net: test tailroom before appending to linear skb

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>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 83c73ba..d54abc0 100644 (file)
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1045,7 +1045,8 @@ 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;

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 2e891d2..7b6d168 100644 (file)
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1503,7 +1503,8 @@ 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;