Re: [PATCH net v1] pfcp: fix socket lifetime on netdevice registration failure

[Simon Horman]

On Fri, Sep 18, 2026 at 08:31:58PM +0800, Xuanqiang Luo wrote:
> From: Xuanqiang Luo <luoxuanqiang@xxxxxxxxxx>
> 
> 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
>    ...
> 
> Create the socket in pfcp_dev_init() after initializing the GRO cells,
> and let pfcp_dev_uninit() release it on registration failure or removal.
> 
> Move the RCU wait into pfcp_dev_uninit(), using synchronize_net() after
> socket release to drain receive callbacks before destroying the GRO cells.
> 
> Fixes: 76c8764ef36a5 ("pfcp: add PFCP module")
> Signed-off-by: Xuanqiang Luo <luoxuanqiang@xxxxxxxxxx>
> ---
> A NULL check would fix the crash. Moving socket creation into ndo_init
> also removes the duplicate cleanup and ensures the receive state is
> initialized before enabling the socket's receive callback.

Assuming the NULL check is significantly simpler than this patch,
and that it resolves the bug, think that we should consider:

1. A patch that minimal NULL check for net
2. Follow-up with the approach taken by this patch in net-next

I say this because this seems to be lower risk than skipping to applying
2 to net.

Also, please consider CCing stable on bug fixes.

Link: https://docs.kernel.org/process/maintainer-netdev.html#stable-tree