[PATCH net] ipv4: ip_gre: Handle skb_pull() failure in ipgre_xmit()

[Shigeru Yoshida]

In ipgre_xmit(), skb_pull() may fail even if pskb_inet_may_pull() returns
true. For example, applications can create a malformed packet that causes
this problem with PF_PACKET.

This patch fixes the problem by dropping skb and returning from the
function if skb_pull() fails.

Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
Signed-off-by: Shigeru Yoshida <syoshida@xxxxxxxxxx>
---
 net/ipv4/ip_gre.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 22a26d1d29a0..95efa97cb84b 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -643,7 +643,8 @@ static netdev_tx_t ipgre_xmit(struct sk_buff *skb,
 		/* Pull skb since ip_tunnel_xmit() needs skb->data pointing
 		 * to gre header.
 		 */
-		skb_pull(skb, tunnel->hlen + sizeof(struct iphdr));
+		if (!skb_pull(skb, tunnel->hlen + sizeof(struct iphdr)))
+			goto free_skb;
 		skb_reset_mac_header(skb);
 
 		if (skb->ip_summed == CHECKSUM_PARTIAL &&
-- 
2.41.0