Re: [PATCH net 1/2] macsec: set IFF_UNICAST_FLT priv flag

[Simon Horman <horms@kernel.org>]

On Mon, Jul 21, 2025 at 09:54:22AM -0700, Stanislav Fomichev wrote:
> Cosmin reports the following locking issue:
> 
>   # BUG: sleeping function called from invalid context at
>   kernel/locking/mutex.c:275
>   #   dump_stack_lvl+0x4f/0x60
>   #   __might_resched+0xeb/0x140
>   #   mutex_lock+0x1a/0x40
>   #   dev_set_promiscuity+0x26/0x90
>   #   __dev_set_promiscuity+0x85/0x170
>   #   __dev_set_rx_mode+0x69/0xa0
>   #   dev_uc_add+0x6d/0x80
>   #   vlan_dev_open+0x5f/0x120 [8021q]
>   #  __dev_open+0x10c/0x2a0
>   #  __dev_change_flags+0x1a4/0x210
>   #  netif_change_flags+0x22/0x60
>   #  do_setlink.isra.0+0xdb0/0x10f0
>   #  rtnl_newlink+0x797/0xb00
>   #  rtnetlink_rcv_msg+0x1cb/0x3f0
>   #  netlink_rcv_skb+0x53/0x100
>   #  netlink_unicast+0x273/0x3b0
>   #  netlink_sendmsg+0x1f2/0x430
> 
> Which is similar to recent syzkaller reports in [0] and [1] and triggers
> because macsec does not advertise IFF_UNICAST_FLT although it has proper
> ndo_set_rx_mode callback that takes care of pushing uc/mc addresses
> down to the real device.
> 
> In general, dev_uc_add call path is problematic for stacking
> non-IFF_UNICAST_FLT because we might grab netdev instance lock under
> addr_list_lock spinlock, so this is not a systemic fix.
> 
> 0: https://lore.kernel.org/netdev/686d55b4.050a0220.1ffab7.0014.GAE@google.com
> 1: https://lore.kernel.org/netdev/68712acf.a00a0220.26a83e.0051.GAE@google.com/
> Link: 2aff4342b0f5b1539c02ffd8df4c7e58dd9746e7.camel@nvidia.com

I think that Link: should be followed by a URL

Link: https://lore.kernel.org/netdev/2aff4342b0f5b1539c02ffd8df4c7e58dd9746e7.camel@nvidia.com

> Fixes: 7e4d784f5810 ("net: hold netdev instance lock during rtnetlink operations")
> Reported-by: Cosmin Ratiu <cratiu@nvidia.com>
> Tested-by: Cosmin Ratiu <cratiu@nvidia.com>
> Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>

Hi Stan,

I ran the test provided by patch 2/2.
When run with with a debug kernel using VNG.

It reliably passes with patch 1/2 applied. And fails without patch 1/2 applied.
Where fails means the kernel panics along the lines of the stack trace in
the commit message.

Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Simon Horman <horms@kernel.org>

...