net: skbuff: ensure LSE is pullable before decrementing the MPLS ttl

skb_mpls_dec_ttl() reads the LSE without ensuring that it is contained in the skb "linear" area. Fix this calling pskb_may_pull() before reading the current ttl. Found by code inspection. Fixes: 2a2ea50 ("net: sched: add mpls manipulation actions to TC") Reported-by: Marcelo Ricardo Leitner <[email protected]> Signed-off-by: Davide Caratti <[email protected]> Link: https://lore.kernel.org/r/53659f28be8bc336c113b5254dc637cc76bbae91.1606987074.git.dcaratti@redhat.com Signed-off-by: Jakub Kicinski <[email protected]>
zandrey · Dec 3, 2020 · 13de4ed · 13de4ed
1 parent 6392b5b
commit 13de4ed
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
@@ -5786,6 +5786,9 @@ int skb_mpls_dec_ttl(struct sk_buff *skb)
 	if (unlikely(!eth_p_mpls(skb->protocol)))
 		return -EINVAL;
 
+	if (!pskb_may_pull(skb, skb_network_offset(skb) + MPLS_HLEN))
+		return -ENOMEM;
+
 	lse = be32_to_cpu(mpls_hdr(skb)->label_stack_entry);
 	ttl = (lse & MPLS_LS_TTL_MASK) >> MPLS_LS_TTL_SHIFT;
 	if (!--ttl)