From: Avi Weiss <thnkslprpt@gmail.com>
To: netdev@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@kernel.org>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Simon Horman <horms@kernel.org>,
Jason Xing <kerneljasonxing@gmail.com>,
Willem de Bruijn <willemb@google.com>,
Mina Almasry <almasrymina@google.com>,
Josef Bacik <josef@toxicpanda.com>,
Jiayuan Chen <jiayuan.chen@linux.dev>,
John Hurley <john.hurley@netronome.com>,
Cong Wang <xiyou.wangcong@gmail.com>,
linux-kernel@vger.kernel.org, Avi Weiss <thnkslprpt@gmail.com>
Subject: [PATCH net] net: skbuff: reject zero MPLS TTL before decrementing
Date: Sat, 31 Oct 2026 13:41:35 +0200 [thread overview]
Message-ID: <20261031114135.3784868-2-thnkslprpt@gmail.com> (raw)
skb_mpls_dec_ttl() decrements the u8 TTL before checking whether it
expired. An incoming TTL of zero wraps to 255, causing the TC MPLS
dec_ttl action to pass an expired packet instead of dropping it.
Reject a zero TTL before the decrement while preserving the existing
behavior for TTL one and valid TTL values.
Fixes: 2a2ea50870ba ("net: sched: add mpls manipulation actions to TC")
Signed-off-by: Avi Weiss <thnkslprpt@gmail.com>
---
net/core/skbuff.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 48f676411724..9b057cc9cbd3 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -6858,7 +6858,7 @@ int skb_mpls_dec_ttl(struct sk_buff *skb)
lse = be32_to_cpu(mpls_hdr(skb)->label_stack_entry);
ttl = (lse & MPLS_LS_TTL_MASK) >> MPLS_LS_TTL_SHIFT;
- if (!--ttl)
+ if (!ttl || !--ttl)
return -EINVAL;
lse &= ~MPLS_LS_TTL_MASK;
--
2.43.0
next reply other threads:[~2026-10-31 11:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-31 11:41 Avi Weiss [this message]
2026-10-31 11:43 ` netdev-bot+sinfo
2026-10-31 12:48 ` Xia Yan
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