net: sched: prevent scheduling deactivated qdiscs

TAPRIO can schedule a deactivated qdisc after some_qdisc_is_busy() has
reported it idle.

Commit 47e8dbb6e763 ("net/sched: do not reset queues in graft operations")
made graft deactivation skip queue reset, leaving TAPRIO's timer armed.

A late callback schedules NET_TX softirq work, whose dequeue path can
race the unlocked child-queue reset in taprio_reset(). The same skb can
be queued for deferred freeing by RTNL and dequeued for transmission.
In the reproducer, the TAP reader frees it before __rtnl_unlock() reads
its next pointer. KASAN reports a slab-use-after-free in
__rtnl_unlock+0xa3/0xd0, with a read of size 8 from the freed skb.

Reject deactivated qdiscs in __netif_schedule(). Callers' RCU protection
lets the existing grace period join earlier scheduling calls before the
busy check. Restart nonempty transmit queues on reactivation so suppressed
scheduling does not strand packets.

Fixes: 47e8dbb6e763 ("net/sched: do not reset queues in graft operations")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/netdev/20260805102514.740834-1-david.lee@trailofbits.com/
Assisted-by: Codex:gpt-5.6-sol Codex:gpt-5.5-cyber
Signed-off-by: Kyle Zeng <kylebot@openai.com>
Co-developed-by: David Lee <david.lee@trailofbits.com>
Signed-off-by: David Lee <david.lee@trailofbits.com>
Signed-off-by: Dave Miller <davem@davem-thinkpadp1gen8.ibmlond.csb>

0 files changed, 0 insertions, 0 deletions