Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

net/sched: sch_red: Replace direct dequeue call with peek and qdisc_dequeue_peeked

When red qdisc has children (eg qfq qdisc) whose peek() callback is qdisc_peek_dequeued(), we could get a kernel panic. When the parent of such qdiscs (eg illustrated in patch #3 as tbf) wants to retrieve an skb from its child (red in this case), it will do the following: 1a. do a peek() - and when sensing there's an skb the child can offer, then - the child in this case(red) calls its child's (qfq) peek. qfq does the right thing and will return the gso_skb queue packet. Note: if there wasnt a gso_skb entry then qfq will store it there. 1b. invoke a dequeue() on the child (red). And herein lies the problem. - red will call the child's dequeue() which will essentially just try to grab something of qfq's queue.

[ 78.667668][ T363] KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f] [ 78.667927][ T363] CPU: 1 UID: 0 PID: 363 Comm: ping Not tainted 7.1.0-rc1-00033-g46f74a3f7d57-dirty #790 PREEMPT(full) [ 78.668263][ T363] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 78.668486][ T363] RIP: 0010:qfq_dequeue+0x446/0xc90 [sch_qfq] [ 78.668718][ T363] Code: 54 c0 e8 dd 90 00 f1 48 c7 c7 e0 03 54 c0 48 89 de e8 ce 90 00 f1 48 8d 7b 48 b8 ff ff 37 00 48 89 fa 48 c1 e0 2a 48 c1 ea 03 <80> 3c 02 00 74 05 e8 ef a1 e1 f1 48 8b 7b 48 48 8d 54 24 58 48 8d [ 78.669…