Subject: [PATCH 19/34] sock: fix sg page frag coalescing in sk_alloc_sg

From: Daniel Borkmann <[email-masked]>
Date: Mon, 23 Jul 2018 22:37:54 +0200

[ Upstream commit 144fe2bfd236dc814eae587aea7e2af03dbdd755 ]

Current sg coalescing logic in sk_alloc_sg() (latter is used by tls and
sockmap) is not quite correct in that we do fetch the previous sg entry,
however the subsequent check whether the refilled page frag from the
socket is still the same as from the last entry with prior offset and
length matching the start of the current buffer is comparing always the
first sg list entry instead of the prior one.

Fixes: 3c4d7559159b ("tls: kernel TLS support")
Signed-off-by: Daniel Borkmann <[email-masked]>
Acked-by: Dave Watson <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/core/sock.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index 3b6d02854e57..f82843756534 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2270,9 +2270,9 @@ int sk_alloc_sg(struct sock *sk, int len, struct scatterlist *sg,
 		pfrag->offset += use;
 
 		sge = sg + sg_curr - 1;
-		if (sg_curr > first_coalesce && sg_page(sg) == pfrag->page &&
-		    sg->offset + sg->length == orig_offset) {
-			sg->length += use;
+		if (sg_curr > first_coalesce && sg_page(sge) == pfrag->page &&
+		    sge->offset + sge->length == orig_offset) {
+			sge->length += use;
 		} else {
 			sge = sg + sg_curr;
 			sg_unmark_end(sge);
-- 
2.17.1