[PATCH] i2c: fix WARNING in pvr2_i2c_core_done

[B K Karthik]

#syz test: https://github.com/google/kasan.git usb-fuzzer

fix WARNING in pvr2_i2c_core_done by
unregistering device in the release handler
instead of the disconnect handler.

Reported-by: syzbot+e74a99...@syzkaller.appspotmail.com
Signed-off-by: B K Karthik <bkka...@pesu.pes.edu>
---
drivers/i2c/i2c-core-base.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 26f03a14a478..2d377d2e89f1 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -462,6 +462,7 @@ static void i2c_device_shutdown(struct device *dev)

static void i2c_client_dev_release(struct device *dev)
{
+ i2c_unregister_device(to_i2c_client(dev));
kfree(to_i2c_client(dev));
}

@@ -1527,7 +1528,6 @@ void i2c_del_adapter(struct i2c_adapter *adap)
dev_dbg(&adap->dev, "Removing %s at 0x%x\n", client->name,
client->addr);
list_del(&client->detected);
- i2c_unregister_device(client);
}
mutex_unlock(&adap->userspace_clients_lock);

--
2.20.1

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in kernfs_find_ns

pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
general protection fault, probably for non-canonical address 0xdffffc000000000e: 0000 [#1] SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000070-0x0000000000000077]
CPU: 0 PID: 78 Comm: pvrusb2-context Not tainted 5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:kernfs_find_ns+0x31/0x370 fs/kernfs/dir.c:829
Code: 49 89 d6 41 55 41 54 55 48 89 fd 53 48 83 ec 08 e8 f4 61 af ff 48 8d 7d 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 1e 03 00 00 48 8d bd 98 00 00 00 48 8b 5d 70 48
RSP: 0018:ffff8881d4187938 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffffffff863789c0 RCX: ffffffff85a79ba7
RDX: 000000000000000e RSI: ffffffff81901d1c RDI: 0000000000000070
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff873ed1e7
R10: fffffbfff0e7da3c R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff863790e0
FS: 0000000000000000(0000) GS:ffff8881db200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000557f2b45ae48 CR3: 00000001d2762000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
kernfs_find_and_get_ns+0x2f/0x60 fs/kernfs/dir.c:906
kernfs_find_and_get include/linux/kernfs.h:548 [inline]
sysfs_unmerge_group+0x5d/0x160 fs/sysfs/group.c:366
dpm_sysfs_remove+0x62/0xb0 drivers/base/power/sysfs.c:790
device_del+0x18b/0xd20 drivers/base/core.c:2834
device_unregister+0x22/0xc0 drivers/base/core.c:2889
i2c_unregister_device include/linux/err.h:41 [inline]
i2c_client_dev_release+0x39/0x50 drivers/i2c/i2c-core-base.c:465
device_release+0x71/0x200 drivers/base/core.c:1559
kobject_cleanup lib/kobject.c:693 [inline]
kobject_release lib/kobject.c:722 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x245/0x540 lib/kobject.c:739
put_device drivers/base/core.c:2779 [inline]
device_unregister+0x34/0xc0 drivers/base/core.c:2890
i2c_unregister_device+0x38/0x40 include/linux/err.h:41
v4l2_i2c_new_subdev_board+0x159/0x2c0 drivers/media/v4l2-core/v4l2-i2c.c:114
v4l2_i2c_new_subdev+0xb8/0xf0 drivers/media/v4l2-core/v4l2-i2c.c:135
pvr2_hdw_load_subdev drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2023 [inline]
pvr2_hdw_load_modules drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2075 [inline]
pvr2_hdw_setup_low drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2156 [inline]
pvr2_hdw_setup drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2262 [inline]
pvr2_hdw_initialize+0xc8d/0x3600 drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2339
pvr2_context_check drivers/media/usb/pvrusb2/pvrusb2-context.c:109 [inline]
pvr2_context_thread_func+0x250/0x850 drivers/media/usb/pvrusb2/pvrusb2-context.c:158
kthread+0x392/0x470 kernel/kthread.c:291
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:351
Modules linked in:
---[ end trace 9af941b6bcb04b01 ]---
RIP: 0010:kernfs_find_ns+0x31/0x370 fs/kernfs/dir.c:829
Code: 49 89 d6 41 55 41 54 55 48 89 fd 53 48 83 ec 08 e8 f4 61 af ff 48 8d 7d 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 1e 03 00 00 48 8d bd 98 00 00 00 48 8b 5d 70 48
RSP: 0018:ffff8881d4187938 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffffffff863789c0 RCX: ffffffff85a79ba7
RDX: 000000000000000e RSI: ffffffff81901d1c RDI: 0000000000000070
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff873ed1e7
R10: fffffbfff0e7da3c R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff863790e0
FS: 0000000000000000(0000) GS:ffff8881db200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000557f2b45ae48 CR3: 00000001d2762000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


Tested on:

commit: b791d1bd Merge tag 'locking-kcsan-2020-06-11' of git://git..
git tree: https://github.com/google/kasan.git usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=16dfe440900000
kernel config: https://syzkaller.appspot.com/x/.config?x=ccf1899337a6e343
dashboard link: https://syzkaller.appspot.com/bug?extid=e74a998ca8f1df9cc332
compiler: gcc (GCC) 10.1.0-syz 20200507
patch: https://syzkaller.appspot.com/x/patch.diff?x=117e281b100000

[B K Karthik]

On Tue, Jul 21, 2020 at 4:50 PM syzbot
<syzbot+e74a99...@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> general protection fault in kernfs_find_ns
>
> pvrusb2: Invalid write control endpoint
> pvrusb2: Invalid write control endpoint
> pvrusb2: Invalid write control endpoint
> pvrusb2: Invalid write control endpoint
> pvrusb2: Invalid write control endpoint
> pvrusb2: Invalid write control endpoint
> general protection fault, probably for non-canonical address 0xdffffc000000000e: 0000 [#1] SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000070-0x0000000000000077]

I'm guessing this has to do with kmem_cache_free() called by
i2c_acpi_remove_space_handler()
through acpi_ut_delete_generic_state() in drivers/acpi/osl.c:1708 ?

[B K Karthik]

#syz test: https://github.com/google/kasan.git usb-fuzzer

fix WARNING in pvr2_i2c_core_done by
unregistering device in the release handler

instead of the disconnect handler, setting the
linked flag after adding adapter to i2c,
and removing a call to acpi_ut_delete_generic_state()

Reported-by: syzbot+e74a99...@syzkaller.appspotmail.com
Signed-off-by: B K Karthik <bkka...@pesu.pes.edu>
---

v1 -> v2:
remove a call to acpi_ut_delete_generic state
and set linked flag after adding adapter to
i2c as suggested by Hillf Danton <hda...@sina.com>

drivers/acpi/acpica/utdelete.c | 5 -----
drivers/i2c/i2c-core-base.c | 2 +-
drivers/media/usb/pvrusb2/pvrusb2-i2c-core.c | 4 ++--
3 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/acpi/acpica/utdelete.c b/drivers/acpi/acpica/utdelete.c
index c365faf4e6cd..e36f51725854 100644
--- a/drivers/acpi/acpica/utdelete.c
+++ b/drivers/acpi/acpica/utdelete.c
@@ -648,11 +648,6 @@ acpi_ut_update_object_reference(union acpi_operand_object *object, u16 action)

/* Free any stacked Update State objects */

- while (state_list) {
- state = acpi_ut_pop_generic_state(&state_list);
- acpi_ut_delete_generic_state(state);
- }
-
return (status);

}

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 26f03a14a478..2d377d2e89f1 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -462,6 +462,7 @@ static void i2c_device_shutdown(struct device *dev)

static void i2c_client_dev_release(struct device *dev)
{
+ i2c_unregister_device(to_i2c_client(dev));
kfree(to_i2c_client(dev));
}

@@ -1527,7 +1528,6 @@ void i2c_del_adapter(struct i2c_adapter *adap)
dev_dbg(&adap->dev, "Removing %s at 0x%x\n", client->name,
client->addr);
list_del(&client->detected);
- i2c_unregister_device(client);
}
mutex_unlock(&adap->userspace_clients_lock);

diff --git a/drivers/media/usb/pvrusb2/pvrusb2-i2c-core.c b/drivers/media/usb/pvrusb2/pvrusb2-i2c-core.c
index 63db04fe12d3..09b2c878f459 100644
--- a/drivers/media/usb/pvrusb2/pvrusb2-i2c-core.c
+++ b/drivers/media/usb/pvrusb2/pvrusb2-i2c-core.c
@@ -623,9 +623,9 @@ void pvr2_i2c_core_init(struct pvr2_hdw *hdw)
hdw->i2c_adap.dev.parent = &hdw->usb_dev->dev;
hdw->i2c_adap.algo = &hdw->i2c_algo;
hdw->i2c_adap.algo_data = hdw;
- hdw->i2c_linked = !0;
i2c_set_adapdata(&hdw->i2c_adap, &hdw->v4l2_dev);
- i2c_add_adapter(&hdw->i2c_adap);
+ if (!i2c_add_adapter(&hdw->i2c_adap))
+ hdw->i2c_linked =!0;
if (hdw->i2c_func[0x18] == i2c_24xxx_ir) {
/* Probe for a different type of IR receiver on this
device. This is really the only way to differentiate
--
2.20.1

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in kernfs_find_ns

pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint

general protection fault, probably for non-canonical address 0xdffffc000000000e: 0000 [#1] SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000070-0x0000000000000077]

CPU: 0 PID: 78 Comm: pvrusb2-context Not tainted 5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:kernfs_find_ns+0x31/0x370 fs/kernfs/dir.c:829
Code: 49 89 d6 41 55 41 54 55 48 89 fd 53 48 83 ec 08 e8 f4 61 af ff 48 8d 7d 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 1e 03 00 00 48 8d bd 98 00 00 00 48 8b 5d 70 48

RSP: 0018:ffff8881d419f938 EFLAGS: 00010202

RAX: dffffc0000000000 RBX: ffffffff863789c0 RCX: ffffffff85a79ba7
RDX: 000000000000000e RSI: ffffffff81901d1c RDI: 0000000000000070
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff873ed1e7
R10: fffffbfff0e7da3c R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff863790e0
FS: 0000000000000000(0000) GS:ffff8881db200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f3a7e248000 CR3: 00000001d2224000 CR4: 00000000001406f0

---[ end trace a2576a16aa8e791c ]---

RIP: 0010:kernfs_find_ns+0x31/0x370 fs/kernfs/dir.c:829
Code: 49 89 d6 41 55 41 54 55 48 89 fd 53 48 83 ec 08 e8 f4 61 af ff 48 8d 7d 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 1e 03 00 00 48 8d bd 98 00 00 00 48 8b 5d 70 48

RSP: 0018:ffff8881d419f938 EFLAGS: 00010202

RAX: dffffc0000000000 RBX: ffffffff863789c0 RCX: ffffffff85a79ba7
RDX: 000000000000000e RSI: ffffffff81901d1c RDI: 0000000000000070
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff873ed1e7
R10: fffffbfff0e7da3c R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff863790e0
FS: 0000000000000000(0000) GS:ffff8881db200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f3a7e248000 CR3: 00000001d2224000 CR4: 00000000001406f0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


Tested on:

commit: b791d1bd Merge tag 'locking-kcsan-2020-06-11' of git://git..
git tree: https://github.com/google/kasan.git usb-fuzzer

console output: https://syzkaller.appspot.com/x/log.txt?x=1208f437100000

kernel config: https://syzkaller.appspot.com/x/.config?x=ccf1899337a6e343
dashboard link: https://syzkaller.appspot.com/bug?extid=e74a998ca8f1df9cc332
compiler: gcc (GCC) 10.1.0-syz 20200507

patch: https://syzkaller.appspot.com/x/patch.diff?x=14d56430900000

[Hillf Danton]

From: syzbot <syzbot+e74a99...@syzkaller.appspotmail.com>

Tue, 21 Jul 2020 21:06:10 -0700

[3]

> device_del+0x18b/0xd20 drivers/base/core.c:2834
> device_unregister+0x22/0xc0 drivers/base/core.c:2889
> i2c_unregister_device include/linux/err.h:41 [inline]

[2]

> i2c_client_dev_release+0x39/0x50 drivers/i2c/i2c-core-base.c:465
> device_release+0x71/0x200 drivers/base/core.c:1559

[1] kobject_del() goes before the release cb in kobject_cleanup() and
kobj is removed from sysfs, see [3] above.

> kobject_cleanup lib/kobject.c:693 [inline]
> kobject_release lib/kobject.c:722 [inline]
> kref_put include/linux/kref.h:65 [inline]
> kobject_put+0x245/0x540 lib/kobject.c:739
> put_device drivers/base/core.c:2779 [inline]
> device_unregister+0x34/0xc0 drivers/base/core.c:2890
> i2c_unregister_device+0x38/0x40 include/linux/err.h:41

Once is enough, see [2] above.

[B K Karthik]

Oh, thank you for letting me know about this. Forgive me, but I did
not understand you very clearly.
I presume you are saying that the second call to
i2c_unregister_device() is where the problem occurs?

please let me know.
thanks,

karthik

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in kernfs_find_ns

pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
pvrusb2: Invalid write control endpoint
general protection fault, probably for non-canonical address 0xdffffc000000000e: 0000 [#1] SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000070-0x0000000000000077]

CPU: 1 PID: 77 Comm: pvrusb2-context Not tainted 5.7.0-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:kernfs_find_ns+0x31/0x370 fs/kernfs/dir.c:829
Code: 49 89 d6 41 55 41 54 55 48 89 fd 53 48 83 ec 08 e8 f4 61 af ff 48 8d 7d 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 1e 03 00 00 48 8d bd 98 00 00 00 48 8b 5d 70 48

RSP: 0018:ffff8881d4147938 EFLAGS: 00010202

RAX: dffffc0000000000 RBX: ffffffff863789c0 RCX: ffffffff85a79ba7
RDX: 000000000000000e RSI: ffffffff81901d1c RDI: 0000000000000070
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff873ed1e7
R10: fffffbfff0e7da3c R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff863790e0

FS: 0000000000000000(0000) GS:ffff8881db300000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f06b6cea710 CR3: 00000001d0580000 CR4: 00000000001406e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
kernfs_find_and_get_ns+0x2f/0x60 fs/kernfs/dir.c:906
kernfs_find_and_get include/linux/kernfs.h:548 [inline]
sysfs_unmerge_group+0x5d/0x160 fs/sysfs/group.c:366
dpm_sysfs_remove+0x62/0xb0 drivers/base/power/sysfs.c:790

device_del+0x18b/0xd20 drivers/base/core.c:2834
device_unregister+0x22/0xc0 drivers/base/core.c:2889
i2c_unregister_device include/linux/err.h:41 [inline]

i2c_client_dev_release+0x39/0x40 drivers/i2c/i2c-core-base.c:465
device_release+0x71/0x200 drivers/base/core.c:1559

kobject_cleanup lib/kobject.c:693 [inline]
kobject_release lib/kobject.c:722 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x245/0x540 lib/kobject.c:739
put_device drivers/base/core.c:2779 [inline]
device_unregister+0x34/0xc0 drivers/base/core.c:2890
i2c_unregister_device+0x38/0x40 include/linux/err.h:41

v4l2_i2c_new_subdev_board+0x159/0x2c0 drivers/media/v4l2-core/v4l2-i2c.c:114
v4l2_i2c_new_subdev+0xb8/0xf0 drivers/media/v4l2-core/v4l2-i2c.c:135
pvr2_hdw_load_subdev drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2023 [inline]
pvr2_hdw_load_modules drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2075 [inline]
pvr2_hdw_setup_low drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2156 [inline]
pvr2_hdw_setup drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2262 [inline]
pvr2_hdw_initialize+0xc8d/0x3600 drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2339
pvr2_context_check drivers/media/usb/pvrusb2/pvrusb2-context.c:109 [inline]
pvr2_context_thread_func+0x250/0x850 drivers/media/usb/pvrusb2/pvrusb2-context.c:158
kthread+0x392/0x470 kernel/kthread.c:291
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:351

Modules linked in:
---[ end trace 039fb744ac5861de ]---

RIP: 0010:kernfs_find_ns+0x31/0x370 fs/kernfs/dir.c:829
Code: 49 89 d6 41 55 41 54 55 48 89 fd 53 48 83 ec 08 e8 f4 61 af ff 48 8d 7d 70 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 1e 03 00 00 48 8d bd 98 00 00 00 48 8b 5d 70 48

RSP: 0018:ffff8881d4147938 EFLAGS: 00010202

RAX: dffffc0000000000 RBX: ffffffff863789c0 RCX: ffffffff85a79ba7
RDX: 000000000000000e RSI: ffffffff81901d1c RDI: 0000000000000070
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff873ed1e7
R10: fffffbfff0e7da3c R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff863790e0

FS: 0000000000000000(0000) GS:ffff8881db300000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f06b6cea710 CR3: 00000001d0580000 CR4: 00000000001406e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Tested on:

commit: b791d1bd Merge tag 'locking-kcsan-2020-06-11' of git://git..
git tree: https://github.com/google/kasan.git usb-fuzzer

console output: https://syzkaller.appspot.com/x/log.txt?x=12a533c8900000

kernel config: https://syzkaller.appspot.com/x/.config?x=ccf1899337a6e343
dashboard link: https://syzkaller.appspot.com/bug?extid=e74a998ca8f1df9cc332
compiler: gcc (GCC) 10.1.0-syz 20200507

patch: https://syzkaller.appspot.com/x/patch.diff?x=140ec1ef100000

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

drivers/media/v4l2-core/v4l2-i2c.c:114:3: error: implicit declaration of function 'i2c_client_dev_release' [-Werror=implicit-function-declaration]

Tested on:

commit: b791d1bd Merge tag 'locking-kcsan-2020-06-11' of git://git..
git tree: https://github.com/google/kasan.git usb-fuzzer

dashboard link: https://syzkaller.appspot.com/bug?extid=e74a998ca8f1df9cc332
compiler: gcc (GCC) 10.1.0-syz 20200507

patch: https://syzkaller.appspot.com/x/patch.diff?x=15083f5f100000