CVE-2024-35892

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> net/sched: fix lockdep splat in qdisc_tree_reduce_backlog()<br /> <br /> qdisc_tree_reduce_backlog() is called with the qdisc lock held,<br /> not RTNL.<br /> <br /> We must use qdisc_lookup_rcu() instead of qdisc_lookup()<br /> <br /> syzbot reported:<br /> <br /> WARNING: suspicious RCU usage<br /> 6.1.74-syzkaller #0 Not tainted<br /> -----------------------------<br /> net/sched/sch_api.c:305 suspicious rcu_dereference_protected() usage!<br /> <br /> other info that might help us debug this:<br /> <br /> rcu_scheduler_active = 2, debug_locks = 1<br /> 3 locks held by udevd/1142:<br /> #0: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:306 [inline]<br /> #0: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:747 [inline]<br /> #0: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: net_tx_action+0x64a/0x970 net/core/dev.c:5282<br /> #1: ffff888171861108 (&amp;sch-&gt;q.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:350 [inline]<br /> #1: ffff888171861108 (&amp;sch-&gt;q.lock){+.-.}-{2:2}, at: net_tx_action+0x754/0x970 net/core/dev.c:5297<br /> #2: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:306 [inline]<br /> #2: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:747 [inline]<br /> #2: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: qdisc_tree_reduce_backlog+0x84/0x580 net/sched/sch_api.c:792<br /> <br /> stack backtrace:<br /> CPU: 1 PID: 1142 Comm: udevd Not tainted 6.1.74-syzkaller #0<br /> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024<br /> Call Trace:<br /> <br /> [] __dump_stack lib/dump_stack.c:88 [inline]<br /> [] dump_stack_lvl+0x1b1/0x28f lib/dump_stack.c:106<br /> [] dump_stack+0x15/0x1e lib/dump_stack.c:113<br /> [] lockdep_rcu_suspicious+0x1b9/0x260 kernel/locking/lockdep.c:6592<br /> [] qdisc_lookup+0xac/0x6f0 net/sched/sch_api.c:305<br /> [] qdisc_tree_reduce_backlog+0x243/0x580 net/sched/sch_api.c:811<br /> [] pfifo_tail_enqueue+0x32c/0x4b0 net/sched/sch_fifo.c:51<br /> [] qdisc_enqueue include/net/sch_generic.h:833 [inline]<br /> [] netem_dequeue+0xeb3/0x15d0 net/sched/sch_netem.c:723<br /> [] dequeue_skb net/sched/sch_generic.c:292 [inline]<br /> [] qdisc_restart net/sched/sch_generic.c:397 [inline]<br /> [] __qdisc_run+0x249/0x1e60 net/sched/sch_generic.c:415<br /> [] qdisc_run+0xd6/0x260 include/net/pkt_sched.h:125<br /> [] net_tx_action+0x7c9/0x970 net/core/dev.c:5313<br /> [] __do_softirq+0x2bd/0x9bd kernel/softirq.c:616<br /> [] invoke_softirq kernel/softirq.c:447 [inline]<br /> [] __irq_exit_rcu+0xca/0x230 kernel/softirq.c:700<br /> [] irq_exit_rcu+0x9/0x20 kernel/softirq.c:712<br /> [] sysvec_apic_timer_interrupt+0x42/0x90 arch/x86/kernel/apic/apic.c:1107<br /> [] asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:656