[PATCH] drm: Prevent overwriting from userspace underallocating core ioctl structs

[Chris Wilson]

Apply the protections from

commit 1b2f1489633888d4a06028315dc19d65768a1c05
Author: Dave Airlie <airlied at redhat.com>
Date:   Sat Aug 14 20:20:34 2010 +1000

    drm: block userspace under allocating buffer and having drivers overwrite it (v2)

to the core ioctl structs as well, for we found one instance where there
is a 32-/64-bit size mismatch and were guilty of writing beyond the end
of the user's buffer.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Dave Airlie <airlied at redhat.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: dri-devel at lists.freedesktop.org
Cc: stable at vger.kernel.org
---
 drivers/gpu/drm/drm_drv.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index e572dd20bdee..05ad9ba0a67e 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -402,9 +402,16 @@ long drm_ioctl(struct file *filp,
 		cmd = ioctl->cmd_drv;
 	}
 	else if ((nr >= DRM_COMMAND_END) || (nr < DRM_COMMAND_BASE)) {
+		u32 drv_size;
+
 		ioctl = &drm_ioctls[nr];
-		cmd = ioctl->cmd;
+
+		drv_size = _IOC_SIZE(ioctl->cmd);
 		usize = asize = _IOC_SIZE(cmd);
+		if (drv_size > asize)
+			asize = drv_size;
+
+		cmd = ioctl->cmd;
 	} else
 		goto err_i1;
 
-- 
1.8.4.rc3