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Message-ID: <20250318143800.GA688833@kernel.org>
Date: Tue, 18 Mar 2025 14:38:00 +0000
From: Simon Horman <horms@...nel.org>
To: Wang Liang <wangliang74@...wei.com>
Cc: dsahern@...nel.org, davem@...emloft.net, edumazet@...gle.com,
kuba@...nel.org, pabeni@...hat.com, fw@...len.de,
daniel@...earbox.net, yuehaibing@...wei.com,
zhangchangzhong@...wei.com, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: fix NULL pointer dereference in l3mdev_l3_rcv
On Thu, Mar 13, 2025 at 09:27:13AM +0800, Wang Liang wrote:
> When delete l3s ipvlan:
>
> ip link del link eth0 ipvlan1 type ipvlan mode l3s
>
> This may cause a null pointer dereference:
>
> Call trace:
> ip_rcv_finish+0x48/0xd0
> ip_rcv+0x5c/0x100
> __netif_receive_skb_one_core+0x64/0xb0
> __netif_receive_skb+0x20/0x80
> process_backlog+0xb4/0x204
> napi_poll+0xe8/0x294
> net_rx_action+0xd8/0x22c
> __do_softirq+0x12c/0x354
>
> This is because l3mdev_l3_rcv() visit dev->l3mdev_ops after
> ipvlan_l3s_unregister() assign the dev->l3mdev_ops to NULL. The process
> like this:
>
> (CPU1) | (CPU2)
> l3mdev_l3_rcv() |
> check dev->priv_flags: |
> master = skb->dev; |
> |
> | ipvlan_l3s_unregister()
> | set dev->priv_flags
> | dev->l3mdev_ops = NULL;
> |
> visit master->l3mdev_ops |
>
> Add lock for dev->priv_flags and dev->l3mdev_ops is too expensive. Resolve
> this issue by add check for master->l3mdev_ops.
Hi Wang Liang,
It seems to me that checking master->l3mdev_ops like this is racy.
>
> Fixes: c675e06a98a4 ("ipvlan: decouple l3s mode dependencies from other modes")
> Signed-off-by: Wang Liang <wangliang74@...wei.com>
> ---
> include/net/l3mdev.h | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/l3mdev.h b/include/net/l3mdev.h
> index f7fe796e8429..b5af87a35a9f 100644
> --- a/include/net/l3mdev.h
> +++ b/include/net/l3mdev.h
> @@ -165,6 +165,7 @@ static inline
> struct sk_buff *l3mdev_l3_rcv(struct sk_buff *skb, u16 proto)
> {
> struct net_device *master = NULL;
> + const struct l3mdev_ops *l3mdev_ops;
If you end up respinning for some other reason, please rearrange the lines
above in reverse xmas tree order - longest line to shortest.
>
> if (netif_is_l3_slave(skb->dev))
> master = netdev_master_upper_dev_get_rcu(skb->dev);
> @@ -172,8 +173,12 @@ struct sk_buff *l3mdev_l3_rcv(struct sk_buff *skb, u16 proto)
> netif_has_l3_rx_handler(skb->dev))
> master = skb->dev;
>
> - if (master && master->l3mdev_ops->l3mdev_l3_rcv)
> - skb = master->l3mdev_ops->l3mdev_l3_rcv(master, skb, proto);
> + if (!master)
> + return skb;
> +
> + l3mdev_ops = master->l3mdev_ops;
> + if (l3mdev_ops && l3mdev_ops->l3mdev_l3_rcv)
> + skb = l3mdev_ops->l3mdev_l3_rcv(master, skb, proto);
>
> return skb;
> }
> --
> 2.34.1
>
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