Re: [PATCH net v5 2/4] netconsole: read np.dev under target_list_lock in local_mac_show()

[Breno Leitao]

On Mon, Nov 02, 2026 at 07:54:50PM +0000, Gustavo Luiz Duarte wrote:
> local_mac_show() loads nt->np.dev and dereferences it with no lock. It
> can race with the interface going away and netconsole_netdev_event()
> eventually calling netdev_put() and freeing the device before we
> dereference it, leading to a UAF.
> 
> The window is only a few instructions wide, so I could only reproduce it
> with an artificially widened window between the load and the
> dereference:
> 
>   BUG: KASAN: slab-use-after-free in local_mac_show+0x4e/0x80
>   Read of size 8 at addr ffff88800e990458 by task uaf/130
>    local_mac_show+0x4e/0x80
>    configfs_read_iter+0x187/0x260
>    vfs_read+0x453/0x5a0
> 
>   Allocated by task 116:
>    alloc_netdev_mqs+0x78/0x830
>    rtnl_create_link+0x53b/0x5c0
> 
>   Freed by task 121:
>    kfree+0x159/0x420
>    device_release+0x77/0x120
>    kobject_put+0xb5/0x160
>    netdev_run_todo+0x420/0x850
>    rtnl_dellink+0x259/0x5b0
> 
> Two places can free np.dev: (1) netconsole_netdev_event() moves a target
> out of STATE_ENABLED under target_list_lock before netdev_put(), and (2)
> process_resume_target() releases np.dev under dynamic_netconsole_mutex.
> 
> Fixes: 0953864160bd ("[NETPOLL]: no need to store local_mac")
> Signed-off-by: Gustavo Luiz Duarte <gustavold@xxxxxxxxx>

Reviewed-by: Breno Leitao <leitao@xxxxxxxxxx>