{"id":"CVE-2024-35892","summary":"net/sched: fix lockdep splat in qdisc_tree_reduce_backlog()","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: fix lockdep splat in qdisc_tree_reduce_backlog()\n\nqdisc_tree_reduce_backlog() is called with the qdisc lock held,\nnot RTNL.\n\nWe must use qdisc_lookup_rcu() instead of qdisc_lookup()\n\nsyzbot reported:\n\nWARNING: suspicious RCU usage\n6.1.74-syzkaller #0 Not tainted\n-----------------------------\nnet/sched/sch_api.c:305 suspicious rcu_dereference_protected() usage!\n\nother info that might help us debug this:\n\nrcu_scheduler_active = 2, debug_locks = 1\n3 locks held by udevd/1142:\n  #0: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:306 [inline]\n  #0: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:747 [inline]\n  #0: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: net_tx_action+0x64a/0x970 net/core/dev.c:5282\n  #1: ffff888171861108 (&sch-\u003eq.lock){+.-.}-{2:2}, at: spin_lock include/linux/spinlock.h:350 [inline]\n  #1: ffff888171861108 (&sch-\u003eq.lock){+.-.}-{2:2}, at: net_tx_action+0x754/0x970 net/core/dev.c:5297\n  #2: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:306 [inline]\n  #2: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:747 [inline]\n  #2: ffffffff87c729a0 (rcu_read_lock){....}-{1:2}, at: qdisc_tree_reduce_backlog+0x84/0x580 net/sched/sch_api.c:792\n\nstack backtrace:\nCPU: 1 PID: 1142 Comm: udevd Not tainted 6.1.74-syzkaller #0\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024\nCall Trace:\n \u003cTASK\u003e\n  [\u003cffffffff85b85f14\u003e] __dump_stack lib/dump_stack.c:88 [inline]\n  [\u003cffffffff85b85f14\u003e] dump_stack_lvl+0x1b1/0x28f lib/dump_stack.c:106\n  [\u003cffffffff85b86007\u003e] dump_stack+0x15/0x1e lib/dump_stack.c:113\n  [\u003cffffffff81802299\u003e] lockdep_rcu_suspicious+0x1b9/0x260 kernel/locking/lockdep.c:6592\n  [\u003cffffffff84f0054c\u003e] qdisc_lookup+0xac/0x6f0 net/sched/sch_api.c:305\n  [\u003cffffffff84f037c3\u003e] qdisc_tree_reduce_backlog+0x243/0x580 net/sched/sch_api.c:811\n  [\u003cffffffff84f5b78c\u003e] pfifo_tail_enqueue+0x32c/0x4b0 net/sched/sch_fifo.c:51\n  [\u003cffffffff84fbcf63\u003e] qdisc_enqueue include/net/sch_generic.h:833 [inline]\n  [\u003cffffffff84fbcf63\u003e] netem_dequeue+0xeb3/0x15d0 net/sched/sch_netem.c:723\n  [\u003cffffffff84eecab9\u003e] dequeue_skb net/sched/sch_generic.c:292 [inline]\n  [\u003cffffffff84eecab9\u003e] qdisc_restart net/sched/sch_generic.c:397 [inline]\n  [\u003cffffffff84eecab9\u003e] __qdisc_run+0x249/0x1e60 net/sched/sch_generic.c:415\n  [\u003cffffffff84d7aa96\u003e] qdisc_run+0xd6/0x260 include/net/pkt_sched.h:125\n  [\u003cffffffff84d85d29\u003e] net_tx_action+0x7c9/0x970 net/core/dev.c:5313\n  [\u003cffffffff85e002bd\u003e] __do_softirq+0x2bd/0x9bd kernel/softirq.c:616\n  [\u003cffffffff81568bca\u003e] invoke_softirq kernel/softirq.c:447 [inline]\n  [\u003cffffffff81568bca\u003e] __irq_exit_rcu+0xca/0x230 kernel/softirq.c:700\n  [\u003cffffffff81568ae9\u003e] irq_exit_rcu+0x9/0x20 kernel/softirq.c:712\n  [\u003cffffffff85b89f52\u003e] sysvec_apic_timer_interrupt+0x42/0x90 arch/x86/kernel/apic/apic.c:1107\n  [\u003cffffffff85c00ccb\u003e] asm_sysvec_apic_timer_interrupt+0x1b/0x20 arch/x86/include/asm/idtentry.h:656","modified":"2026-04-02T11:52:40.206561Z","published":"2024-05-19T08:34:47.914Z","related":["SUSE-SU-2024:2571-1","SUSE-SU-2024:2896-1","SUSE-SU-2024:2973-1","SUSE-SU-2025:20008-1","SUSE-SU-2025:20028-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/35xxx/CVE-2024-35892.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/07696415526bee0607e495017369c7303a4792e1"},{"type":"WEB","url":"https://git.kernel.org/stable/c/7eb322360b0266481e560d1807ee79e0cef5742b"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b7d1ce2cc7192e8a037faa3f5d3ba72c25976460"},{"type":"WEB","url":"https://git.kernel.org/stable/c/c040b99461a5bfc14c2d0cbb1780fcc3a4706c7e"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/35xxx/CVE-2024-35892.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-35892"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"9d9a38b5639fcefacc1e977567fb4b4e4a74d0b3"},{"fixed":"b7d1ce2cc7192e8a037faa3f5d3ba72c25976460"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"d636fc5dd692c8f4e00ae6e0359c0eceeb5d9bdb"},{"fixed":"c040b99461a5bfc14c2d0cbb1780fcc3a4706c7e"},{"fixed":"07696415526bee0607e495017369c7303a4792e1"},{"fixed":"7eb322360b0266481e560d1807ee79e0cef5742b"}]},{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"0"},{"last_affected":"3a4741bb13caf482b877b10ac1bcf7390cad7077"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2024-35892.json"}}],"schema_version":"1.7.5"}