3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Neal Cardwell [ 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 Acked-by: Nandita Dukkipati Acked-by: Ilpo Järvinen Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_output.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -1134,11 +1134,9 @@ int tcp_trim_head(struct sock *sk, struc 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; }