On Thu, Jul 27, 2023 at 08:41:49PM +0000, Shaoying Xu wrote:
> [ Upstream commit 3e337087c3b5805fe0b8a46ba622a962880b5d64 ]
>
> Lion says:
> -------
> In the QFQ scheduler a similar issue to CVE-2023-31436
> persists.
>
> Consider the following code in net/sched/sch_qfq.c:
>
> static int qfq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> struct sk_buff **to_free)
> {
> unsigned int len = qdisc_pkt_len(skb), gso_segs;
>
> // ...
>
> if (unlikely(cl->agg->lmax < len)) {
> pr_debug("qfq: increasing maxpkt from %u to %u for class %u",
> cl->agg->lmax, len, cl->common.classid);
> err = qfq_change_agg(sch, cl, cl->agg->class_weight, len);
> if (err) {
> cl->qstats.drops++;
> return qdisc_drop(skb, sch, to_free);
> }
>
> // ...
>
> }
>
> Similarly to CVE-2023-31436, "lmax" is increased without any bounds
> checks according to the packet length "len". Usually this would not
> impose a problem because packet sizes are naturally limited.
>
> This is however not the actual packet length, rather the
> "qdisc_pkt_len(skb)" which might apply size transformations according to
> "struct qdisc_size_table" as created by "qdisc_get_stab()" in
> net/sched/sch_api.c if the TCA_STAB option was set when modifying the qdisc.
>
> A user may choose virtually any size using such a table.
>
> As a result the same issue as in CVE-2023-31436 can occur, allowing heap
> out-of-bounds read / writes in the kmalloc-8192 cache.
> -------
>
> We can create the issue with the following commands:
>
> tc qdisc add dev $DEV root handle 1: stab mtu 2048 tsize 512 mpu 0 \
> overhead 999999999 linklayer ethernet qfq
> tc class add dev $DEV parent 1: classid 1:1 htb rate 6mbit burst 15k
> tc filter add dev $DEV parent 1: matchall classid 1:1
> ping -I $DEV 1.1.1.2
>
> This is caused by incorrectly assuming that qdisc_pkt_len() returns a
> length within the QFQ_MIN_LMAX < len < QFQ_MAX_LMAX.
>
> Fixes: 462dbc9101ac ("pkt_sched: QFQ Plus: fair-queueing service at DRR cost")
> Reported-by: Lion <nnamrec@xxxxxxxxx>
> Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Signed-off-by: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
> Signed-off-by: Pedro Tammela <pctammela@xxxxxxxxxxxx>
> Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
> Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
> [Backport patch for stable kernels 4.14 and 5.4. Since QFQ_MAX_LMAX is not
> defined, replace it with 1UL << QFQ_MTU_SHIFT.]
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.14, 5.4
> Signed-off-by: Shaoying Xu <shaoyi@xxxxxxxxxx>
>
> ---
> net/sched/sch_qfq.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
Now queued up, thanks.
greg k-h
