linux-kernel - Re: [PATCH nf] netfilter: nf_tables: unconditionally flush pending work before notifier

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Message-Id: <20240703103544.2872-1-hdanton@sina.com>
Date: Wed,  3 Jul 2024 18:35:44 +0800
From: Hillf Danton <hdanton@...a.com>
To: Florian Westphal <fw@...len.de>
Cc: netfilter-devel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	syzkaller-bugs@...glegroups.com,
	syzbot+4fd66a69358fc15ae2ad@...kaller.appspotmail.com
Subject: Re: [PATCH nf] netfilter: nf_tables: unconditionally flush pending work before notifier

On Tue,  2 Jul 2024 16:08:14 +0200 Florian Westphal <fw@...len.de>
> syzbot reports:
> 
> KASAN: slab-uaf in nft_ctx_update include/net/netfilter/nf_tables.h:1831
> KASAN: slab-uaf in nft_commit_release net/netfilter/nf_tables_api.c:9530
> KASAN: slab-uaf int nf_tables_trans_destroy_work+0x152b/0x1750 net/netfilter/nf_tables_api.c:9597
> Read of size 2 at addr ffff88802b0051c4 by task kworker/1:1/45
> [..]
> Workqueue: events nf_tables_trans_destroy_work
> Call Trace:
>  nft_ctx_update include/net/netfilter/nf_tables.h:1831 [inline]
>  nft_commit_release net/netfilter/nf_tables_api.c:9530 [inline]
>  nf_tables_trans_destroy_work+0x152b/0x1750 net/netfilter/nf_tables_api.c:9597
> 
> Problem is that the notifier does a conditional flush, but its possible
> that the table-to-be-removed is still referenced by transactions being
> processed by the worker, so we need to flush unconditionally.
> 
Given trans->table goes thru the lifespan of trans, your proposal is a bandaid
if trans outlives table.