From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Eric Dumazet <edumazet@google.com>
Cc: "David S . Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Florian Westphal <fw@strlen.de>,
netdev@vger.kernel.org, netfilter-devel@vger.kernel.org,
coreteam@netfilter.org, eric.dumazet@gmail.com,
syzbot+76d4e3a055aec3b007ec@syzkaller.appspotmail.com
Subject: Re: [PATCH net] netfilter: nf_flow_table: drop existing skb dst before skb_dst_set_noref()
Date: Tue, 4 Aug 2026 12:20:21 +0200 [thread overview]
Message-ID: <anG85QHJ8bjqmuXg@chamomile> (raw)
In-Reply-To: <20260804093328.1831847-1-edumazet@google.com>
On Tue, Aug 04, 2026 at 09:33:28AM +0000, Eric Dumazet wrote:
> Incoming skbs passing through netfilter flowtable offload hooks (or XFRM
> offload path) might already carry a ref-counted dst_entry assigned during
> earlier RX or routing steps.
>
> Calling skb_dst_set_noref() when skb already holds a ref-counted dst
> overwrites skb->_skb_refdst, leaking the previous dst_entry reference
> count and triggering a DEBUG_NET_WARN_ON_ONCE assertion in
> skb_dst_check_unset():
>
> WARNING: at skb_dst_check_unset include/linux/skbuff.h:1170
> WARNING: at skb_dst_set_noref include/linux/skbuff.h:1234
> WARNING: at nf_flow_offload_ip_hook+0xf6c/0x2b60 net/netfilter/nf_flow_table_ip.c:864
>
> Drop any existing dst_entry reference with skb_dst_drop(skb) before
> setting the non-referenced flowtable destination.
>
> Fixes: 2a79fd3908ac ("netfilter: nf_flow_table: attach dst to skbs")
> Reported-by: syzbot+76d4e3a055aec3b007ec@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/6a71b141.9511d2ce.1fc5b9.033b.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>
next prev parent reply other threads:[~2026-08-04 10:20 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-04 9:33 [PATCH net] netfilter: nf_flow_table: drop existing skb dst before skb_dst_set_noref() Eric Dumazet
2026-08-04 10:20 ` Pablo Neira Ayuso [this message]
2026-08-06 0:20 ` patchwork-bot+netdevbpf
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