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Date:   Thu, 27 Jun 2019 09:28:55 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Vandana BN <bnvandana@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     skhan@...uxfoundation.org, gregkh@...uxfoundation.org,
        linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] media:vivid: add sanity check to avoid divide error and
 set value to 1 if 0.

On 6/26/19 8:01 AM, Vandana BN wrote:
> Syzbot reported divide error in vivid_thread_vid_cap, which has been
> seen only once and doesnot have a reproducer.
> This patch sanity checks for the denominator value with WARN_ON if it is 0 and replaces it with 1.
> 
> Reported-by: syz...@...kaller.appspotmail.com
> 
> divide error: 0000 [#1] PREEMPT SMP KASAN
> kobject: 'tx-0' (0000000017161f7f): kobject_uevent_env
> CPU: 0 PID: 23689 Comm: vivid-003-vid-c Not tainted 5.0.0-rc4+ #58
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:vivid_cap_update_frame_period
> drivers/media/platform/vivid/vivid-kthread-cap.c:661 [inline]
> RIP: 0010:vivid_thread_vid_cap+0x221/0x284
> drivers/media/platform/vivid/vivid-kthread-cap.c:789
> Code: 48 c1 e9 03 0f b6 0c 11 48 89 f2 48 69 c0 00 ca 9a 3b 83 c2 03 38
> ca
> 7c 08 84 c9 0f 85 f0 1e 00 00 41 8b 8f 24 64 00 00 31 d2 <48> f7 f1 49
> 89
> c4 48 89 c3 49 8d 87 28 64 00 00 48 89 c2 48 89 45
> RSP: 0018:ffff88808b4afd68 EFLAGS: 00010246
> kobject: 'tx-0' (0000000017161f7f): fill_kobj_path: path
> = '/devices/virtual/net/gre0/queues/tx-0'
> RAX: 000000de5a6f8e00 RBX: 0000000100047b22 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000004
> RBP: ffff88808b4aff00 R08: ffff88804862e1c0 R09: ffffffff89997008
> R10: ffffffff89997010 R11: 0000000000000001 R12: 00000000fffffffc
> R13: ffff8880a17e0500 R14: ffff88803e40f760 R15: ffff8882182b0140
> FS:  0000000000000000(0000) GS:ffff8880ae800000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000004cdc90 CR3: 000000005d827000 CR4: 00000000001426f0
> Call Trace:
> kobject: 'gretap0' (00000000d7549098): kobject_add_internal: parent:
> 'net',
> set: 'devices'
> kobject: 'loop2' (0000000094ed4ee4): kobject_uevent_env
> kobject: 'loop2' (0000000094ed4ee4): fill_kobj_path: path
> = '/devices/virtual/block/loop2'
>   kthread+0x357/0x430 kernel/kthread.c:246
> kobject: 'gretap0' (00000000d7549098): kobject_uevent_env
>   ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
> Modules linked in:
> kobject: 'gretap0' (00000000d7549098): fill_kobj_path: path
> = '/devices/virtual/net/gretap0'
> ---[ end trace bc5c8b25b64d768f ]---
> kobject: 'loop1' (0000000032036b86): kobject_uevent_env
> RIP: 0010:vivid_cap_update_frame_period
> drivers/media/platform/vivid/vivid-kthread-cap.c:661 [inline]
> RIP: 0010:vivid_thread_vid_cap+0x221/0x2840
> drivers/media/platform/vivid/vivid-kthread-cap.c:789
> kobject: 'loop1' (0000000032036b86): fill_kobj_path: path
> = '/devices/virtual/block/loop1'
> Code: 48 c1 e9 03 0f b6 0c 11 48 89 f2 48 69 c0 00 ca 9a 3b 83 c2 03 38
> ca
> 7c 08 84 c9 0f 85 f0 1e 00 00 41 8b 8f 24 64 00 00 31 d2 <48> f7 f1 49
> 89
> c4 48 89 c3 49 8d 87 28 64 00 00 48 89 c2 48 89 45
> kobject: 'loop0' (00000000dd9927c3): kobject_uevent_env
> RSP: 0018:ffff88808b4afd68 EFLAGS: 00010246
> RAX: 000000de5a6f8e00 RBX: 0000000100047b22 RCX: 0000000000000000
> kobject: 'queues' (000000007ed20666): kobject_add_internal:
> parent: 'gretap0', set: '<NULL>'
> RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000004
> RBP: ffff88808b4aff00 R08: ffff88804862e1c0 R09: ffffffff89997008
> kobject: 'loop0' (00000000dd9927c3): fill_kobj_path: path
> = '/devices/virtual/block/loop0'
> R10: ffffffff89997010 R11: 0000000000000001 R12: 00000000fffffffc
> kobject: 'queues' (000000007ed20666): kobject_uevent_env
> R13: ffff8880a17e0500 R14: ffff88803e40f760 R15: ffff8882182b0140
> FS:  0000000000000000(0000) GS:ffff8880ae800000(0000)
> knlGS:0000000000000000
> kobject: 'loop5' (00000000a41f9e79): kobject_uevent_env
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> kobject: 'queues' (000000007ed20666): kobject_uevent_env: filter
> function
> caused the event to drop!
> CR2: 00000000004cdc90 CR3: 000000005d827000 CR4: 00000000001426f0
> kobject: 'loop5' (00000000a41f9e79): fill_kobj_path: path
> = '/devices/virtual/block/loop5'
> 
> Signed-off-by: Vandana BN <bnvandana@...il.com>
> ---
>  drivers/media/platform/vivid/vivid-kthread-cap.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/media/platform/vivid/vivid-kthread-cap.c b/drivers/media/platform/vivid/vivid-kthread-cap.c
> index f8006a30c12f..025a8c68bd1c 100644
> --- a/drivers/media/platform/vivid/vivid-kthread-cap.c
> +++ b/drivers/media/platform/vivid/vivid-kthread-cap.c
> @@ -658,6 +658,8 @@ static void vivid_cap_update_frame_period(struct vivid_dev *dev)
>  	u64 f_period;
>  
>  	f_period = (u64)dev->timeperframe_vid_cap.numerator * 1000000000;
> +	if(WARN_ON(dev->timeperframe_vid_cap.denominator == 0))
> +		dev->timeperframe_vid_cap.denominator = 1;
>  	do_div(f_period, dev->timeperframe_vid_cap.denominator);
>  	if (dev->field_cap == V4L2_FIELD_ALTERNATE)
>  		f_period >>= 1;
> 

Always run the patch over 'checkpatch.pl --strict'. It gives me:

WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#83:
This patch sanity checks for the denominator value with WARN_ON if it is 0 and replaces it with 1.

ERROR: space required before the open parenthesis '('
#175: FILE: drivers/media/platform/vivid/vivid-kthread-cap.c:661:
+       if(WARN_ON(dev->timeperframe_vid_cap.denominator == 0))

total: 1 errors, 1 warnings, 0 checks, 8 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

/home/hans/x.eml has style problems, please review.

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.

Regards,

	Hans

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