[PATCH 3.16 331/366] net: test tailroom before appending to linear skb

[Ben Hutchings]

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Willem de Bruijn <willemb@xxxxxxxxxx>

commit 113f99c3358564a0647d444c2ae34e8b1abfd5b9 upstream.

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@xxxxxxxxxx>
Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/ipv4/ip_output.c  | 3 ++-
 net/ipv6/ip6_output.c | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1025,7 +1025,8 @@ alloc_new_skb:
 		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;
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1453,7 +1453,8 @@ alloc_new_skb:
 		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;