Syzbot triggered a use after free in v5.5-rc6:
BUG: KASAN: use-after-free in v4l2_release+0x2f1/0x390 drivers/media/v4l2-core/v4l2-dev.c:459
Allocated by task 94:
usbvision_alloc drivers/media/usb/usbvision/usbvision-video.c:1315 [inline]
usbvision_probe.cold+0x5c5/0x1f21 drivers/media/usb/usbvision/usbvision-video.c:1469
Freed by task 1913:
kfree+0xd5/0x300 mm/slub.c:3957
usbvision_release+0x181/0x1c0 drivers/media/usb/usbvision/usbvision-video.c:1364
usbvision_radio_close.cold+0x2b/0x74 drivers/media/usb/usbvision/usbvision-video.c:1130
v4l2_release+0x2e7/0x390 drivers/media/v4l2-core/v4l2-dev.c:455
The problem is that the v4l2_release() calls usbvision_release() which
frees "usbvision" but v4l2_release() still wants to use
"usbvision->vdev". One solution is to make this devm_ allocated memory
so the memory isn't freed until later.
Reported-by: [email protected]
Signed-off-by: Dan Carpenter <[email protected]>
---
I copied this idea from a different driver, but I haven't tested it.
I wanted to try the #syz fix command to see if it works.
drivers/media/usb/usbvision/usbvision-video.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/drivers/media/usb/usbvision/usbvision-video.c b/drivers/media/usb/usbvision/usbvision-video.c
index 93d36aab824f..07b4763062c4 100644
--- a/drivers/media/usb/usbvision/usbvision-video.c
+++ b/drivers/media/usb/usbvision/usbvision-video.c
@@ -1312,7 +1312,7 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
{
struct usb_usbvision *usbvision;
- usbvision = kzalloc(sizeof(*usbvision), GFP_KERNEL);
+ usbvision = devm_kzalloc(&dev->dev, sizeof(*usbvision), GFP_KERNEL);
if (!usbvision)
return NULL;
@@ -1336,7 +1336,6 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
v4l2_ctrl_handler_free(&usbvision->hdl);
v4l2_device_unregister(&usbvision->v4l2_dev);
err_free:
- kfree(usbvision);
return NULL;
}
@@ -1361,7 +1360,6 @@ static void usbvision_release(struct usb_usbvision *usbvision)
v4l2_ctrl_handler_free(&usbvision->hdl);
v4l2_device_unregister(&usbvision->v4l2_dev);
- kfree(usbvision);
PDEBUG(DBG_PROBE, "success");
}
--
2.11.0
On 1/24/20 3:13 PM, Dan Carpenter wrote:
> Syzbot triggered a use after free in v5.5-rc6:
>
> BUG: KASAN: use-after-free in v4l2_release+0x2f1/0x390 drivers/media/v4l2-core/v4l2-dev.c:459
>
> Allocated by task 94:
> usbvision_alloc drivers/media/usb/usbvision/usbvision-video.c:1315 [inline]
> usbvision_probe.cold+0x5c5/0x1f21 drivers/media/usb/usbvision/usbvision-video.c:1469
>
> Freed by task 1913:
> kfree+0xd5/0x300 mm/slub.c:3957
> usbvision_release+0x181/0x1c0 drivers/media/usb/usbvision/usbvision-video.c:1364
> usbvision_radio_close.cold+0x2b/0x74 drivers/media/usb/usbvision/usbvision-video.c:1130
> v4l2_release+0x2e7/0x390 drivers/media/v4l2-core/v4l2-dev.c:455
>
> The problem is that the v4l2_release() calls usbvision_release() which
> frees "usbvision" but v4l2_release() still wants to use
> "usbvision->vdev". One solution is to make this devm_ allocated memory
> so the memory isn't freed until later.
devm_ allocated memory is freed after disconnect, so I doubt this will help, or at
best it will just move the problem elsewhere.
The right approach would be to use the release() callback from struct v4l2_device:
that's called when the very last open filehandle is closed.
But I'm not sure if it is worth the effort. The usbvision driver is a mess and
personally I think it should be deprecated.
Regards,
Hans
>
> Reported-by: [email protected]
> Signed-off-by: Dan Carpenter <[email protected]>
> ---
> I copied this idea from a different driver, but I haven't tested it.
> I wanted to try the #syz fix command to see if it works.
>
> drivers/media/usb/usbvision/usbvision-video.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/media/usb/usbvision/usbvision-video.c b/drivers/media/usb/usbvision/usbvision-video.c
> index 93d36aab824f..07b4763062c4 100644
> --- a/drivers/media/usb/usbvision/usbvision-video.c
> +++ b/drivers/media/usb/usbvision/usbvision-video.c
> @@ -1312,7 +1312,7 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
> {
> struct usb_usbvision *usbvision;
>
> - usbvision = kzalloc(sizeof(*usbvision), GFP_KERNEL);
> + usbvision = devm_kzalloc(&dev->dev, sizeof(*usbvision), GFP_KERNEL);
> if (!usbvision)
> return NULL;
>
> @@ -1336,7 +1336,6 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
> v4l2_ctrl_handler_free(&usbvision->hdl);
> v4l2_device_unregister(&usbvision->v4l2_dev);
> err_free:
> - kfree(usbvision);
> return NULL;
> }
>
> @@ -1361,7 +1360,6 @@ static void usbvision_release(struct usb_usbvision *usbvision)
>
> v4l2_ctrl_handler_free(&usbvision->hdl);
> v4l2_device_unregister(&usbvision->v4l2_dev);
> - kfree(usbvision);
>
> PDEBUG(DBG_PROBE, "success");
> }
>
Hi Hans,
On Fri, Feb 14, 2020 at 11:06:36AM +0100, Hans Verkuil wrote:
> On 1/24/20 3:13 PM, Dan Carpenter wrote:
> > Syzbot triggered a use after free in v5.5-rc6:
> >
> > BUG: KASAN: use-after-free in v4l2_release+0x2f1/0x390 drivers/media/v4l2-core/v4l2-dev.c:459
> >
> > Allocated by task 94:
> > usbvision_alloc drivers/media/usb/usbvision/usbvision-video.c:1315 [inline]
> > usbvision_probe.cold+0x5c5/0x1f21 drivers/media/usb/usbvision/usbvision-video.c:1469
> >
> > Freed by task 1913:
> > kfree+0xd5/0x300 mm/slub.c:3957
> > usbvision_release+0x181/0x1c0 drivers/media/usb/usbvision/usbvision-video.c:1364
> > usbvision_radio_close.cold+0x2b/0x74 drivers/media/usb/usbvision/usbvision-video.c:1130
> > v4l2_release+0x2e7/0x390 drivers/media/v4l2-core/v4l2-dev.c:455
> >
> > The problem is that the v4l2_release() calls usbvision_release() which
> > frees "usbvision" but v4l2_release() still wants to use
> > "usbvision->vdev". One solution is to make this devm_ allocated memory
> > so the memory isn't freed until later.
>
> devm_ allocated memory is freed after disconnect, so I doubt this will help, or at
> best it will just move the problem elsewhere.
Yes, devm_*alloc is evil :-( It has spread to many drivers and is used
incorrectly in most cases.
> The right approach would be to use the release() callback from struct v4l2_device:
> that's called when the very last open filehandle is closed.
Hillf Danton has sent a patch to do so in the "Re: KASAN: use-after-free
Read in v4l2_release (3)" thread. Have you seen it ?
> But I'm not sure if it is worth the effort. The usbvision driver is a mess and
> personally I think it should be deprecated.
I agree.
> > Reported-by: [email protected]
> > Signed-off-by: Dan Carpenter <[email protected]>
> > ---
> > I copied this idea from a different driver, but I haven't tested it.
> > I wanted to try the #syz fix command to see if it works.
> >
> > drivers/media/usb/usbvision/usbvision-video.c | 4 +---
> > 1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/drivers/media/usb/usbvision/usbvision-video.c b/drivers/media/usb/usbvision/usbvision-video.c
> > index 93d36aab824f..07b4763062c4 100644
> > --- a/drivers/media/usb/usbvision/usbvision-video.c
> > +++ b/drivers/media/usb/usbvision/usbvision-video.c
> > @@ -1312,7 +1312,7 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
> > {
> > struct usb_usbvision *usbvision;
> >
> > - usbvision = kzalloc(sizeof(*usbvision), GFP_KERNEL);
> > + usbvision = devm_kzalloc(&dev->dev, sizeof(*usbvision), GFP_KERNEL);
> > if (!usbvision)
> > return NULL;
> >
> > @@ -1336,7 +1336,6 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
> > v4l2_ctrl_handler_free(&usbvision->hdl);
> > v4l2_device_unregister(&usbvision->v4l2_dev);
> > err_free:
> > - kfree(usbvision);
> > return NULL;
> > }
> >
> > @@ -1361,7 +1360,6 @@ static void usbvision_release(struct usb_usbvision *usbvision)
> >
> > v4l2_ctrl_handler_free(&usbvision->hdl);
> > v4l2_device_unregister(&usbvision->v4l2_dev);
> > - kfree(usbvision);
> >
> > PDEBUG(DBG_PROBE, "success");
> > }
--
Regards,
Laurent Pinchart
On 2/14/20 12:22 PM, Laurent Pinchart wrote:
> Hi Hans,
>
> On Fri, Feb 14, 2020 at 11:06:36AM +0100, Hans Verkuil wrote:
>> On 1/24/20 3:13 PM, Dan Carpenter wrote:
>>> Syzbot triggered a use after free in v5.5-rc6:
>>>
>>> BUG: KASAN: use-after-free in v4l2_release+0x2f1/0x390 drivers/media/v4l2-core/v4l2-dev.c:459
>>>
>>> Allocated by task 94:
>>> usbvision_alloc drivers/media/usb/usbvision/usbvision-video.c:1315 [inline]
>>> usbvision_probe.cold+0x5c5/0x1f21 drivers/media/usb/usbvision/usbvision-video.c:1469
>>>
>>> Freed by task 1913:
>>> kfree+0xd5/0x300 mm/slub.c:3957
>>> usbvision_release+0x181/0x1c0 drivers/media/usb/usbvision/usbvision-video.c:1364
>>> usbvision_radio_close.cold+0x2b/0x74 drivers/media/usb/usbvision/usbvision-video.c:1130
>>> v4l2_release+0x2e7/0x390 drivers/media/v4l2-core/v4l2-dev.c:455
>>>
>>> The problem is that the v4l2_release() calls usbvision_release() which
>>> frees "usbvision" but v4l2_release() still wants to use
>>> "usbvision->vdev". One solution is to make this devm_ allocated memory
>>> so the memory isn't freed until later.
>>
>> devm_ allocated memory is freed after disconnect, so I doubt this will help, or at
>> best it will just move the problem elsewhere.
>
> Yes, devm_*alloc is evil :-( It has spread to many drivers and is used
> incorrectly in most cases.
>
>> The right approach would be to use the release() callback from struct v4l2_device:
>> that's called when the very last open filehandle is closed.
>
> Hillf Danton has sent a patch to do so in the "Re: KASAN: use-after-free
> Read in v4l2_release (3)" thread. Have you seen it ?
Ah, that was never mailed to linux-media, so never ended up in patchwork. And
if it ain't in patchwork, then I don't know about it :-)
Hillf, if you want your patch to be merged, then make sure it is CC-ed to
linux-media as well.
Regards,
Hans
>
>> But I'm not sure if it is worth the effort. The usbvision driver is a mess and
>> personally I think it should be deprecated.
>
> I agree.
>
>>> Reported-by: [email protected]
>>> Signed-off-by: Dan Carpenter <[email protected]>
>>> ---
>>> I copied this idea from a different driver, but I haven't tested it.
>>> I wanted to try the #syz fix command to see if it works.
>>>
>>> drivers/media/usb/usbvision/usbvision-video.c | 4 +---
>>> 1 file changed, 1 insertion(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/media/usb/usbvision/usbvision-video.c b/drivers/media/usb/usbvision/usbvision-video.c
>>> index 93d36aab824f..07b4763062c4 100644
>>> --- a/drivers/media/usb/usbvision/usbvision-video.c
>>> +++ b/drivers/media/usb/usbvision/usbvision-video.c
>>> @@ -1312,7 +1312,7 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
>>> {
>>> struct usb_usbvision *usbvision;
>>>
>>> - usbvision = kzalloc(sizeof(*usbvision), GFP_KERNEL);
>>> + usbvision = devm_kzalloc(&dev->dev, sizeof(*usbvision), GFP_KERNEL);
>>> if (!usbvision)
>>> return NULL;
>>>
>>> @@ -1336,7 +1336,6 @@ static struct usb_usbvision *usbvision_alloc(struct usb_device *dev,
>>> v4l2_ctrl_handler_free(&usbvision->hdl);
>>> v4l2_device_unregister(&usbvision->v4l2_dev);
>>> err_free:
>>> - kfree(usbvision);
>>> return NULL;
>>> }
>>>
>>> @@ -1361,7 +1360,6 @@ static void usbvision_release(struct usb_usbvision *usbvision)
>>>
>>> v4l2_ctrl_handler_free(&usbvision->hdl);
>>> v4l2_device_unregister(&usbvision->v4l2_dev);
>>> - kfree(usbvision);
>>>
>>> PDEBUG(DBG_PROBE, "success");
>>> }
>
On 2/14/20 1:14 PM, Hillf Danton wrote:
>
> On Fri, 14 Feb 2020 12:30:29 +0100 Hans Verkuil wrote:
>>
>> Hillf, if you want your patch to be merged, then make sure it is CC-ed to
>> linux-media as well.
>
> Please pick it up if it makes a sense to you and it was sent with
> linux-media added on the Cc list as it is known for a while that
> my mail agent is rejected @vger.kernel.org for what I am not clear
> about. It makes my day occasionally :P
I don't I ever received the full patch, only replies to your patch.
Please mail your patch directly to me so I have a clean version.
Regards,
Hans
>
> Thanks
> Hillf
>
On 2/14/20 1:48 PM, Hillf Danton wrote:
>
> On Fri, 14 Feb 2020 13:21:03 +0100 Hans Verkuil wrote:
>> On 2/14/20 1:14 PM, Hillf Danton wrote:
>>>
>>> On Fri, 14 Feb 2020 12:30:29 +0100 Hans Verkuil wrote:
>>>>
>>>> Hillf, if you want your patch to be merged, then make sure it is CC-ed to
>>>> linux-media as well.
>>>
>>> Please pick it up if it makes a sense to you and it was sent with
>>> linux-media added on the Cc list as it is known for a while that
>>> my mail agent is rejected @vger.kernel.org for what I am not clear
>>> about. It makes my day occasionally :P
>>
>> I don't I ever received the full patch, only replies to your patch.
>>
>
> =========
> Please take a look at the Cc tag in the snippet from
> https://lore.kernel.org/lkml/[email protected]/T/#m13f2c16b7cd1892f6a0b58b72ce37979cb6940b9
>
>
>> Subject: [PATCH] media: usbvision: add the release callback for video device
>> From: Hillf Danton <[email protected]>
>>
>> To fix the UAF syzbot reported,
>>
>> BUG: KASAN: use-after-free in v4l2_release+0x2f1/0x390 drivers/media/v4l2-core/v4l2-dev.c:459
>>
>> a release cb which is a simple wrapper of usbvision_release() is added
>> for releasing resources as the last reference to the usbvision video
>> device goes away.
>>
>> Reported-by: syzbot <[email protected]>
>> Fixes: 2aa689dd8057 ("[media] usbvision: embed video_device")
>> Cc: Hans Verkuil <[email protected]>
Ah, my work email. And I always delete posts mailed to that if it is also CC-ed
to linux-media. Which didn't actually arrive there in your case. And it's no longer
in my trash folder either.
So please mail me a properly formatted patch so I can forward it to linux-media
for you.
Regards,
Hans
>> Signed-off-by: Hillf Danton <[email protected]>
>> ---
> =========
>
>> Please mail your patch directly to me so I have a clean version.
>