Re: [PATCH net v3 1/1] net: l3mdev: Reject non-L3 uppers in slave helpers

[Ido Schimmel <idosch@nvidia.com>]

On Mon, Apr 20, 2026 at 02:32:08PM +0300, Ido Schimmel wrote:
> On Sun, Apr 19, 2026 at 10:53:32PM +0800, Ren Wei wrote:
> > From: Haoze Xie <royenheart@gmail.com>
> > 
> > Several l3mdev slave-side helpers resolve an upper device and then use
> > l3mdev_ops without first proving that the resolved device is still a
> > valid L3 master.
> > 
> > During slave transition, an RCU reader can transiently observe an upper
> > that is not an L3 master. Guard the affected slave-resolved paths by
> > requiring the resolved upper to still be an L3 master before using
> > l3mdev_ops, while keeping existing L3 RX handler providers intact.
> > 
> > Fixes: fdeea7be88b1 ("net: vrf: Set slave's private flag before linking")
> > Cc: stable@kernel.org
> > Reported-by: Yifan Wu <yifanwucs@gmail.com>
> > Reported-by: Juefei Pu <tomapufckgml@gmail.com>
> > Co-developed-by: Yuan Tan <yuantan098@gmail.com>
> > Signed-off-by: Yuan Tan <yuantan098@gmail.com>
> > Suggested-by: Xin Liu <bird@lzu.edu.cn>
> > Tested-by: Haoze Xie <royenheart@gmail.com>
> > Signed-off-by: Haoze Xie <royenheart@gmail.com>
> > Signed-off-by: Ao Zhou <n05ec@lzu.edu.cn>
> 
> I think it's fine for net:
> 
> Reviewed-by: Ido Schimmel <idosch@nvidia.com>

Thought about this again. I would like to check another approach
(synchronize_net() after clearing IFF_L3MDEV_SLAVE). Will update
tomorrow.