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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: fa4e0f8855 ("net/sched: fix corrupted L2 header with MPLS 'push' and 'pop' actions")
Signed-off-by: Guillaume Nault <gnault@redhat.com>
Acked-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Guillaume Nault 2020-10-02 21:53:08 +02:00 committed by David S. Miller
parent f4544e5361
commit 4296adc3e3
1 changed files with 2 additions and 2 deletions
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4
net/core/skbuff.c
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@ -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. */