[PATCH net] net: test tailroom before appending to linear skb

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: netdev@vger.kernel.org
Cc: davem@davemloft.net, Willem de Bruijn <willemb@google.com>
Subject: [PATCH net] net: test tailroom before appending to linear skb
Date: Thu, 17 May 2018 11:54:37 -0400	[thread overview]
Message-ID: <20180517155437.120414-1-willemdebruijn.kernel@gmail.com> (raw)

From: Willem de Bruijn <willemb@google.com>

Device features may change during transmission. In particular with
corking, a device may toggle scatter-gather in between allocating
and writing to an skb.

Do not unconditionally assume that !NETIF_F_SG at write time implies
that the same held at alloc time and thus the skb has sufficient
tailroom.

This issue predates git history.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
---
 net/ipv4/ip_output.c  | 3 ++-
 net/ipv6/ip6_output.c | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 83c73bab2c3d..c15204ec2eb0 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1045,7 +1045,8 @@ static int __ip_append_data(struct sock *sk,
 		if (copy > length)
 			copy = length;
 
-		if (!(rt->dst.dev->features&NETIF_F_SG)) {
+		if (!(rt->dst.dev->features&NETIF_F_SG) &&
+		    skb_tailroom(skb) > copy) {
 			unsigned int off;
 
 			off = skb->len;
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 2e891d2c30ef..7b6d1689087b 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1503,7 +1503,8 @@ static int __ip6_append_data(struct sock *sk,
 		if (copy > length)
 			copy = length;
 
-		if (!(rt->dst.dev->features&NETIF_F_SG)) {
+		if (!(rt->dst.dev->features&NETIF_F_SG) &&
+		    skb_tailroom(skb) >= copy) {
 			unsigned int off;
 
 			off = skb->len;
-- 
2.17.0.441.gb46fe60e1d-goog
