Subject: [PATCH 06/34] net: test tailroom before appending to linear skb

From: Willem de Bruijn <[email-masked]>
Date: Thu, 17 May 2018 13:13:29 -0400

[ Upstream commit 113f99c3358564a0647d444c2ae34e8b1abfd5b9 ]

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 <[email-masked]>
Signed-off-by: Willem de Bruijn <[email-masked]>
Reviewed-by: Eric Dumazet <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 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 e8e675be60ec..63d5d66e040a 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1040,7 +1040,8 @@ 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 ffbb81609016..0f2d74885bcb 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1488,7 +1488,8 @@ 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;
-- 
2.14.3