net/core: check length before updating Ethertype in skb_mpls_{push,pop}

Openvswitch allows to drop a packet's Ethernet header, therefore skb_mpls_push() and skb_mpls_pop() might be called with ethernet=true and mac_len=0. In that case the pointer passed to skb_mod_eth_type() doesn't point to an Ethernet header and the new Ethertype is written at unexpected locations. Fix this by verifying that mac_len is big enough to contain an Ethernet header. Fixes: fa4e0f8 ("net/sched: fix corrupted L2 header with MPLS 'push' and 'pop' actions") Signed-off-by: Guillaume Nault <[email protected]> Acked-by: Davide Caratti <[email protected]> Signed-off-by: David S. Miller <[email protected]>
chewitt · Oct 4, 2020 · 4296adc · 4296adc
1 parent f4544e5
commit 4296adc
Showing 1 changed file with 2 additions and 2 deletions.
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
@@ -5622,7 +5622,7 @@ int skb_mpls_push(struct sk_buff *skb, __be32 mpls_lse, __be16 mpls_proto,
 	lse->label_stack_entry = mpls_lse;
 	skb_postpush_rcsum(skb, lse, MPLS_HLEN);
 
-	if (ethernet)
+	if (ethernet && mac_len >= ETH_HLEN)
 		skb_mod_eth_type(skb, eth_hdr(skb), mpls_proto);
 	skb->protocol = mpls_proto;
 
@@ -5662,7 +5662,7 @@ int skb_mpls_pop(struct sk_buff *skb, __be16 next_proto, int mac_len,
 	skb_reset_mac_header(skb);
 	skb_set_network_header(skb, mac_len);
 
-	if (ethernet) {
+	if (ethernet && mac_len >= ETH_HLEN) {
 		struct ethhdr *hdr;
 
 		/* use mpls_hdr() to get ethertype to account for VLANs. */