From: Hou Tao <houtao1@xxxxxxxxxx> The following slab-use-after-free problem was reported by syzbot: ================================================================== BUG: KASAN: slab-use-after-free in lockdep_register_key+0x253/0x3f0 kernel/locking/lockdep.c:1225 Read of size 8 at addr ffff88805fe2c298 by task syz-executor.1/5906 CPU: 1 PID: 5906 Comm: syz-executor.1 Not tainted 6.9.0-rc5-syzkaller-01473-g2506f6229bd0 #0 ...... Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114 print_address_description mm/kasan/report.c:377 [inline] print_report+0x169/0x550 mm/kasan/report.c:488 kasan_report+0x143/0x180 mm/kasan/report.c:601 lockdep_register_key+0x253/0x3f0 kernel/locking/lockdep.c:1225 htab_map_alloc+0x9b/0xe60 kernel/bpf/hashtab.c:506 map_create+0x90c/0x1200 kernel/bpf/syscall.c:1333 __sys_bpf+0x6d1/0x810 kernel/bpf/syscall.c:5659 do_syscall_x64 arch/x86/entry/common.c:52 [inline] ...... </TASK> Allocated by task 5593: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 poison_kmalloc_redzone mm/kasan/common.c:370 [inline] __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:387 kasan_kmalloc include/linux/kasan.h:211 [inline] __do_kmalloc_node mm/slub.c:3966 [inline] __kmalloc_node_track_caller+0x24e/0x4e0 mm/slub.c:3986 kmalloc_reserve+0x111/0x2a0 net/core/skbuff.c:597 __alloc_skb+0x1f3/0x440 net/core/skbuff.c:666 alloc_skb include/linux/skbuff.h:1308 [inline] alloc_skb_with_frags+0xc3/0x770 net/core/skbuff.c:6455 ...... Freed by task 5593: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3f/0x80 mm/kasan/common.c:68 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:579 poison_slab_object+0xa6/0xe0 mm/kasan/common.c:240 __kasan_slab_free+0x37/0x60 mm/kasan/common.c:256 kasan_slab_free include/linux/kasan.h:184 [inline] slab_free_hook mm/slub.c:2106 [inline] slab_free mm/slub.c:4280 [inline] kfree+0x153/0x3a0 mm/slub.c:4390 skb_kfree_head net/core/skbuff.c:1033 [inline] skb_free_head net/core/skbuff.c:1045 [inline] ...... The buggy address belongs to the object at ffff88805fe2c000 which belongs to the cache kmalloc-2k of size 2048 The buggy address is located 664 bytes inside of freed 2048-byte region [ffff88805fe2c000, ffff88805fe2c800) At first glance, it seems there is a problem with bpf hash-table, because the use-after-free problem is reported when invoking htab_map_alloc(). However, after checking the reported error more carefully, it appears that qdiscs_alloc() is the culprit. The most important clue regarding why qdisc_alloc() is involved is the following: "The buggy address is located 664 bytes inside of freed 2048-byte region". lockdep_register_key() has several callers, and only the offset of lock_class_key in Qdisc in 664. The problem occurs as follow: (1) call qdisc_alloc() After calling lockdep_register_key(), qdisc_alloc() jumps to errout1 label because netdev_alloc_pcpu_stats() or alloc_percpu() fails (e.g., due to mem-cg limitation or SIGKILL). However it doesn't call lockdep_unregister_key() to unregister root_lock_key, but it frees the allocated memory. (2) call htab_map_alloc During the calling of lockdep_register_key(), it finds the lockdep_key registered by free-ed Qdisc and triggers the use-after-free. Fix it by invoking lockdep_unregister_key() in the error path of qdisc_alloc(). Reported-by: syzbot+061f58eec3bde7ee8ffa@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lore.kernel.org/bpf/d28e4f02-965d-96de-ee56-f7a001b67fe7@xxxxxxxxxxxxxxx/T/#m47c0670021ada17869bf887c73438133d879d326 Fixes: af0cb3fa3f9e ("net/sched: fix false lockdep warning on qdisc root lock") Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx> --- net/sched/sch_generic.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 31dfd6c7405b0..d3f6006b563cc 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -982,6 +982,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue, return sch; errout1: + lockdep_unregister_key(&sch->root_lock_key); kfree(sch); errout: return ERR_PTR(err); -- 2.29.2
