linux-kernel - Re: [syzbot] [netfilter?] WARNING in nf_conntrack_cleanup_net

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aT1pyVp3pQRvCjLn@strlen.de>
Date: Sat, 13 Dec 2025 14:27:37 +0100
From: Florian Westphal <fw@...len.de>
To: Jakub Kicinski <kuba@...nel.org>
Cc: syzbot <syzbot+4393c47753b7808dac7d@...kaller.appspotmail.com>,
	coreteam@...filter.org, davem@...emloft.net, edumazet@...gle.com,
	horms@...nel.org, kadlec@...filter.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org, pabeni@...hat.com,
	pablo@...filter.org, phil@....cc, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [netfilter?] WARNING in nf_conntrack_cleanup_net_list

Jakub Kicinski <kuba@...nel.org> wrote:
> On Thu, 11 Dec 2025 10:38:31 -0800 syzbot wrote:
> > ------------[ cut here ]------------
> > conntrack cleanup blocked for 60s
> > WARNING: net/netfilter/nf_conntrack_core.c:2512 at
> 
> Yes, I was about to comment on the patch which added the warning..
> 
> There is still a leak somewhere. Running ip_defrag.sh and then load /
> unload ipvlan repros this (modprobe ipvlan is a quick check if the
> cleanup thread is wedged, if it is modprobe will hang, if it isn't
> run ip_defrag.sh, again etc).
> 
> I looked around last night but couldn't find an skb stuck anywhere.
> The nf_conntrack_net->count was == 1

Its caused skb skb fraglist skbs that still hold nf_conn references
on the softnet data defer lists.

setting net.core.skb_defer_max=0 makes the hang disappear for me.