netdev - [PATCH net] net: skbuff: ensure LSE is pullable before decrementing the MPLS ttl

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Message-Id: <53659f28be8bc336c113b5254dc637cc76bbae91.1606987074.git.dcaratti@redhat.com>
Date:   Thu,  3 Dec 2020 10:58:21 +0100
From:   Davide Caratti <dcaratti@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Cc:     gnault@...hat.com, marcelo.leitner@...il.com,
        Simon Horman <simon.horman@...ronome.com>
Subject: [PATCH net] 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: 2a2ea50870ba ("net: sched: add mpls manipulation actions to TC")
Reported-by: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Signed-off-by: Davide Caratti <dcaratti@...hat.com>
---
 net/core/skbuff.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 06c526e0d810..e578544b2cc7 100644
--- 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)
-- 
2.28.0