRAY_SIZE(tp->recv_sack_cache); i++) {
+                tp->recv_sack_cache[i].start_seq = 0;
+                tp->recv_sack_cache[i].end_seq = 0;
+        }
 
         first_sack_index = 0;
         if (flag)