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authorNeal Cardwell <ncardwell@google.com>2012-01-28 17:29:46 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-02-03 09:22:21 -0800
commitbcabae7b186ccb1e7f8af0df9752c0f6e6b6d83a (patch)
tree3a976e3b18ecac0f4938d7a2e27bd709c1c4ab43
parente5efde92dd328a16d3bd4a9d6fbae2638e0c8646 (diff)
tcp: fix tcp_trim_head() to adjust segment count with skb MSS
[ Upstream commit 5b35e1e6e9ca651e6b291c96d1106043c9af314a ] This commit fixes tcp_trim_head() to recalculate the number of segments in the skb with the skb's existing MSS, so trimming the head causes the skb segment count to be monotonically non-increasing - it should stay the same or go down, but not increase. Previously tcp_trim_head() used the current MSS of the connection. But if there was a decrease in MSS between original transmission and ACK (e.g. due to PMTUD), this could cause tcp_trim_head() to counter-intuitively increase the segment count when trimming bytes off the head of an skb. This violated assumptions in tcp_tso_acked() that tcp_trim_head() only decreases the packet count, so that packets_acked in tcp_tso_acked() could underflow, leading tcp_clean_rtx_queue() to pass u32 pkts_acked values as large as 0xffffffff to ca_ops->pkts_acked(). As an aside, if tcp_trim_head() had really wanted the skb to reflect the current MSS, it should have called tcp_set_skb_tso_segs() unconditionally, since a decrease in MSS would mean that a single-packet skb should now be sliced into multiple segments. Signed-off-by: Neal Cardwell <ncardwell@google.com> Acked-by: Nandita Dukkipati <nanditad@google.com> Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--net/ipv4/tcp_output.c6
1 files changed, 2 insertions, 4 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 63170e297540..097e0c72b3fd 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1138,11 +1138,9 @@ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
sk_mem_uncharge(sk, len);
sock_set_flag(sk, SOCK_QUEUE_SHRUNK);
- /* Any change of skb->len requires recalculation of tso
- * factor and mss.
- */
+ /* Any change of skb->len requires recalculation of tso factor. */
if (tcp_skb_pcount(skb) > 1)
- tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk));
+ tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));
return 0;
}