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Message-ID: <20260201141739.GE34749@unreal>
Date: Sun, 1 Feb 2026 16:17:39 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Sabrina Dubroca <sd@...asysnail.net>,
Steffen Klassert <steffen.klassert@...unet.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Simon Horman <horms@...nel.org>, Ilan Tayari <ilant@...lanox.com>,
Guy Shapiro <guysh@...lanox.com>,
Yossi Kuperman <yossiku@...lanox.com>,
Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net v2] xfrm: always flush state and policy upon
NETDEV_UNREGISTER event
On Fri, Jan 30, 2026 at 07:42:47PM +0900, Tetsuo Handa wrote:
> syzbot is reporting that "struct xfrm_state" refcount is leaking.
>
> unregister_netdevice: waiting for netdevsim0 to become free. Usage count = 2
> ref_tracker: netdev@...f888052f24618 has 1/1 users at
> __netdev_tracker_alloc include/linux/netdevice.h:4400 [inline]
> netdev_tracker_alloc include/linux/netdevice.h:4412 [inline]
> xfrm_dev_state_add+0x3a5/0x1080 net/xfrm/xfrm_device.c:316
> xfrm_state_construct net/xfrm/xfrm_user.c:986 [inline]
> xfrm_add_sa+0x34ff/0x5fa0 net/xfrm/xfrm_user.c:1022
> xfrm_user_rcv_msg+0x58e/0xc00 net/xfrm/xfrm_user.c:3507
> netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2550
> xfrm_netlink_rcv+0x71/0x90 net/xfrm/xfrm_user.c:3529
> netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
> netlink_unicast+0x5aa/0x870 net/netlink/af_netlink.c:1344
> netlink_sendmsg+0x8c8/0xdd0 net/netlink/af_netlink.c:1894
> sock_sendmsg_nosec net/socket.c:727 [inline]
> __sock_sendmsg net/socket.c:742 [inline]
> ____sys_sendmsg+0xa5d/0xc30 net/socket.c:2592
> ___sys_sendmsg+0x134/0x1d0 net/socket.c:2646
> __sys_sendmsg+0x16d/0x220 net/socket.c:2678
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> This is because commit d77e38e612a0 ("xfrm: Add an IPsec hardware
> offloading API") implemented xfrm_dev_unregister() as no-op despite
> xfrm_dev_state_add() from xfrm_state_construct() acquires a reference
> to "struct net_device".
> I guess that that commit expected that NETDEV_DOWN event is fired before
> NETDEV_UNREGISTER event fires, and also assumed that xfrm_dev_state_add()
> is called only if (dev->features & NETIF_F_HW_ESP) != 0.
>
> Sabrina Dubroca identified steps to reproduce the same symptoms as below.
>
> echo 0 > /sys/bus/netdevsim/new_device
> dev=$(ls -1 /sys/bus/netdevsim/devices/netdevsim0/net/)
> ip xfrm state add src 192.168.13.1 dst 192.168.13.2 proto esp \
> spi 0x1000 mode tunnel aead 'rfc4106(gcm(aes))' $key 128 \
> offload crypto dev $dev dir out
> ethtool -K $dev esp-hw-offload off
> echo 0 > /sys/bus/netdevsim/del_device
>
> Like these steps indicate, the NETIF_F_HW_ESP bit can be cleared after
> xfrm_dev_state_add() acquired a reference to "struct net_device".
> Also, xfrm_dev_state_add() does not check for the NETIF_F_HW_ESP bit
> when acquiring a reference to "struct net_device".
>
> Commit 03891f820c21 ("xfrm: handle NETDEV_UNREGISTER for xfrm device")
> re-introduced the NETDEV_UNREGISTER event to xfrm_dev_event(), but that
> commit for unknown reason chose to share xfrm_dev_down() between the
> NETDEV_DOWN event and the NETDEV_UNREGISTER event.
> I guess that that commit missed the behavior in the previous paragraph.
>
> Therefore, we need to re-introduce xfrm_dev_unregister() in order to
> release the reference to "struct net_device" by unconditionally flushing
> state and policy.
>
> Reported-by: syzbot+881d65229ca4f9ae8c84@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
> Fixes: d77e38e612a0 ("xfrm: Add an IPsec hardware offloading API")
> Cc: Sabrina Dubroca <sd@...asysnail.net>
> Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> ---
> v2:
> - Don't change xfrm_dev_down(), re-introduce xfrm_dev_unregister() instead.
>
> v1:
> - https://lkml.kernel.org/r/1de734e2-1da6-4b5c-8e03-66af7f88d074@I-love.SAKURA.ne.jp
>
> net/xfrm/xfrm_device.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
I believe this is the correct solution, but I do not feel confident enough to
add my Reviewed-by.
Steffen,
If you decide to take it, please queue it in your -next branch, so we will have enough
time to test in our regression. It seems too risky for -rc8.
Thanks
>
> diff --git a/net/xfrm/xfrm_device.c b/net/xfrm/xfrm_device.c
> index 52ae0e034d29..550457e4c4f0 100644
> --- a/net/xfrm/xfrm_device.c
> +++ b/net/xfrm/xfrm_device.c
> @@ -544,6 +544,14 @@ static int xfrm_dev_down(struct net_device *dev)
> return NOTIFY_DONE;
> }
>
> +static int xfrm_dev_unregister(struct net_device *dev)
> +{
> + xfrm_dev_state_flush(dev_net(dev), dev, true);
> + xfrm_dev_policy_flush(dev_net(dev), dev, true);
> +
> + return NOTIFY_DONE;
> +}
> +
> static int xfrm_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
> {
> struct net_device *dev = netdev_notifier_info_to_dev(ptr);
> @@ -556,8 +564,10 @@ static int xfrm_dev_event(struct notifier_block *this, unsigned long event, void
> return xfrm_api_check(dev);
>
> case NETDEV_DOWN:
> - case NETDEV_UNREGISTER:
> return xfrm_dev_down(dev);
> +
> + case NETDEV_UNREGISTER:
> + return xfrm_dev_unregister(dev);
> }
> return NOTIFY_DONE;
> }
> --
> 2.47.3
>
>
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