Re: [PATCH net-next] net: dev_addr_lists: don't WARN on GFP_ATOMIC kmalloc failure in netif_rx_mode_run

[Jakub Sitnicki <jakub@cloudflare.com>]

On Tue, May 19, 2026 at 02:55 AM -07, Zijing Yin wrote:
> netif_rx_mode_run() fires netdev_WARN() when netif_addr_lists_snapshot()
> returns non-zero. The only path to a non-zero return is -ENOMEM from
> __hw_addr_create() failing its kmalloc(GFP_ATOMIC) -- syzkaller hits it
> via failslab, and it can also be reached under real memory pressure.
>
> This is the only allocator-failure site in this file that WARNs.
> __hw_addr_create() itself, and every other caller of it in this file
> (__hw_addr_add_ex(), dev_uc_add_excl(), dev_uc_add(), dev_mc_add(), ...)
> just propagate the -ENOMEM silently. GFP_ATOMIC is a may-fail allocator;
> callers are required to handle NULL, so a returned -ENOMEM here is an
> expected runtime condition, not an invariant violation.
>
> The miss is self-healing: any subsequent change to dev->uc / dev->mc
> (every dev_{uc,mc}_{add,del}, IFF_PROMISC flip, etc.) calls
> __dev_set_rx_mode() -> netif_rx_mode_queue(), which re-queues the device
> and retries the sync. The only cost of a failed attempt is one stale
> rx-mode window until the next update; nothing in the kernel relies on
> this attempt succeeding.
>
> Demote to net_err_ratelimited() so the condition stays observable in
> dmesg without tripping panic_on_warn.
>
> Reproducer (syzkaller .prog format with setup notes): 
> https://pastebin.com/t7AQKx9v
>
> Fixes: 3554b4345d85 ("net: introduce ndo_set_rx_mode_async and netdev_rx_mode_work")
> Signed-off-by: Zijing Yin <yzjaurora@gmail.com>
> ---
>  net/core/dev_addr_lists.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/dev_addr_lists.c b/net/core/dev_addr_lists.c
> index d73fcb0c6..c6fdcac74 100644
> --- a/net/core/dev_addr_lists.c
> +++ b/net/core/dev_addr_lists.c
> @@ -1275,7 +1275,8 @@ static void netif_rx_mode_run(struct net_device *dev)
>  		err = netif_addr_lists_snapshot(dev, &uc_snap, &mc_snap,
>  						&uc_ref, &mc_ref);
>  		if (err) {
> -			netdev_WARN(dev, "failed to sync uc/mc addresses\n");
> +			net_err_ratelimited("%s: failed to sync uc/mc addresses\n",
> +					    netdev_name(dev));
>  			netif_addr_unlock_bh(dev);
>  			return;
>  		}

1) I'd go with net_warn_ratelimited() instead. The promoted message
level in syslog might cause operational pain, and as you say the
condition is self-healing. Seems unwarranted.

2) Since it has a Fixes tag, should probably be sumitted for 'net' tree.

3) Was this reported by syzbot? If so, there should also be Reported-by
and Closes tags.