[syzbot] KASAN: use-after-free Read in __usb_hcd_giveback_urb (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ef4d3ea40565 afs: Fix server->active leak in afs_put_server
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=100b244d880000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e7e79f8a1e34200
dashboard link: https://syzkaller.appspot.com/bug?extid=712fd0e60dda3ba34642
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ef790e7777cd/disk-ef4d3ea4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2ed3c6bc9230/vmlinux-ef4d3ea4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f1dbd004fa88/bzImage-ef4d3ea4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+712fd0...@syzkaller.appspotmail.com

xpad 3-1:179.65: xpad_irq_in - usb_submit_urb failed with result -19
xpad 3-1:179.65: xpad_irq_out - usb_submit_urb failed with result -19
==================================================================
BUG: KASAN: use-after-free in register_lock_class+0x8d2/0x9b0 kernel/locking/lockdep.c:1338
Read of size 1 at addr ffff88807a58b091 by task kworker/u4:3/46

CPU: 0 PID: 46 Comm: kworker/u4:3 Not tainted 6.1.0-rc7-syzkaller-00103-gef4d3ea40565 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Workqueue: bat_events batadv_nc_worker
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
print_address_description+0x74/0x340 mm/kasan/report.c:284
print_report+0x107/0x220 mm/kasan/report.c:395
kasan_report+0x139/0x170 mm/kasan/report.c:495
register_lock_class+0x8d2/0x9b0 kernel/locking/lockdep.c:1338
__lock_acquire+0xe4/0x1f60 kernel/locking/lockdep.c:4934
lock_acquire+0x1a7/0x400 kernel/locking/lockdep.c:5668
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0xd1/0x120 kernel/locking/spinlock.c:162
__wake_up_common_lock kernel/sched/wait.c:136 [inline]
__wake_up+0xf8/0x1c0 kernel/sched/wait.c:156
__usb_hcd_giveback_urb+0x3a0/0x530 drivers/usb/core/hcd.c:1674
dummy_timer+0x86b/0x3110 drivers/usb/gadget/udc/dummy_hcd.c:1988
call_timer_fn+0xf5/0x210 kernel/time/timer.c:1474
expire_timers kernel/time/timer.c:1519 [inline]
__run_timers+0x76a/0x980 kernel/time/timer.c:1790
run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1803
__do_softirq+0x277/0x75b kernel/softirq.c:571
__irq_exit_rcu+0xec/0x170 kernel/softirq.c:650
irq_exit_rcu+0x5/0x20 kernel/softirq.c:662
sysvec_apic_timer_interrupt+0x91/0xb0 arch/x86/kernel/apic/apic.c:1107
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:649
RIP: 0010:lock_acquire+0x21e/0x400 kernel/locking/lockdep.c:5672
Code: 23 00 74 08 4c 89 f7 e8 20 aa 75 00 f6 44 24 61 02 0f 85 76 01 00 00 41 f7 c7 00 02 00 00 74 01 fb 48 c7 44 24 40 0e 36 e0 45 <4b> c7 04 2c 00 00 00 00 43 c7 44 2c 09 00 00 00 00 43 c7 44 2c 11
RSP: 0018:ffffc90000b77a60 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 1ffff9200016ef58 RCX: ffff888018f2c4c8
RDX: dffffc0000000000 RSI: ffffffff8b0da2a0 RDI: ffffffff8b68fcc0
RBP: ffffc90000b77bb8 R08: dffffc0000000000 R09: fffffbfff20e4c29
R10: fffffbfff20e4c29 R11: 1ffffffff20e4c28 R12: dffffc0000000000
R13: 1ffff9200016ef54 R14: ffffc90000b77ac0 R15: 0000000000000246
rcu_lock_acquire+0x2a/0x30 include/linux/rcupdate.h:304
rcu_read_lock include/linux/rcupdate.h:738 [inline]
batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:408 [inline]
batadv_nc_worker+0xc8/0x5b0 net/batman-adv/network-coding.c:719
process_one_work+0x81c/0xd10 kernel/workqueue.c:2289
worker_thread+0xb14/0x1330 kernel/workqueue.c:2436
kthread+0x266/0x300 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
</TASK>

Allocated by task 3741:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4c/0x70 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:371 [inline]
__kasan_kmalloc+0x97/0xb0 mm/kasan/common.c:380
kmalloc include/linux/slab.h:553 [inline]
kzalloc include/linux/slab.h:689 [inline]
xpad_probe+0x3de/0x1b70 drivers/input/joystick/xpad.c:1954
usb_probe_interface+0x66e/0xb60 drivers/usb/core/driver.c:396
call_driver_probe+0x96/0x250
really_probe+0x24c/0x9f0 drivers/base/dd.c:639
__driver_probe_device+0x1f4/0x3f0 drivers/base/dd.c:778
driver_probe_device+0x50/0x240 drivers/base/dd.c:808
__device_attach_driver+0x272/0x3c0 drivers/base/dd.c:936
bus_for_each_drv+0x18a/0x210 drivers/base/bus.c:427
__device_attach+0x372/0x5a0 drivers/base/dd.c:1008
bus_probe_device+0xb8/0x1f0 drivers/base/bus.c:487
device_add+0xb20/0xf90 drivers/base/core.c:3517
usb_set_configuration+0x1a5f/0x20e0 drivers/usb/core/message.c:2170
usb_generic_driver_probe+0x83/0x140 drivers/usb/core/generic.c:238
usb_probe_device+0x131/0x260 drivers/usb/core/driver.c:293
call_driver_probe+0x96/0x250
really_probe+0x24c/0x9f0 drivers/base/dd.c:639
__driver_probe_device+0x1f4/0x3f0 drivers/base/dd.c:778
driver_probe_device+0x50/0x240 drivers/base/dd.c:808
__device_attach_driver+0x272/0x3c0 drivers/base/dd.c:936
bus_for_each_drv+0x18a/0x210 drivers/base/bus.c:427
__device_attach+0x372/0x5a0 drivers/base/dd.c:1008
bus_probe_device+0xb8/0x1f0 drivers/base/bus.c:487
device_add+0xb20/0xf90 drivers/base/core.c:3517
usb_new_device+0xbc2/0x18b0 drivers/usb/core/hub.c:2573
hub_port_connect+0x103b/0x2910 drivers/usb/core/hub.c:5353
hub_port_connect_change+0x619/0xbe0 drivers/usb/core/hub.c:5497
port_event+0xec6/0x13b0 drivers/usb/core/hub.c:5653
hub_event+0x5c1/0xd80 drivers/usb/core/hub.c:5735
process_one_work+0x81c/0xd10 kernel/workqueue.c:2289
worker_thread+0xb14/0x1330 kernel/workqueue.c:2436
kthread+0x266/0x300 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306

Freed by task 3709:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4c/0x70 mm/kasan/common.c:52
kasan_save_free_info+0x27/0x40 mm/kasan/generic.c:511
____kasan_slab_free+0xd6/0x120 mm/kasan/common.c:236
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1724 [inline]
slab_free_freelist_hook+0x12e/0x1a0 mm/slub.c:1750
slab_free mm/slub.c:3661 [inline]
__kmem_cache_free+0x71/0x110 mm/slub.c:3674
xpad_disconnect+0x332/0x450 drivers/input/joystick/xpad.c:2135
usb_unbind_interface+0x1f2/0x860 drivers/usb/core/driver.c:458
device_remove drivers/base/dd.c:550 [inline]
__device_release_driver drivers/base/dd.c:1249 [inline]
device_release_driver_internal+0x5bc/0x8a0 drivers/base/dd.c:1275
bus_remove_device+0x2fd/0x410 drivers/base/bus.c:529
device_del+0x6ec/0xbe0 drivers/base/core.c:3704
usb_disable_device+0x3dd/0x820 drivers/usb/core/message.c:1419
usb_disconnect+0x346/0x890 drivers/usb/core/hub.c:2235
hub_port_connect+0x296/0x2910 drivers/usb/core/hub.c:5197
hub_port_connect_change+0x619/0xbe0 drivers/usb/core/hub.c:5497
port_event+0xec6/0x13b0 drivers/usb/core/hub.c:5653
hub_event+0x5c1/0xd80 drivers/usb/core/hub.c:5735
process_one_work+0x81c/0xd10 kernel/workqueue.c:2289
worker_thread+0xb14/0x1330 kernel/workqueue.c:2436
kthread+0x266/0x300 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306

The buggy address belongs to the object at ffff88807a58b000
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 145 bytes inside of
1024-byte region [ffff88807a58b000, ffff88807a58b400)

The buggy address belongs to the physical page:
page:ffffea0001e96200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7a588
head:ffffea0001e96200 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000001 ffff888012841dc0
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 3623, tgid 3621 (syz-fuzzer), ts 88914482150, free_ts 88747836155
prep_new_page mm/page_alloc.c:2539 [inline]
get_page_from_freelist+0x72b/0x7a0 mm/page_alloc.c:4291
__alloc_pages+0x259/0x560 mm/page_alloc.c:5558
alloc_slab_page+0x70/0xf0 mm/slub.c:1794
allocate_slab+0x5e/0x4b0 mm/slub.c:1939
new_slab mm/slub.c:1992 [inline]
___slab_alloc+0x7f4/0xeb0 mm/slub.c:3180
__slab_alloc mm/slub.c:3279 [inline]
slab_alloc_node mm/slub.c:3364 [inline]
__kmem_cache_alloc_node+0x252/0x310 mm/slub.c:3437
__do_kmalloc_node mm/slab_common.c:954 [inline]
__kmalloc_node_track_caller+0x9c/0x190 mm/slab_common.c:975
kmalloc_reserve net/core/skbuff.c:437 [inline]
__alloc_skb+0x11d/0x620 net/core/skbuff.c:509
alloc_skb include/linux/skbuff.h:1267 [inline]
__tcp_send_ack+0x98/0x5f0 net/ipv4/tcp_output.c:3960
tcp_cleanup_rbuf net/ipv4/tcp.c:1628 [inline]
tcp_recvmsg_locked+0x1cf8/0x25f0 net/ipv4/tcp.c:2649
tcp_recvmsg+0x22b/0x8b0 net/ipv4/tcp.c:2679
inet_recvmsg+0x13a/0x250 net/ipv4/af_inet.c:861
sock_recvmsg_nosec net/socket.c:995 [inline]
sock_recvmsg net/socket.c:1013 [inline]
sock_read_iter+0x3fa/0x530 net/socket.c:1086
call_read_iter include/linux/fs.h:2193 [inline]
new_sync_read fs/read_write.c:389 [inline]
vfs_read+0x7cf/0xbc0 fs/read_write.c:470
ksys_read+0x19b/0x2c0 fs/read_write.c:613
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1459 [inline]
free_pcp_prepare+0x80c/0x8f0 mm/page_alloc.c:1509
free_unref_page_prepare mm/page_alloc.c:3387 [inline]
free_unref_page+0x7d/0x630 mm/page_alloc.c:3483
__skb_frag_unref include/linux/skbuff.h:3385 [inline]
skb_release_data+0x37a/0x6d0 net/core/skbuff.c:783
skb_release_all net/core/skbuff.c:854 [inline]
__kfree_skb+0x56/0x1d0 net/core/skbuff.c:868
tcp_eat_recv_skb net/ipv4/tcp.c:1638 [inline]
tcp_recvmsg_locked+0x14b2/0x25f0 net/ipv4/tcp.c:2633
tcp_recvmsg+0x22b/0x8b0 net/ipv4/tcp.c:2679
inet_recvmsg+0x13a/0x250 net/ipv4/af_inet.c:861
sock_recvmsg_nosec net/socket.c:995 [inline]
sock_recvmsg net/socket.c:1013 [inline]
sock_read_iter+0x3fa/0x530 net/socket.c:1086
call_read_iter include/linux/fs.h:2193 [inline]
new_sync_read fs/read_write.c:389 [inline]
vfs_read+0x7cf/0xbc0 fs/read_write.c:470
ksys_read+0x19b/0x2c0 fs/read_write.c:613
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Memory state around the buggy address:
ffff88807a58af80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88807a58b000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807a58b080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88807a58b100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88807a58b180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess):
0: 23 00 and (%rax),%eax
2: 74 08 je 0xc
4: 4c 89 f7 mov %r14,%rdi
7: e8 20 aa 75 00 callq 0x75aa2c
c: f6 44 24 61 02 testb $0x2,0x61(%rsp)
11: 0f 85 76 01 00 00 jne 0x18d
17: 41 f7 c7 00 02 00 00 test $0x200,%r15d
1e: 74 01 je 0x21
20: fb sti
21: 48 c7 44 24 40 0e 36 movq $0x45e0360e,0x40(%rsp)
28: e0 45
* 2a: 4b c7 04 2c 00 00 00 movq $0x0,(%r12,%r13,1) <-- trapping instruction
31: 00
32: 43 c7 44 2c 09 00 00 movl $0x0,0x9(%r12,%r13,1)
39: 00 00
3b: 43 rex.XB
3c: c7 .byte 0xc7
3d: 44 2c 11 rex.R sub $0x11,%al


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[Alan Stern]

Oliver:

This looks like a bug in the anchor API.

This is the call to usb_anchor_resume_wakeups(). The call is made after
the completion handler callback. Evidently the xpad driver deallocated
the anchor during that time window. This can happen if the driver is
just waiting for its last URB to complete before freeing all its memory.

I don't know what the best solution is. It may be necessary to refcount
anchors somehow.

Alan Stern

[Oliver Neukum]

On 06.12.22 16:38, Alan Stern wrote:

Hi,

> Oliver:
>
> This looks like a bug in the anchor API.

Yes, it does.

Yes, complete() had run.

>
> I don't know what the best solution is. It may be necessary to refcount
> anchors somehow.

Then we cannot embed them anymore. Many drivers would need a lot of changes.
xpad included.

As far as I can tell the order we decrease use_count is correct. But:

6ec4147e7bdbd (Hans de Goede 2013-10-09 17:01:41 +0200 1674) usb_anchor_resume_wakeups(anchor);
94dfd7edfd5c9 (Ming Lei 2013-07-03 22:53:07 +0800 1675) atomic_dec(&urb->use_count);

Do we need to guarantee memory ordering here?

Regards
Oliver

[Alan Stern]

> > > __wake_up+0xf8/0x1c0 kernel/sched/wait.c:156
> > > __usb_hcd_giveback_urb+0x3a0/0x530 drivers/usb/core/hcd.c:1674
>
>
> > This is the call to usb_anchor_resume_wakeups(). The call is made after
> > the completion handler callback. Evidently the xpad driver deallocated
> > the anchor during that time window. This can happen if the driver is
> > just waiting for its last URB to complete before freeing all its memory.
>
> Yes, complete() had run.
> >
> > I don't know what the best solution is. It may be necessary to refcount
> > anchors somehow.
>
> Then we cannot embed them anymore. Many drivers would need a lot of changes.
> xpad included.

It's hard to tell what's really going on. Looking at
xpad_stop_output(), you see that it doesn't do anything if xpad->type is
XTYPE_UNKNOWN. Is that what happened here?

I can't figure out where the underlying race is. Maybe it's not
directly connected with anchors after all.

> As far as I can tell the order we decrease use_count is correct. But:
>
> 6ec4147e7bdbd (Hans de Goede 2013-10-09 17:01:41 +0200 1674) usb_anchor_resume_wakeups(anchor);
> 94dfd7edfd5c9 (Ming Lei 2013-07-03 22:53:07 +0800 1675) atomic_dec(&urb->use_count);
>
> Do we need to guarantee memory ordering here?

I don't think we need to do anything more. usb_kill_urb() is careful to
wait for completion handlers to finish, and we already have
smp_mb__after_atomic() barriers in the appropriate places to ensure
proper memory ordering.

Alan Stern

[Oliver Neukum]

On 08.12.22 18:40, Alan Stern wrote:
> On Thu, Dec 08, 2022 at 03:36:45PM +0100, Oliver Neukum wrote:
>> On 06.12.22 16:38, Alan Stern wrote:

> It's hard to tell what's really going on. Looking at
> xpad_stop_output(), you see that it doesn't do anything if xpad->type is
> XTYPE_UNKNOWN. Is that what happened here?

The output anchor in xpad was used. So I have to answer that in the negative.

> I can't figure out where the underlying race is. Maybe it's not
> directly connected with anchors after all.
>
>> As far as I can tell the order we decrease use_count is correct. But:
>>
>> 6ec4147e7bdbd (Hans de Goede 2013-10-09 17:01:41 +0200 1674) usb_anchor_resume_wakeups(anchor);
>> 94dfd7edfd5c9 (Ming Lei 2013-07-03 22:53:07 +0800 1675) atomic_dec(&urb->use_count);
>>
>> Do we need to guarantee memory ordering here?
>
> I don't think we need to do anything more. usb_kill_urb() is careful to
> wait for completion handlers to finish, and we already have

By checking use_count

> smp_mb__after_atomic() barriers in the appropriate places to ensure
> proper memory ordering.

Do we? Looking at __usb_hcd_giveback_urb():

usb_unanchor_urb(urb);

This is an implicit memory barrier

if (likely(status == 0))
usb_led_activity(USB_LED_EVENT_HOST);

/* pass ownership to the completion handler */
urb->status = status;
/*
* This function can be called in task context inside another remote
* coverage collection section, but kcov doesn't support that kind of
* recursion yet. Only collect coverage in softirq context for now.
*/
kcov_remote_start_usb_softirq((u64)urb->dev->bus->busnum);
urb->complete(urb);
kcov_remote_stop_softirq();

usb_anchor_resume_wakeups(anchor);
atomic_dec(&urb->use_count);
/*
* Order the write of urb->use_count above before the read
* of urb->reject below. Pairs with the memory barriers in
* usb_kill_urb() and usb_poison_urb().
*/
smp_mb__after_atomic();

That is the latest time use_count can go to zero.
But what is the earliest time the CPU could reorder setting use_count to zero?
Try as I might the last certain memory barrier I can find in this function
is usb_unanchor_urb().
That means another CPU can complete usb_kill_urb() before usb_anchor_resume_wakeups()
runs.

usb_anchor_resume_wakeups(anchor);

I think we need a memory barrier here, too.

atomic_dec(&urb->use_count);

Regards
Oliver

[Alan Stern]

Okay, how about if this is changed to atomic_dec_return? That puts a
full memory barrier both before and after the atomic decrement, so as a
bonus we could remove the smp_mb__after_atomic call.

Alan Stern

[Alan Stern]

Returning to an old discussion...

Please comment on the proposed patch below.

Alan Stern


Index: usb-devel/drivers/usb/core/hcd.c
===================================================================
--- usb-devel.orig/drivers/usb/core/hcd.c
+++ usb-devel/drivers/usb/core/hcd.c
@@ -1563,13 +1563,19 @@ int usb_hcd_submit_urb (struct urb *urb,
usbmon_urb_submit_error(&hcd->self, urb, status);
urb->hcpriv = NULL;
INIT_LIST_HEAD(&urb->urb_list);
- atomic_dec(&urb->use_count);
/*
- * Order the write of urb->use_count above before the read
- * of urb->reject below. Pairs with the memory barriers in
- * usb_kill_urb() and usb_poison_urb().
+ * urb->use_count acts like a refcount, so decrementing it to
+ * 0 must be ordered after earlier accesses (pairs with the
+ * implicit control dependencies in the wait conditions of
+ * usb_kill_urb() and usb_poison_urb()). Also, the decrement
+ * must be ordered before the read of urb->reject below
+ * (pairs with the memory barriers in those same routines).
+ *
+ * Get the effect of full memory barriers before and after
+ * the decrement by using atomic_dec_return() instead of a
+ * simple atomic_dec().
*/
- smp_mb__after_atomic();
+ atomic_dec_return(&urb->use_count);

atomic_dec(&urb->dev->urbnum);
if (atomic_read(&urb->reject))
@@ -1672,13 +1678,19 @@ static void __usb_hcd_giveback_urb(struc
kcov_remote_stop_softirq();

usb_anchor_resume_wakeups(anchor);
- atomic_dec(&urb->use_count);
/*
- * Order the write of urb->use_count above before the read
- * of urb->reject below. Pairs with the memory barriers in
- * usb_kill_urb() and usb_poison_urb().
+ * urb->use_count acts like a refcount, so decrementing it to
+ * 0 must be ordered after earlier accesses (pairs with the
+ * implicit control dependencies in the wait conditions of
+ * usb_kill_urb() and usb_poison_urb()). Also, the decrement
+ * must be ordered before the read of urb->reject below
+ * (pairs with the memory barriers in those same routines).
+ *
+ * Get the effect of full memory barriers before and after
+ * the decrement by using atomic_dec_return() instead of a
+ * simple atomic_dec().
*/
- smp_mb__after_atomic();
+ atomic_dec_return(&urb->use_count);

if (unlikely(atomic_read(&urb->reject)))
wake_up(&usb_kill_urb_queue);
Index: usb-devel/drivers/usb/core/urb.c
===================================================================
--- usb-devel.orig/drivers/usb/core/urb.c
+++ usb-devel/drivers/usb/core/urb.c
@@ -726,6 +726,10 @@ void usb_kill_urb(struct urb *urb)

usb_hcd_unlink_urb(urb, -ENOENT);
wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0);
+ /*
+ * The test of urb->use_count creates a control dependency
+ * ordering the wait_event() call against any later writes.
+ */

atomic_dec(&urb->reject);
}
@@ -776,6 +780,10 @@ void usb_poison_urb(struct urb *urb)

usb_hcd_unlink_urb(urb, -ENOENT);
wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0);
+ /*
+ * The test of urb->use_count creates a control dependency
+ * ordering the wait_event() call against any later writes.
+ */
}
EXPORT_SYMBOL_GPL(usb_poison_urb);

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.