On 2020-07-27 16:11, daniel@xxxxxxxx wrote:
On Mon, Jul 27, 2020 at 09:55:07PM +0200, Greg KH wrote:
On Mon, Jul 20, 2020 at 06:30:50PM -0400, Steve Cohen wrote:
> A use-after-free in drm_gem_open_ioctl can happen if the
> GEM object handle is closed between the idr lookup and
> retrieving the size from said object since a local reference
> is not being held at that point. Hold the local reference
> while the object can still be accessed to fix this and
> plug the potential security hole.
>
> Signed-off-by: Steve Cohen <cohens@xxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_gem.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 7bf628e..ee2058a 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -871,9 +871,6 @@ drm_gem_flink_ioctl(struct drm_device *dev, void *data,
> * @file_priv: drm file-private structure
> *
> * Open an object using the global name, returning a handle and the size.
> - *
> - * This handle (of course) holds a reference to the object, so the object
> - * will not go away until the handle is deleted.
> */
> int
> drm_gem_open_ioctl(struct drm_device *dev, void *data,
> @@ -898,14 +895,15 @@ drm_gem_open_ioctl(struct drm_device *dev, void *data,
>
> /* drm_gem_handle_create_tail unlocks dev->object_name_lock. */
> ret = drm_gem_handle_create_tail(file_priv, obj, &handle);
> - drm_gem_object_put_unlocked(obj);
> if (ret)
> - return ret;
> + goto err;
>
> args->handle = handle;
> args->size = obj->size;
>
> - return 0;
> +err:
> + drm_gem_object_put_unlocked(obj);
> + return ret;
> }
>
> /**
As this seems to fix an important issue, any reason it wasn't cc:
stable
on it so that it gets backported properly?
How about a "Fixes:" tag so that we know what commit id it fixes so we
know how far back to backport things?
And a hint to the maintainers that "this is an issue that needs to get
into 5.8-final, it shouldn't wait around longer please" would have
also
been nice to see :)
And what chagned from v1, aren't you supposed to list that somewhere
in
the changelog or below the --- line (never remember what DRM drivers
want here...)
Care to send a v3?
Don't worry, I'm pushing this to drm-misc-fixes now, should still make
it
to 5.8. Plus cc: stable. I didn't bother with Fixes: since I think the
bug
is rather old. Also, worst case you leak 32bit of some kernel memory
that
got reused already (but yeah I know that's often enough to get the foot
in
somewhere nasty and crack the door open).
I think it fell through cracks because Sam said he'll apply, guess that
didn't happen.
Sam added his Reviewed-By on V1 with a comment to rename the goto label,
but in V2 I also updated the API documentation and the commit text for
a more complete change and thought he would re-add the tag.
Also yes a changelog, somewhere, for next time around.
Apologies, it won't happen again. Should I still submit a V3?
It looks like you've got Greg's concerns covered.
-Steve
-Daniel
thanks,
greg k-h
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