netdev - Re: [PATCH net-next 3/8] net: enqueue_to_backlog() change vs not running device

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAL+tcoCOwddRuis=3NYOXv0Qwuw9qaLPHY2OAOPyYamKwBHbQg@mail.gmail.com>
Date: Fri, 29 Mar 2024 11:21:12 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 3/8] net: enqueue_to_backlog() change vs not
 running device

On Fri, Mar 29, 2024 at 1:07 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> If the device attached to the packet given to enqueue_to_backlog()
> is not running, we drop the packet.
>
> But we accidentally increase sd->dropped, giving false signals
> to admins: sd->dropped should be reserved to cpu backlog pressure,
> not to temporary glitches at device dismantles.

It seems that drop action happening is intended in this case (see
commit e9e4dd3267d0c ("net: do not process device backlog during
unregistration")). We can see the strange/unexpected behaviour at
least through simply taking a look at /proc/net/softnet_stat file.

>
> While we are at it, perform the netif_running() test before
> we get the rps lock, and use REASON_DEV_READY
> drop reason instead of NOT_SPECIFIED.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  net/core/dev.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 5d36a634f468ffdeaca598c3dd033fe06d240bd0..af7a34b0a7d6683c6ffb21dd3388ed678473d95e 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4791,12 +4791,13 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
>         unsigned long flags;
>         unsigned int qlen;
>
> -       reason = SKB_DROP_REASON_NOT_SPECIFIED;
> +       reason = SKB_DROP_REASON_DEV_READY;
> +       if (!netif_running(skb->dev))
> +               goto bad_dev;
> +
>         sd = &per_cpu(softnet_data, cpu);
>
>         backlog_lock_irq_save(sd, &flags);
> -       if (!netif_running(skb->dev))
> -               goto drop;
>         qlen = skb_queue_len(&sd->input_pkt_queue);
>         if (qlen <= READ_ONCE(net_hotdata.max_backlog) &&
>             !skb_flow_limit(skb, qlen)) {
> @@ -4817,10 +4818,10 @@ static int enqueue_to_backlog(struct sk_buff *skb, int cpu,
>         }
>         reason = SKB_DROP_REASON_CPU_BACKLOG;
>
> -drop:
>         sd->dropped++;
>         backlog_unlock_irq_restore(sd, &flags);
>
> +bad_dev:
>         dev_core_stats_rx_dropped_inc(skb->dev);
>         kfree_skb_reason(skb, reason);
>         return NET_RX_DROP;
> --
> 2.44.0.478.gd926399ef9-goog
>
>