fbdev/xen-fbfront: Assign fb_info->device

Commit Message

Jason Andryuk Sept. 10, 2024, 2:09 a.m. UTC

From: Jason Andryuk <[e-mail]>

Probing xen-fbfront faults in video_is_primary_device().  The passed-in
struct device is NULL since xen-fbfront doesn't assign it and the
memory is kzalloc()-ed.  Assign fb_info->device to avoid this.

This was exposed by the conversion of fb_is_primary_device() to
video_is_primary_device() which dropped a NULL check for struct device.

Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
Reported-by: Arthur Borsboom <[e-mail]>
Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
Tested-by: Arthur Borsboom <[e-mail]>
CC: [e-mail]
Signed-off-by: Jason Andryuk <[e-mail]>
---
The other option would be to re-instate the NULL check in
video_is_primary_device()
---
 drivers/video/fbdev/xen-fbfront.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Roger Pau Monné Sept. 10, 2024, 7:22 a.m. UTC | #1

On Mon, Sep 09, 2024 at 10:09:16PM -0400, Jason Andryuk wrote:
> From: Jason Andryuk <[e-mail]>
> 
> Probing xen-fbfront faults in video_is_primary_device().  The passed-in
> struct device is NULL since xen-fbfront doesn't assign it and the
> memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
> 
> This was exposed by the conversion of fb_is_primary_device() to
> video_is_primary_device() which dropped a NULL check for struct device.
> 
> Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
> Reported-by: Arthur Borsboom <[e-mail]>
> Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
> Tested-by: Arthur Borsboom <[e-mail]>
> CC: [e-mail]
> Signed-off-by: Jason Andryuk <[e-mail]>

Reviewed-by: Roger Pau Monné <[e-mail]>

> ---
> The other option would be to re-instate the NULL check in
> video_is_primary_device()

I do think this is needed, or at least an explanation.  The commit
message in f178e96de7f0 doesn't mention anything about
video_is_primary_device() not allowing being passed a NULL device
(like it was possible with fb_is_primary_device()).

Otherwise callers of video_is_primary_device() would need to be
adjusted to check for device != NULL.

Thanks, Roger.

Thomas Zimmermann Sept. 10, 2024, 7:26 a.m. UTC | #2

Am 10.09.24 um 04:09 schrieb Jason Andryuk:
> From: Jason Andryuk <[e-mail]>
>
> Probing xen-fbfront faults in video_is_primary_device().  The passed-in
> struct device is NULL since xen-fbfront doesn't assign it and the
> memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
>
> This was exposed by the conversion of fb_is_primary_device() to
> video_is_primary_device() which dropped a NULL check for struct device.
>
> Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
> Reported-by: Arthur Borsboom <[e-mail]>
> Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
> Tested-by: Arthur Borsboom <[e-mail]>
> CC: [e-mail]
> Signed-off-by: Jason Andryuk <[e-mail]>

Reviewed-by: Thomas Zimmermann <[e-mail]>

Thanks a lot.

> ---
> The other option would be to re-instate the NULL check in
> video_is_primary_device()
> ---
>   drivers/video/fbdev/xen-fbfront.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/drivers/video/fbdev/xen-fbfront.c b/drivers/video/fbdev/xen-fbfront.c
> index 66d4628a96ae..c90f48ebb15e 100644
> --- a/drivers/video/fbdev/xen-fbfront.c
> +++ b/drivers/video/fbdev/xen-fbfront.c
> @@ -407,6 +407,7 @@ static int xenfb_probe(struct xenbus_device *dev,
>   	/* complete the abuse: */
>   	fb_info->pseudo_palette = fb_info->par;
>   	fb_info->par = info;
> +	fb_info->device = &dev->dev;
>   
>   	fb_info->screen_buffer = info->fb;
>

Thomas Zimmermann Sept. 10, 2024, 7:29 a.m. UTC | #3

Hi

Am 10.09.24 um 09:22 schrieb Roger Pau Monné:
> On Mon, Sep 09, 2024 at 10:09:16PM -0400, Jason Andryuk wrote:
>> From: Jason Andryuk <[e-mail]>
>>
>> Probing xen-fbfront faults in video_is_primary_device().  The passed-in
>> struct device is NULL since xen-fbfront doesn't assign it and the
>> memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
>>
>> This was exposed by the conversion of fb_is_primary_device() to
>> video_is_primary_device() which dropped a NULL check for struct device.
>>
>> Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
>> Reported-by: Arthur Borsboom <[e-mail]>
>> Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
>> Tested-by: Arthur Borsboom <[e-mail]>
>> CC: [e-mail]
>> Signed-off-by: Jason Andryuk <[e-mail]>
> Reviewed-by: Roger Pau Monné <[e-mail]>
>
>> ---
>> The other option would be to re-instate the NULL check in
>> video_is_primary_device()
> I do think this is needed, or at least an explanation.  The commit
> message in f178e96de7f0 doesn't mention anything about
> video_is_primary_device() not allowing being passed a NULL device
> (like it was possible with fb_is_primary_device()).
>
> Otherwise callers of video_is_primary_device() would need to be
> adjusted to check for device != NULL.

The helper expects a non-NULL pointer. We might want to document this.

Best regards
Thomas

>
> Thanks, Roger.
>

Roger Pau Monné Sept. 10, 2024, 8:13 a.m. UTC | #4

On Tue, Sep 10, 2024 at 09:29:30AM +0200, Thomas Zimmermann wrote:
> Hi
> 
> Am 10.09.24 um 09:22 schrieb Roger Pau Monné:
> > On Mon, Sep 09, 2024 at 10:09:16PM -0400, Jason Andryuk wrote:
> > > From: Jason Andryuk <[e-mail]>
> > > 
> > > Probing xen-fbfront faults in video_is_primary_device().  The passed-in
> > > struct device is NULL since xen-fbfront doesn't assign it and the
> > > memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
> > > 
> > > This was exposed by the conversion of fb_is_primary_device() to
> > > video_is_primary_device() which dropped a NULL check for struct device.
> > > 
> > > Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
> > > Reported-by: Arthur Borsboom <[e-mail]>
> > > Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
> > > Tested-by: Arthur Borsboom <[e-mail]>
> > > CC: [e-mail]
> > > Signed-off-by: Jason Andryuk <[e-mail]>
> > Reviewed-by: Roger Pau Monné <[e-mail]>
> > 
> > > ---
> > > The other option would be to re-instate the NULL check in
> > > video_is_primary_device()
> > I do think this is needed, or at least an explanation.  The commit
> > message in f178e96de7f0 doesn't mention anything about
> > video_is_primary_device() not allowing being passed a NULL device
> > (like it was possible with fb_is_primary_device()).
> > 
> > Otherwise callers of video_is_primary_device() would need to be
> > adjusted to check for device != NULL.
> 
> The helper expects a non-NULL pointer. We might want to document this.

A BUG_ON(!dev); might be enough documentation that the function
expected a non-NULL dev IMO.

Thanks, Roger.

Greg KH Sept. 10, 2024, 8:33 a.m. UTC | #5

On Tue, Sep 10, 2024 at 10:13:01AM +0200, Roger Pau Monné wrote:
> On Tue, Sep 10, 2024 at 09:29:30AM +0200, Thomas Zimmermann wrote:
> > Hi
> > 
> > Am 10.09.24 um 09:22 schrieb Roger Pau Monné:
> > > On Mon, Sep 09, 2024 at 10:09:16PM -0400, Jason Andryuk wrote:
> > > > From: Jason Andryuk <[e-mail]>
> > > > 
> > > > Probing xen-fbfront faults in video_is_primary_device().  The passed-in
> > > > struct device is NULL since xen-fbfront doesn't assign it and the
> > > > memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
> > > > 
> > > > This was exposed by the conversion of fb_is_primary_device() to
> > > > video_is_primary_device() which dropped a NULL check for struct device.
> > > > 
> > > > Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
> > > > Reported-by: Arthur Borsboom <[e-mail]>
> > > > Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
> > > > Tested-by: Arthur Borsboom <[e-mail]>
> > > > CC: [e-mail]
> > > > Signed-off-by: Jason Andryuk <[e-mail]>
> > > Reviewed-by: Roger Pau Monné <[e-mail]>
> > > 
> > > > ---
> > > > The other option would be to re-instate the NULL check in
> > > > video_is_primary_device()
> > > I do think this is needed, or at least an explanation.  The commit
> > > message in f178e96de7f0 doesn't mention anything about
> > > video_is_primary_device() not allowing being passed a NULL device
> > > (like it was possible with fb_is_primary_device()).
> > > 
> > > Otherwise callers of video_is_primary_device() would need to be
> > > adjusted to check for device != NULL.
> > 
> > The helper expects a non-NULL pointer. We might want to document this.
> 
> A BUG_ON(!dev); might be enough documentation that the function
> expected a non-NULL dev IMO.

No need for that, don't check for things that will never happen.

Arthur Borsboom Sept. 10, 2024, 12:18 p.m. UTC | #6

On Tue, 10 Sept 2024 at 10:33, Greg KH <[e-mail]> wrote:
>
> On Tue, Sep 10, 2024 at 10:13:01AM +0200, Roger Pau Monné wrote:
> > On Tue, Sep 10, 2024 at 09:29:30AM +0200, Thomas Zimmermann wrote:
> > > Hi
> > >
> > > Am 10.09.24 um 09:22 schrieb Roger Pau Monné:
> > > > On Mon, Sep 09, 2024 at 10:09:16PM -0400, Jason Andryuk wrote:
> > > > > From: Jason Andryuk <[e-mail]>
> > > > >
> > > > > Probing xen-fbfront faults in video_is_primary_device().  The passed-in
> > > > > struct device is NULL since xen-fbfront doesn't assign it and the
> > > > > memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
> > > > >
> > > > > This was exposed by the conversion of fb_is_primary_device() to
> > > > > video_is_primary_device() which dropped a NULL check for struct device.
> > > > >
> > > > > Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
> > > > > Reported-by: Arthur Borsboom <[e-mail]>
> > > > > Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
> > > > > Tested-by: Arthur Borsboom <[e-mail]>
> > > > > CC: [e-mail]
> > > > > Signed-off-by: Jason Andryuk <[e-mail]>
> > > > Reviewed-by: Roger Pau Monné <[e-mail]>
> > > >
> > > > > ---
> > > > > The other option would be to re-instate the NULL check in
> > > > > video_is_primary_device()
> > > > I do think this is needed, or at least an explanation.  The commit
> > > > message in f178e96de7f0 doesn't mention anything about
> > > > video_is_primary_device() not allowing being passed a NULL device
> > > > (like it was possible with fb_is_primary_device()).
> > > >
> > > > Otherwise callers of video_is_primary_device() would need to be
> > > > adjusted to check for device != NULL.
> > >
> > > The helper expects a non-NULL pointer. We might want to document this.
> >
> > A BUG_ON(!dev); might be enough documentation that the function
> > expected a non-NULL dev IMO.
>
> No need for that, don't check for things that will never happen.

And yet, here we are, me reporting a kernel/VM crash due to a thing
that will never happen, see 'Closes' above.

I don't want to suggest BUG_ON is the right approach; I have no idea.
I just want to mention that (!dev) did happen. :-)

Greg KH Sept. 10, 2024, 12:22 p.m. UTC | #7

On Tue, Sep 10, 2024 at 02:18:35PM +0200, Arthur Borsboom wrote:
> On Tue, 10 Sept 2024 at 10:33, Greg KH <[e-mail]> wrote:
> >
> > On Tue, Sep 10, 2024 at 10:13:01AM +0200, Roger Pau Monné wrote:
> > > On Tue, Sep 10, 2024 at 09:29:30AM +0200, Thomas Zimmermann wrote:
> > > > Hi
> > > >
> > > > Am 10.09.24 um 09:22 schrieb Roger Pau Monné:
> > > > > On Mon, Sep 09, 2024 at 10:09:16PM -0400, Jason Andryuk wrote:
> > > > > > From: Jason Andryuk <[e-mail]>
> > > > > >
> > > > > > Probing xen-fbfront faults in video_is_primary_device().  The passed-in
> > > > > > struct device is NULL since xen-fbfront doesn't assign it and the
> > > > > > memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
> > > > > >
> > > > > > This was exposed by the conversion of fb_is_primary_device() to
> > > > > > video_is_primary_device() which dropped a NULL check for struct device.
> > > > > >
> > > > > > Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
> > > > > > Reported-by: Arthur Borsboom <[e-mail]>
> > > > > > Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
> > > > > > Tested-by: Arthur Borsboom <[e-mail]>
> > > > > > CC: [e-mail]
> > > > > > Signed-off-by: Jason Andryuk <[e-mail]>
> > > > > Reviewed-by: Roger Pau Monné <[e-mail]>
> > > > >
> > > > > > ---
> > > > > > The other option would be to re-instate the NULL check in
> > > > > > video_is_primary_device()
> > > > > I do think this is needed, or at least an explanation.  The commit
> > > > > message in f178e96de7f0 doesn't mention anything about
> > > > > video_is_primary_device() not allowing being passed a NULL device
> > > > > (like it was possible with fb_is_primary_device()).
> > > > >
> > > > > Otherwise callers of video_is_primary_device() would need to be
> > > > > adjusted to check for device != NULL.
> > > >
> > > > The helper expects a non-NULL pointer. We might want to document this.
> > >
> > > A BUG_ON(!dev); might be enough documentation that the function
> > > expected a non-NULL dev IMO.
> >
> > No need for that, don't check for things that will never happen.
> 
> And yet, here we are, me reporting a kernel/VM crash due to a thing
> that will never happen, see 'Closes' above.
> 
> I don't want to suggest BUG_ON is the right approach; I have no idea.
> I just want to mention that (!dev) did happen. :-)

A BUG_ON() will cause the same crash, so I don't see your point, sorry.

greg k-h

Helge Deller Sept. 11, 2024, 5:59 a.m. UTC | #8

On 9/10/24 04:09, Jason Andryuk wrote:
> From: Jason Andryuk <[e-mail]>
>
> Probing xen-fbfront faults in video_is_primary_device().  The passed-in
> struct device is NULL since xen-fbfront doesn't assign it and the
> memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
>
> This was exposed by the conversion of fb_is_primary_device() to
> video_is_primary_device() which dropped a NULL check for struct device.
>
> Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
> Reported-by: Arthur Borsboom <[e-mail]>
> Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
> Tested-by: Arthur Borsboom <[e-mail]>
> CC: [e-mail]
> Signed-off-by: Jason Andryuk <[e-mail]>

applied to fbdev git tree.

Thanks!
Helge

Patch

diff --git a/drivers/video/fbdev/xen-fbfront.c b/drivers/video/fbdev/xen-fbfront.c
index 66d4628a96ae..c90f48ebb15e 100644
--- a/drivers/video/fbdev/xen-fbfront.c
+++ b/drivers/video/fbdev/xen-fbfront.c
@@ -407,6 +407,7 @@  static int xenfb_probe(struct xenbus_device *dev,
 	/* complete the abuse: */
 	fb_info->pseudo_palette = fb_info->par;
 	fb_info->par = info;
+	fb_info->device = &dev->dev;
 
 	fb_info->screen_buffer = info->fb;