ACK/Cmnt: [SRU][N][PATCH 1/1] net: ioam6: fix OOB and missing lock

[Jian Hui Lee]

On Wed, Jun 24, 2026 at 4:33 PM Cengiz Can via kernel-team
<kernel-team at lists.ubuntu.com> wrote:
>
> From: Justin Iurman <justin.iurman at gmail.com>
>
> When trace->type.bit6 is set:
>
>     if (trace->type.bit6) {
>         ...
>         queue = skb_get_tx_queue(dev, skb);
>         qdisc = rcu_dereference(queue->qdisc);
>
> This code can lead to an out-of-bounds access of the dev->_tx[] array
> when is_input is true. In such a case, the packet is on the RX path and
> skb->queue_mapping contains the RX queue index of the ingress device. If
> the ingress device has more RX queues than the egress device (dev) has
> TX queues, skb_get_queue_mapping(skb) will exceed dev->num_tx_queues.
> Add a check to avoid this situation since skb_get_tx_queue() does not
> clamp the index. This issue has also revealed that per queue visibility
> cannot be accurate and will be replaced later as a new feature.
>
> While at it, add missing lock around qdisc_qstats_qlen_backlog(). The
> function __ioam6_fill_trace_data() is called from both softirq and
> process contexts, hence the use of spin_lock_bh() here.
>
> Fixes: b63c5478e9cb ("ipv6: ioam: Support for Queue depth data field")
> Reported-by: Jakub Kicinski <kuba at kernel.org>
> Closes: https://lore.kernel.org/netdev/20260403214418.2233266-2-kuba@kernel.org/
> Signed-off-by: Justin Iurman <justin.iurman at gmail.com>
> Link: https://patch.msgid.link/20260404134137.24553-1-justin.iurman@gmail.com
> Signed-off-by: Jakub Kicinski <kuba at kernel.org>
> (backported from commit b30b1675aa2bcf0491fd3830b051df4e08a7c8ca)
> [bot_kybele: Used skb_dst(skb)->dev instead of upstream's local `dev` var
>  (absent here), and applied only the OOB queue-mapping check since the
>  spin_lock_bh around qdisc_qstats_qlen_backlog already existed in this tree.]
this patch did add spin_lock_bh() and spin_unlock_bh(), so the comment
here is contradictory. other than that:
Acked-by: Jian Hui Lee <jianhui.lee at canonical.com>

> CVE-2026-43083
> Assisted-by: kybele:claude-opus-4.8
> Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
> ---
>  net/ipv6/ioam6.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv6/ioam6.c b/net/ipv6/ioam6.c
> index a1953cf6131b..8db53f4da660 100644
> --- a/net/ipv6/ioam6.c
> +++ b/net/ipv6/ioam6.c
> @@ -737,12 +737,16 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,
>                 struct Qdisc *qdisc;
>                 __u32 qlen, backlog;
>
> -               if (skb_dst(skb)->dev->flags & IFF_LOOPBACK) {
> +               if (skb_dst(skb)->dev->flags & IFF_LOOPBACK ||
> +                   skb_get_queue_mapping(skb) >= skb_dst(skb)->dev->num_tx_queues) {
>                         *(__be32 *)data = cpu_to_be32(IOAM6_U32_UNAVAILABLE);
>                 } else {
>                         queue = skb_get_tx_queue(skb_dst(skb)->dev, skb);
>                         qdisc = rcu_dereference(queue->qdisc);
> +
> +                       spin_lock_bh(qdisc_lock(qdisc));
>                         qdisc_qstats_qlen_backlog(qdisc, &qlen, &backlog);
> +                       spin_unlock_bh(qdisc_lock(qdisc));
>
>                         *(__be32 *)data = cpu_to_be32(backlog);
>                 }
> --
> 2.43.0
>
>
> --
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