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Date: Mon, 28 Sep 2026 10:36:28 +0100
From: Simon Horman <horms@kernel.org>
To: Xuanqiang Luo <xuanqiang.luo@linux.dev>
Cc: netdev@vger.kernel.org, andrew+netdev@lunn.ch, davem@davemloft.net,
	edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
	aleksander.lobakin@intel.com, wojciech.drewek@intel.com,
	marcin.szycik@linux.intel.com, linux-kernel@vger.kernel.org,
	xuanqiang.luo@kylinos.cn, stable@vger.kernel.org,
	Xuanqiang Luo <luoxuanqiang@kylinos.cn>
Subject: Re: [PATCH net v2] pfcp: fix socket lifetime on netdevice
 registration failure
Message-ID: <20260928093628.GM13925@horms.kernel.org>
References: <20260924055252.33488-1-xuanqiang.luo@linux.dev>
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In-Reply-To: <20260924055252.33488-1-xuanqiang.luo@linux.dev>

On Thu, Sep 24, 2026 at 01:52:52PM +0800, Xuanqiang Luo wrote:
> From: Xuanqiang Luo <luoxuanqiang@kylinos.cn>
> 
> pfcp_newlink() creates the UDP socket before register_netdevice().
> If registration fails after pfcp_dev_init() succeeds, the core calls
> pfcp_dev_uninit(), which releases the socket and clears pfcp->sk.
> The newlink error path then releases it again, causing a NULL pointer
> dereference. This was observed with failslab fault injection:
> 
>   FAULT_INJECTION: forcing a failure.
>   kobject: kobject_add_internal failed for pfcp0 (error: -12 parent: net)
>   BUG: KASAN: null-ptr-deref in udp_tunnel_sock_release+0x1c/0x50
>   Read of size 8 at addr 0000000000000120 by task ip/1037
>   Call trace:
>    show_stack+0x18/0x24 (C)
>    dump_stack_lvl+0x78/0x90
>    print_report+0x468/0x5cc
>    kasan_report+0xa4/0xf0
>    __asan_load8+0x7c/0xd0
>    udp_tunnel_sock_release+0x1c/0x50
>    pfcp_newlink+0x128/0x184
>    rtnl_newlink+0x848/0xe44
>    rtnetlink_rcv_msg+0x468/0x514
>    netlink_rcv_skb+0xc0/0x1f0
>    rtnetlink_rcv+0x18/0x24
>    netlink_unicast+0x4b8/0x558
>    netlink_sendmsg+0x2b8/0x584
>    ...
> 
> Return from pfcp_del_sock() if pfcp->sk is NULL.
> 
> Fixes: 76c8764ef36a5 ("pfcp: add PFCP module")
> Cc: stable@vger.kernel.org
> Signed-off-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>
> ---
> Changes:
> v2:
>   - Use a NULL check in pfcp_del_sock() as the minimal fix for net and
>     stable. (Simon Horman.)
> 
> v1: https://lore.kernel.org/all/20260918123158.5631-1-xuanqiang.luo@linux.dev/

Thanks for the update, and the link to v1.

Reviewed-by: Simon Horman <horms@kernel.org>