[PATCH] net_sched: check skb_transport_header_was_set() in qdisc_pkt_len_init()

[Matthew Rosato <mjrosato@linux.vnet.ibm.com>]

commit 1def9238d4aa2 (net_sched: more precise pkt_len computation) does
not check to see if skb_transport_header is valid prior to using it in
qdisc_pkt_len_init(), which can lead to a kernel panic if
skb_transport_header is not valid but gso_size is nonzero.  This patch
adds a check for skb_transport_header_was_set().

I managed to hit this scenario by driving a burst of traffic from a
qemu guest through a macvtap interface, causing a panic in the host kernel.

Signed-off-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
---
 net/core/dev.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index fc1e289..5d0d3af 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2596,7 +2596,7 @@ static void qdisc_pkt_len_init(struct sk_buff *skb)
 	/* To get more precise estimation of bytes sent on wire,
 	 * we add to pkt_len the headers size of all segments
 	 */
-	if (shinfo->gso_size)  {
+	if (shinfo->gso_size && skb_transport_header_was_set(skb))  {
 		unsigned int hdr_len;
 		u16 gso_segs = shinfo->gso_segs;
 
-- 
1.7.9.5