linux-kernel - Re: [PATCH] drm/radeon: fix copy of uninitialized variable back to userspace

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Date:   Thu, 11 Mar 2021 14:10:16 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Christian König <christian.koenig@....com>
Cc:     Colin King <colin.king@...onical.com>,
        Alex Deucher <alexander.deucher@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Marek Olšák <marek.olsak@....com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/radeon: fix copy of uninitialized variable back to
 userspace

On Wed, Mar 03, 2021 at 08:42:31AM +0100, Christian König wrote:
> Am 03.03.21 um 01:27 schrieb Colin King:
> > From: Colin Ian King <colin.king@...onical.com>
> > 
> > Currently the ioctl command RADEON_INFO_SI_BACKEND_ENABLED_MASK can
> > copy back uninitialised data in value_tmp that pointer *value points
> > to. This can occur when rdev->family is less than CHIP_BONAIRE and
> > less than CHIP_TAHITI.  Fix this by adding in a missing -EINVAL
> > so that no invalid value is copied back to userspace.
> > 
> > Addresses-Coverity: ("Uninitialized scalar variable)
> > Cc: stable@...r.kernel.org # 3.13+
> > Fixes: 439a1cfffe2c ("drm/radeon: expose render backend mask to the userspace")
> > Signed-off-by: Colin Ian King <colin.king@...onical.com>
> 
> Reviewed-by: Christian König <christian.koenig@....com>
> 
> Let's hope that this doesn't break UAPI.

If it does I think the only difference would be errno userspace sees
(aside from the stack garbage, which we could also emulate). Switching to
return 0; is easy. So no worries this would be a problem :-)
-Daniel

> 
> Christian.
> 
> > ---
> >   drivers/gpu/drm/radeon/radeon_kms.c | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/gpu/drm/radeon/radeon_kms.c b/drivers/gpu/drm/radeon/radeon_kms.c
> > index 2479d6ab7a36..58876bb4ef2a 100644
> > --- a/drivers/gpu/drm/radeon/radeon_kms.c
> > +++ b/drivers/gpu/drm/radeon/radeon_kms.c
> > @@ -518,6 +518,7 @@ int radeon_info_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
> >   			*value = rdev->config.si.backend_enable_mask;
> >   		} else {
> >   			DRM_DEBUG_KMS("BACKEND_ENABLED_MASK is si+ only!\n");
> > +			return -EINVAL;
> >   		}
> >   		break;
> >   	case RADEON_INFO_MAX_SCLK:
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch