[PATCH V2] net: Fix skb_under_panic oops in neigh_resolve_output

[PATCH V2] net: Fix skb_under_panic oops in neigh_resolve_output

[ramesh.nagappa]

The retry loop in neigh_resolve_output() and neigh_connected_output()
call dev_hard_header() with out reseting the skb to network_header.
This causes the retry to fail with skb_under_panic. The fix is to
reset the network_header within the retry loop.

Signed-off-by: Ramesh Nagappa <ramesh.nagappa@ericsson.com>
Reviewed-by: Shawn Lu <shawn.lu@ericsson.com>
Reviewed-by: Robert Coulson <robert.coulson@ericsson.com>
Reviewed-by: Billie Alsup <billie.alsup@ericsson.com>
---
 net/core/neighbour.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 117afaf..058bb1e 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1301,8 +1301,6 @@ int neigh_resolve_output(struct neighbour *neigh, struct sk_buff *skb)
 	if (!dst)
 		goto discard;
 
-	__skb_pull(skb, skb_network_offset(skb));
-
 	if (!neigh_event_send(neigh, skb)) {
 		int err;
 		struct net_device *dev = neigh->dev;
@@ -1312,6 +1310,7 @@ int neigh_resolve_output(struct neighbour *neigh, struct sk_buff *skb)
 			neigh_hh_init(neigh, dst);
 
 		do {
+			__skb_pull(skb, skb_network_offset(skb));
 			seq = read_seqbegin(&neigh->ha_lock);
 			err = dev_hard_header(skb, dev, ntohs(skb->protocol),
 					      neigh->ha, NULL, skb->len);
@@ -1342,9 +1341,8 @@ int neigh_connected_output(struct neighbour *neigh, struct sk_buff *skb)
 	unsigned int seq;
 	int err;
 
-	__skb_pull(skb, skb_network_offset(skb));
-
 	do {
+		__skb_pull(skb, skb_network_offset(skb));
 		seq = read_seqbegin(&neigh->ha_lock);
 		err = dev_hard_header(skb, dev, ntohs(skb->protocol),
 				      neigh->ha, NULL, skb->len);
-- 
1.7.11.4

Re: [PATCH V2] net: Fix skb_under_panic oops in neigh_resolve_output

[David Miller]

From: ramesh.nagappa@gmail.com
Date: Fri,  5 Oct 2012 22:10:15 -0700

> The retry loop in neigh_resolve_output() and neigh_connected_output()
> call dev_hard_header() with out reseting the skb to network_header.
> This causes the retry to fail with skb_under_panic. The fix is to
> reset the network_header within the retry loop.
> 
> Signed-off-by: Ramesh Nagappa <ramesh.nagappa@ericsson.com>
> Reviewed-by: Shawn Lu <shawn.lu@ericsson.com>
> Reviewed-by: Robert Coulson <robert.coulson@ericsson.com>
> Reviewed-by: Billie Alsup <billie.alsup@ericsson.com>

Applied and queued up for -stable, thanks.