[PATCH] drm/managed: Fix off-by-one in warning

[PATCH] drm/managed: Fix off-by-one in warning

[Daniel Vetter]

I'm thinking this is the warning that fired in the 0day report, but I
can't double-check yet since 0day didn't upload its source tree
anywhere I can check. And all the drivers I can easily test don't use
drm_dev_alloc anymore ...

Also if I'm correct supreme amounts of bad luck because usually kslap
(for bigger structures) gives us something quite a bit bigger than
what we asked for.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: c6603c740e0e ("drm: add managed resources tied to drm_device")
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Neil Armstrong <narmstrong@baylibre.com
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 drivers/gpu/drm/drm_managed.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
index 4955241ceb4c..9cebfe370a65 100644
--- a/drivers/gpu/drm/drm_managed.c
+++ b/drivers/gpu/drm/drm_managed.c
@@ -139,8 +139,7 @@ void drmm_add_final_kfree(struct drm_device *dev, void *container)
 {
 	WARN_ON(dev->managed.final_kfree);
 	WARN_ON(dev < (struct drm_device *) container);
-	WARN_ON(dev + 1 >=
-		(struct drm_device *) (container + ksize(container)));
+	WARN_ON(dev + 1 > (struct drm_device *) (container + ksize(container)));
 	dev->managed.final_kfree = container;
 }
 EXPORT_SYMBOL(drmm_add_final_kfree);
-- 
2.25.1

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Re: [PATCH] drm/managed: Fix off-by-one in warning

[Sam Ravnborg]

Hi Daniel.

On Sat, Mar 28, 2020 at 05:23:58PM +0100, Daniel Vetter wrote:
> I'm thinking this is the warning that fired in the 0day report, but I
> can't double-check yet since 0day didn't upload its source tree
> anywhere I can check. And all the drivers I can easily test don't use
> drm_dev_alloc anymore ...
> 
> Also if I'm correct supreme amounts of bad luck because usually kslap
> (for bigger structures) gives us something quite a bit bigger than
> what we asked for.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Fixes: c6603c740e0e ("drm: add managed resources tied to drm_device")
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Neil Armstrong <narmstrong@baylibre.com
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_managed.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
> index 4955241ceb4c..9cebfe370a65 100644
> --- a/drivers/gpu/drm/drm_managed.c
> +++ b/drivers/gpu/drm/drm_managed.c
> @@ -139,8 +139,7 @@ void drmm_add_final_kfree(struct drm_device *dev, void *container)
>  {
>  	WARN_ON(dev->managed.final_kfree);
>  	WARN_ON(dev < (struct drm_device *) container);
> -	WARN_ON(dev + 1 >=
> -		(struct drm_device *) (container + ksize(container)));
> +	WARN_ON(dev + 1 > (struct drm_device *) (container + ksize(container)));

I do not think this is the right fix...
The original code would trigger if
1) the container only had a drm_device - and nothing else
2) and the allocated size was the same

And the modification will now allow for a container with the exact size
of drm_device.

I checked all users in my tree - no-one only had a drm_device.
The minimum was one extra pointer.

Another thing that could trigger the warning was if any users
did not specify a pointer to memory allocated by k(z)alloc()
But I could not find any.

tiny/st7735r.c looked suspisius, but I think it is also OK,
because struct st7735r_priv is allocated, but the poitner specified in
st7735r_priv.dbidev. But dbidev is the first field - so OK.

So no better clue...

	Sam
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Re: [PATCH] drm/managed: Fix off-by-one in warning

[Daniel Vetter]

On Sat, Mar 28, 2020 at 7:49 PM Sam Ravnborg <sam@ravnborg.org> wrote:
>
> Hi Daniel.
>
> On Sat, Mar 28, 2020 at 05:23:58PM +0100, Daniel Vetter wrote:
> > I'm thinking this is the warning that fired in the 0day report, but I
> > can't double-check yet since 0day didn't upload its source tree
> > anywhere I can check. And all the drivers I can easily test don't use
> > drm_dev_alloc anymore ...
> >
> > Also if I'm correct supreme amounts of bad luck because usually kslap
> > (for bigger structures) gives us something quite a bit bigger than
> > what we asked for.
> >
> > Reported-by: kernel test robot <lkp@intel.com>
> > Fixes: c6603c740e0e ("drm: add managed resources tied to drm_device")
> > Cc: Sam Ravnborg <sam@ravnborg.org>
> > Cc: Thomas Zimmermann <tzimmermann@suse.de>
> > Cc: Dan Carpenter <dan.carpenter@oracle.com>
> > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > Cc: Neil Armstrong <narmstrong@baylibre.com
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > ---
> >  drivers/gpu/drm/drm_managed.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
> > index 4955241ceb4c..9cebfe370a65 100644
> > --- a/drivers/gpu/drm/drm_managed.c
> > +++ b/drivers/gpu/drm/drm_managed.c
> > @@ -139,8 +139,7 @@ void drmm_add_final_kfree(struct drm_device *dev, void *container)
> >  {
> >       WARN_ON(dev->managed.final_kfree);
> >       WARN_ON(dev < (struct drm_device *) container);
> > -     WARN_ON(dev + 1 >=
> > -             (struct drm_device *) (container + ksize(container)));
> > +     WARN_ON(dev + 1 > (struct drm_device *) (container + ksize(container)));
>
> I do not think this is the right fix...
> The original code would trigger if
> 1) the container only had a drm_device - and nothing else
> 2) and the allocated size was the same

Yup, which apparently happens for all the drivers calling
drm_dev_alloc(). At least on the unlucky architecture that 0day tested
on (or build settings, or whatever). The issue was hit with drm/bochs,
which is still using drm_dev_alloc (like most older-ish drivers).

> And the modification will now allow for a container with the exact size
> of drm_device.
>
> I checked all users in my tree - no-one only had a drm_device.
> The minimum was one extra pointer.
>
> Another thing that could trigger the warning was if any users
> did not specify a pointer to memory allocated by k(z)alloc()
> But I could not find any.
>
> tiny/st7735r.c looked suspisius, but I think it is also OK,
> because struct st7735r_priv is allocated, but the poitner specified in
> st7735r_priv.dbidev. But dbidev is the first field - so OK.
>
> So no better clue...

Yeah all the drivers using drm_dev_init with embedded drm_device wont hit this.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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Re: [PATCH] drm/managed: Fix off-by-one in warning

[Sam Ravnborg]

On Sat, Mar 28, 2020 at 11:02:26PM +0100, Daniel Vetter wrote:
> On Sat, Mar 28, 2020 at 7:49 PM Sam Ravnborg <sam@ravnborg.org> wrote:
> >
> > Hi Daniel.
> >
> > On Sat, Mar 28, 2020 at 05:23:58PM +0100, Daniel Vetter wrote:
> > > I'm thinking this is the warning that fired in the 0day report, but I
> > > can't double-check yet since 0day didn't upload its source tree
> > > anywhere I can check. And all the drivers I can easily test don't use
> > > drm_dev_alloc anymore ...
> > >
> > > Also if I'm correct supreme amounts of bad luck because usually kslap
> > > (for bigger structures) gives us something quite a bit bigger than
> > > what we asked for.
> > >
> > > Reported-by: kernel test robot <lkp@intel.com>
> > > Fixes: c6603c740e0e ("drm: add managed resources tied to drm_device")
> > > Cc: Sam Ravnborg <sam@ravnborg.org>
> > > Cc: Thomas Zimmermann <tzimmermann@suse.de>
> > > Cc: Dan Carpenter <dan.carpenter@oracle.com>
> > > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > Cc: Neil Armstrong <narmstrong@baylibre.com
> > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > > ---
> > >  drivers/gpu/drm/drm_managed.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
> > > index 4955241ceb4c..9cebfe370a65 100644
> > > --- a/drivers/gpu/drm/drm_managed.c
> > > +++ b/drivers/gpu/drm/drm_managed.c
> > > @@ -139,8 +139,7 @@ void drmm_add_final_kfree(struct drm_device *dev, void *container)
> > >  {
> > >       WARN_ON(dev->managed.final_kfree);
> > >       WARN_ON(dev < (struct drm_device *) container);
> > > -     WARN_ON(dev + 1 >=
> > > -             (struct drm_device *) (container + ksize(container)));
> > > +     WARN_ON(dev + 1 > (struct drm_device *) (container + ksize(container)));
> >
> > I do not think this is the right fix...
> > The original code would trigger if
> > 1) the container only had a drm_device - and nothing else
> > 2) and the allocated size was the same
> 
> Yup, which apparently happens for all the drivers calling
> drm_dev_alloc(). At least on the unlucky architecture that 0day tested
> on (or build settings, or whatever). The issue was hit with drm/bochs,
> which is still using drm_dev_alloc (like most older-ish drivers).

That explains it and then the checks makes sense.

Reviewed-by: Sam Ravnborg <sam@ravnborg.org>


	Sam
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Re: [PATCH] drm/managed: Fix off-by-one in warning

[Daniel Vetter]

On Mon, Mar 30, 2020 at 12:29:44PM +0200, Sam Ravnborg wrote:
> On Sat, Mar 28, 2020 at 11:02:26PM +0100, Daniel Vetter wrote:
> > On Sat, Mar 28, 2020 at 7:49 PM Sam Ravnborg <sam@ravnborg.org> wrote:
> > >
> > > Hi Daniel.
> > >
> > > On Sat, Mar 28, 2020 at 05:23:58PM +0100, Daniel Vetter wrote:
> > > > I'm thinking this is the warning that fired in the 0day report, but I
> > > > can't double-check yet since 0day didn't upload its source tree
> > > > anywhere I can check. And all the drivers I can easily test don't use
> > > > drm_dev_alloc anymore ...
> > > >
> > > > Also if I'm correct supreme amounts of bad luck because usually kslap
> > > > (for bigger structures) gives us something quite a bit bigger than
> > > > what we asked for.
> > > >
> > > > Reported-by: kernel test robot <lkp@intel.com>
> > > > Fixes: c6603c740e0e ("drm: add managed resources tied to drm_device")
> > > > Cc: Sam Ravnborg <sam@ravnborg.org>
> > > > Cc: Thomas Zimmermann <tzimmermann@suse.de>
> > > > Cc: Dan Carpenter <dan.carpenter@oracle.com>
> > > > Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > > Cc: Neil Armstrong <narmstrong@baylibre.com
> > > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > > > ---
> > > >  drivers/gpu/drm/drm_managed.c | 3 +--
> > > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
> > > > index 4955241ceb4c..9cebfe370a65 100644
> > > > --- a/drivers/gpu/drm/drm_managed.c
> > > > +++ b/drivers/gpu/drm/drm_managed.c
> > > > @@ -139,8 +139,7 @@ void drmm_add_final_kfree(struct drm_device *dev, void *container)
> > > >  {
> > > >       WARN_ON(dev->managed.final_kfree);
> > > >       WARN_ON(dev < (struct drm_device *) container);
> > > > -     WARN_ON(dev + 1 >=
> > > > -             (struct drm_device *) (container + ksize(container)));
> > > > +     WARN_ON(dev + 1 > (struct drm_device *) (container + ksize(container)));
> > >
> > > I do not think this is the right fix...
> > > The original code would trigger if
> > > 1) the container only had a drm_device - and nothing else
> > > 2) and the allocated size was the same
> > 
> > Yup, which apparently happens for all the drivers calling
> > drm_dev_alloc(). At least on the unlucky architecture that 0day tested
> > on (or build settings, or whatever). The issue was hit with drm/bochs,
> > which is still using drm_dev_alloc (like most older-ish drivers).
> 
> That explains it and then the checks makes sense.
> 
> Reviewed-by: Sam Ravnborg <sam@ravnborg.org>

Thanks for your review, patch applied and a note to the commit message
added that 0day confirmed that it's indeed this WARN_ON that they've hit.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH] drm/managed: Fix off-by-one in warning

[Daniel Vetter]

Ok 0day people uploaded the tree they tested (from patches) now, I
confirmed it's indeed this line that's blowing up.
-Daniel

On Sat, Mar 28, 2020 at 5:24 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
> I'm thinking this is the warning that fired in the 0day report, but I
> can't double-check yet since 0day didn't upload its source tree
> anywhere I can check. And all the drivers I can easily test don't use
> drm_dev_alloc anymore ...
>
> Also if I'm correct supreme amounts of bad luck because usually kslap
> (for bigger structures) gives us something quite a bit bigger than
> what we asked for.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Fixes: c6603c740e0e ("drm: add managed resources tied to drm_device")
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Cc: Neil Armstrong <narmstrong@baylibre.com
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_managed.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_managed.c b/drivers/gpu/drm/drm_managed.c
> index 4955241ceb4c..9cebfe370a65 100644
> --- a/drivers/gpu/drm/drm_managed.c
> +++ b/drivers/gpu/drm/drm_managed.c
> @@ -139,8 +139,7 @@ void drmm_add_final_kfree(struct drm_device *dev, void *container)
>  {
>         WARN_ON(dev->managed.final_kfree);
>         WARN_ON(dev < (struct drm_device *) container);
> -       WARN_ON(dev + 1 >=
> -               (struct drm_device *) (container + ksize(container)));
> +       WARN_ON(dev + 1 > (struct drm_device *) (container + ksize(container)));
>         dev->managed.final_kfree = container;
>  }
>  EXPORT_SYMBOL(drmm_add_final_kfree);
> --
> 2.25.1
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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