1. 漏洞描述

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

net/sched: fix lockdep splat in qdisc_tree_reduce_backlog()

qdisc_tree_reduce_backlog() is called with the qdisc lock held,
not RTNL.

We must use qdisc_lookup_rcu() instead of qdisc_lookup()

syzbot reported:

WARNING: suspicious RCU usage
6.1.74-syzkaller #0 Not tainted
-----------------------------
net/sched/sch_api.c:305 suspicious rcu_dereference_protected() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
3 locks held by udevd/1142:
#0: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:306 [inline]
#0: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:747 [inline]
#0: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: net_tx_action+0x64a/0x970 net/core/dev.c:5282
#1: ffff888171861108 (&sch->q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:350 [inline]
#1: ffff888171861108 (&sch->q.lock){+.-.}-{2:2}, at: net_tx_action+0x754/0x970 net/core/dev.c:5297
#2: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:306 [inline]
#2: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:747 [inline]
#2: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: qdisc_tree_reduce_backlog+0x84/0x580 net/sched/sch_api.c:792

stack backtrace:
CPU: 1 PID: 1142 Comm: udevd Not tainted 6.1.74-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Call Trace:
<TASK&gt;
[<ffffffff85b85f14&gt;] __dump_stack lib/dump_stack.c:88 [inline]
[<ffffffff85b85f14&gt;] dump_stack_lvl+0x1b1/0x28f lib/dump_stack.c:106
[<ffffffff85b86007&gt;] dump_stack+0x15/0x1e lib/dump_stack.c:113
[<ffffffff81802299&gt;] lockdep_rcu_suspicious+0x1b9/0x260 kernel/locking/lockdep.c:6592
[<ffffffff84f0054c&gt;] qdisc_lookup+0xac/0x6f0 net/sched/sch_api.c:305
[<ffffffff84f037c3&gt;] qdisc_tree_reduce_backlog+0x243/0x580 net/sched/sch_api.c:811
[<ffffffff84f5b78c&gt;] pfifo_tail_enqueue+0x32c/0x4b0 net/sched/sch_fifo.c:51
[<ffffffff84fbcf63&gt;] qdisc_enqueue include/net/sch_generic.h:833 [inline]
[<ffffffff84fbcf63&gt;] netem_dequeue+0xeb3/0x15d0 net/sched/sch_netem.c:723
[<ffffffff84eecab9&gt;] dequeue_skb net/sched/sch_generic.c:292 [inline]
[<ffffffff84eecab9&gt;] qdisc_restart net/sched/sch_generic.c:397 [inline]
[<ffffffff84eecab9&gt;] __qdisc_run+0x249/0x1e60 net/sched/sch_generic.c:415
[<ffffffff84d7aa96&gt;] qdisc_run+0xd6/0x260 include/net/pkt_sched.h:125
[<ffffffff84d85d29&gt;] net_tx_action+0x7c9/0x970 net/core/dev.c:5313
[<ffffffff85e002bd&gt;] __do_softirq+0x2bd/0x9bd kernel/softirq.c:616
[<ffffffff81568bca&gt;] invoke_softirq kernel/softirq.c:447 [inline]
[<ffffffff81568bca&gt;] __irq_exit_rcu+0xca/0x230 kernel/softirq.c:700
[<ffffffff81568ae9&gt;] irq_exit_rcu+0x9/0x20 kernel/softirq.c:712
[<ffffffff85b89f52&gt;] sysvec_apic_timer_interrupt+0x42/0x90 arch/x86/kernel/apic/apic.c:1107
[<ffffffff85c00ccb&gt;] asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:656

2. 影响范围

3. 影响组件

4. 修复版本

5. 修复方法

6. 下载链接