Patch "tcp: avoid fragmenting peculiar skbs in SACK" has been added to the 4.11-stable tree

This is a note to let you know that I've just added the patch titled

tcp: avoid fragmenting peculiar skbs in SACK

to the 4.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tcp-avoid-fragmenting-peculiar-skbs-in-sack.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Yuchung Cheng <[email protected]>
Date: Wed, 10 May 2017 17:01:27 -0700
Subject: tcp: avoid fragmenting peculiar skbs in SACK

From: Yuchung Cheng <[email protected]>

[ Upstream commit b451e5d24ba6687c6f0e7319c727a709a1846c06 ]

This patch fixes a bug in splitting an SKB during SACK processing. Specifically if an skb contains multiple packets and is only partially sacked in the higher sequences, tcp_match_sack_to_skb() splits the skb and marks the second fragment as SACKed.

The current code further attempts rounding up the first fragment to MSS boundaries. But it misses a boundary condition when the rounded-up fragment size (pkt_len) is exactly skb size. Spliting such an skb is pointless and causses a kernel warning and aborts the SACK processing. This patch universally checks such over-split before calling tcp_fragment to prevent these unnecessary warnings.

---
 net/ipv4/tcp_input.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

@@ -1174,13 +1174,14 @@ static int tcp_match_skb_to_sack(struct
 		 */
 		if (pkt_len > mss) {
 			unsigned int new_len = (pkt_len / mss) * mss;
-			if (!in_sack && new_len < pkt_len) {
+			if (!in_sack && new_len < pkt_len)
 				new_len += mss;
-				if (new_len >= skb->len)
-					return 0;
-			}
 			pkt_len = new_len;
 		}
+
+		if (pkt_len >= skb->len && !in_sack)
+			return 0;
+
 		err = tcp_fragment(sk, skb, pkt_len, mss, GFP_ATOMIC);
 		if (err < 0)
 			return err;

Patches currently in stable-queue which might be from [email protected] are

queue-4.11/tcp-eliminate-negative-reordering-in-tcp_clean_rtx_queue.patch queue-4.11/tcp-avoid-fragmenting-peculiar-skbs-in-sack.patch