WARNING: Support for this device (Terratec Grabster AV400) is experimental.

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 9a33b369 usb-fuzzer: main usb gadget fuzzer driver
git tree: https://github.com/google/kasan.git usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=141ca62d200000
kernel config: https://syzkaller.appspot.com/x/.config?x=23e37f59d94ddd15
dashboard link: https://syzkaller.appspot.com/bug?extid=af8f8d2ac0d39b0ed3a0
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1405bedd200000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13ce3bbb200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+af8f8d...@syzkaller.appspotmail.com

usb 1-1: New USB device found, idVendor=0ccd, idProduct=0039, bcdDevice=
d.3c
usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 1-1: config 0 descriptor??
pvrusb2: Hardware description: Terratec Grabster AV400
pvrusb2: **********
pvrusb2: WARNING: Support for this device (Terratec Grabster AV400) is
experimental.
pvrusb2: Important functionality might not be entirely working.
pvrusb2: Please consider contacting the driver author to help with further
stabilization of the driver.
pvrusb2: **********


---
This bug 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 bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Alan Stern]

This does seem like a bug in syzbot. Why does it think this pr_info()
output indicates a crash? Is it fooled by the capitalized "WARNING" at
the start of one of the lines?

Alan Stern

[Andrey Konovalov]

Well, as of [1] WARN*() should only be used to indicate a kernel bug.
Normally, WARN*() prints a line that start with a warning, which is
followed by a stack trace. Unfortunately the stack trace is not always
present (kernel memory is badly corrupted, console deadlocked, etc.),
so syzbot detects the "WARNING:" line as a beginning of a WARN*()
reported bug. In this case the driver does something like
`pr_info("WARNING: ...", ...)`, which confuses syzbot. I'd say it's
the kernel that needs to be changed here to use some other kind of
prefix for printing warning messages.

[1] https://github.com/torvalds/linux/commit/96c6a32ccb55a366054fd82cc63523bb7f7493d3

[Greg KH]

Ok, we can change these to "Warning" then. Want to send a patch?

thanks,

greg k-h

[Andrey Konovalov]

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

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer still triggered
crash:
WARNING in sysfs_remove_group

pvrusb2: Important functionality might not be entirely working.
pvrusb2: Please consider contacting the driver author to help with further
stabilization of the driver.

------------[ cut here ]------------
pvrusb2: **********
sysfs group 'power' not found for kobject '0-0044'
WARNING: CPU: 0 PID: 586 at fs/sysfs/group.c:254 sysfs_remove_group
fs/sysfs/group.c:254 [inline]
WARNING: CPU: 0 PID: 586 at fs/sysfs/group.c:254
sysfs_remove_group+0x15a/0x1b0 fs/sysfs/group.c:245
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 586 Comm: pvrusb2-context Not tainted 5.1.0-rc3-g43151d6-dirty
#1
usb 5-1: New USB device found, idVendor=0ccd, idProduct=0039, bcdDevice=
d.3c
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0xe8/0x16e lib/dump_stack.c:113
panic+0x29d/0x5f2 kernel/panic.c:214
__warn.cold+0x20/0x48 kernel/panic.c:571
report_bug+0x262/0x2a0 lib/bug.c:186
fixup_bug arch/x86/kernel/traps.c:179 [inline]
fixup_bug arch/x86/kernel/traps.c:174 [inline]
do_error_trap+0x130/0x1f0 arch/x86/kernel/traps.c:272
do_invalid_op+0x37/0x40 arch/x86/kernel/traps.c:291
invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:sysfs_remove_group fs/sysfs/group.c:254 [inline]
RIP: 0010:sysfs_remove_group+0x15a/0x1b0 fs/sysfs/group.c:245
Code: 48 89 d9 49 8b 14 24 48 b8 00 00 00 00 00 fc ff df 48 c1 e9 03 80 3c
01 00 75 41 48 8b 33 48 c7 c7 a0 31 7a 8e e8 e6 c2 6e ff <0f> 0b eb 95 e8
0d de d3 ff e9 d2 fe ff ff 48 89 df e8 00 de d3 ff
RSP: 0018:ffff88809cc9fb70 EFLAGS: 00010286
RAX: 0000000000000000 RBX: ffffffff8f037e80 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815b2132 RDI: ffffed1013993f60
RBP: 0000000000000000 R08: ffff88809cc93100 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888097d06eb0
R13: ffffffff8f038520 R14: 1ffff11013993f97 R15: ffff888097d06ea8
dpm_sysfs_remove+0xa2/0xc0 drivers/base/power/sysfs.c:737
device_del+0x175/0xb90 drivers/base/core.c:2246
device_unregister+0x27/0xd0 drivers/base/core.c:2301
i2c_unregister_device drivers/i2c/i2c-core-base.c:814 [inline]
__unregister_client drivers/i2c/i2c-core-base.c:1422 [inline]
__unregister_client+0x7d/0x90 drivers/i2c/i2c-core-base.c:1418
device_for_each_child+0x100/0x170 drivers/base/core.c:2401
i2c_del_adapter drivers/i2c/i2c-core-base.c:1485 [inline]
i2c_del_adapter+0x35b/0x640 drivers/i2c/i2c-core-base.c:1447
pvr2_i2c_core_done+0x6e/0xbb
drivers/media/usb/pvrusb2/pvrusb2-i2c-core.c:662
pvr2_hdw_destroy+0x17e/0x380 drivers/media/usb/pvrusb2/pvrusb2-hdw.c:2669
pvr2_context_destroy+0x89/0x240
drivers/media/usb/pvrusb2/pvrusb2-context.c:79
pvr2_context_check drivers/media/usb/pvrusb2/pvrusb2-context.c:146 [inline]
pvr2_context_thread_func+0x65e/0x870
drivers/media/usb/pvrusb2/pvrusb2-context.c:167
usb 5-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
kthread+0x313/0x420 kernel/kthread.c:253
usb 3-1: New USB device found, idVendor=0ccd, idProduct=0039, bcdDevice=
d.3c
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
Kernel Offset: disabled
Rebooting in 86400 seconds..


Tested on:

commit: 43151d6c usb-fuzzer: main usb gadget fuzzer driver

git tree: https://github.com/google/kasan.git usb-fuzzer

console output: https://syzkaller.appspot.com/x/log.txt?x=11e467a8a00000
kernel config: https://syzkaller.appspot.com/x/.config?x=274aad0cf966c3bc

compiler: gcc (GCC) 9.0.0 20181231 (experimental)

patch: https://syzkaller.appspot.com/x/patch.diff?x=1479a4b8a00000

[Andrey Konovalov]

Done.

>
> thanks,
>
> greg k-h