[PATCH net] net: avoid nul-deref trying to bind mp to incapable device

[PATCH net] net: avoid nul-deref trying to bind mp to incapable device

[Jakub Kicinski]

Sashiko points out that we use qops in __net_mp_open_rxq()
but never validate they are null. This was introduced when
check was moved from netdev_rx_queue_restart().

Look at ops directly instead of the locking config.
qops imply netdev_need_ops_lock(). We used netdev_need_ops_lock()
initially to signify that the real_num_rx_queues check below
is safe without rtnl_lock, but I'm not sure if this is actually
clear to most people, anyway.

Fixes: da7772a2b4ad ("net: move mp->rx_page_size validation to __net_mp_open_rxq()")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: sdf@fomichev.me
CC: almasrymina@google.com
CC: daniel@iogearbox.net
---
 net/core/netdev_rx_queue.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/netdev_rx_queue.c b/net/core/netdev_rx_queue.c
index 668a90658f25..05fd2875d725 100644
--- a/net/core/netdev_rx_queue.c
+++ b/net/core/netdev_rx_queue.c
@@ -117,7 +117,7 @@ int __net_mp_open_rxq(struct net_device *dev, unsigned int rxq_idx,
 	struct netdev_rx_queue *rxq;
 	int ret;
 
-	if (!netdev_need_ops_lock(dev))
+	if (!qops)
 		return -EOPNOTSUPP;
 
 	if (rxq_idx >= dev->real_num_rx_queues) {
-- 
2.53.0

Re: [PATCH net] net: avoid nul-deref trying to bind mp to incapable device

[Daniel Borkmann]

On 4/4/26 2:19 AM, Jakub Kicinski wrote:
> Sashiko points out that we use qops in __net_mp_open_rxq()
> but never validate they are null. This was introduced when
> check was moved from netdev_rx_queue_restart().
> 
> Look at ops directly instead of the locking config.
> qops imply netdev_need_ops_lock(). We used netdev_need_ops_lock()
> initially to signify that the real_num_rx_queues check below
> is safe without rtnl_lock, but I'm not sure if this is actually
> clear to most people, anyway.
> 
> Fixes: da7772a2b4ad ("net: move mp->rx_page_size validation to __net_mp_open_rxq()")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>

Re: [PATCH net] net: avoid nul-deref trying to bind mp to incapable device

[Mina Almasry]

On Fri, Apr 3, 2026 at 5:19 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> Sashiko points out that we use qops in __net_mp_open_rxq()
> but never validate they are null. This was introduced when
> check was moved from netdev_rx_queue_restart().
>
> Look at ops directly instead of the locking config.
> qops imply netdev_need_ops_lock(). We used netdev_need_ops_lock()
> initially to signify that the real_num_rx_queues check below
> is safe without rtnl_lock, but I'm not sure if this is actually
> clear to most people, anyway.
>
> Fixes: da7772a2b4ad ("net: move mp->rx_page_size validation to __net_mp_open_rxq()")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Reviewed-by: Mina Almasry <almasrymina@google.com>

Honestly better for readability too. I was confused why we check that
we need a lock here but never netdev_lock_ops AFAICT.

FWIW I'm not sure why this branch doesn't have NL_SET_ERR_MSG, but I
didn't look deeply. Probably doesn't matter.

Re: [PATCH net] net: avoid nul-deref trying to bind mp to incapable device

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Fri,  3 Apr 2026 17:19:38 -0700 you wrote:
> Sashiko points out that we use qops in __net_mp_open_rxq()
> but never validate they are null. This was introduced when
> check was moved from netdev_rx_queue_restart().
> 
> Look at ops directly instead of the locking config.
> qops imply netdev_need_ops_lock(). We used netdev_need_ops_lock()
> initially to signify that the real_num_rx_queues check below
> is safe without rtnl_lock, but I'm not sure if this is actually
> clear to most people, anyway.
> 
> [...]

Here is the summary with links:
  - [net] net: avoid nul-deref trying to bind mp to incapable device
    https://git.kernel.org/netdev/net/c/944b3b734cfb

You are awesome, thank you!
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