netdev - [PATCH] net/sched: unregister root_lock_key in the error path of qdisc

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Message-Id: <20240516133035.1050113-1-houtao@huaweicloud.com>
Date: Thu, 16 May 2024 21:30:35 +0800
From: Hou Tao <houtao@...weicloud.com>
To: netdev@...r.kernel.org,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Jiri Pirko <jiri@...nulli.us>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Davide Caratti <dcaratti@...hat.com>
Cc: bpf@...r.kernel.org,
	houtao1@...wei.com
Subject: [PATCH] net/sched: unregister root_lock_key in the error path of qdisc_alloc()

From: Hou Tao <houtao1@...wei.com>

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@...kaller.appspotmail.com
Closes: https://lore.kernel.org/bpf/d28e4f02-965d-96de-ee56-f7a001b67fe7@huaweicloud.com/T/#m47c0670021ada17869bf887c73438133d879d326
Fixes: af0cb3fa3f9e ("net/sched: fix false lockdep warning on qdisc root lock")
Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 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