[Linux-kernel-mentees] [REQUEST] for assistance with fixing WARNING in pvr2_i2c_core_done

B K Karthik bkkarthik at pesu.pes.edu
Fri Jul 24 03:42:27 UTC 2020


hi,

I've been looking at https://syzkaller.appspot.com/bug?extid=e74a998ca8f1df9cc332 for quite some time now.
I think I will be able to fix it with a little assistance.

I was able to reproduce it, and as er suggestions I tried to unregister the device in the release handler instead of the disconnect handler.
I tried a few things, but they triggered a general protection fault in kernfs_find_ns()

Hillf Danton <hdanton at sina.com> said the following. 

> 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
> 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

[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.

can you give me a suggestion as to how I am supposed to go about fixing this bug?

thanks,

karthik
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