[PATCH AUTOSEL 4.19 005/671] drm/virtio: fix bounds check in virtio_gpu_cmd_get_capset()

[Sasha Levin]

From: Dan Carpenter <dan.carpenter at oracle.com>

[ Upstream commit 09c4b49457434fa74749ad6194ef28464d9f5df9 ]

This doesn't affect runtime because in the current code "idx" is always
valid.

First, we read from "vgdev->capsets[idx].max_size" before checking
whether "idx" is within bounds.  And secondly the bounds check is off by
one so we could end up reading one element beyond the end of the
vgdev->capsets[] array.

Fixes: 62fb7a5e1096 ("virtio-gpu: add 3d/virgl support")
Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20180704094250.m7sgvvzg3dhcvv3h@kili.mountain
Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/gpu/drm/virtio/virtgpu_vq.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c
index c8a581b1f4c4..608906f06ced 100644
--- a/drivers/gpu/drm/virtio/virtgpu_vq.c
+++ b/drivers/gpu/drm/virtio/virtgpu_vq.c
@@ -650,11 +650,11 @@ int virtio_gpu_cmd_get_capset(struct virtio_gpu_device *vgdev,
 {
 	struct virtio_gpu_get_capset *cmd_p;
 	struct virtio_gpu_vbuffer *vbuf;
-	int max_size = vgdev->capsets[idx].max_size;
+	int max_size;
 	struct virtio_gpu_drv_cap_cache *cache_ent;
 	void *resp_buf;
 
-	if (idx > vgdev->num_capsets)
+	if (idx >= vgdev->num_capsets)
 		return -EINVAL;
 
 	if (version > vgdev->capsets[idx].max_version)
@@ -664,6 +664,7 @@ int virtio_gpu_cmd_get_capset(struct virtio_gpu_device *vgdev,
 	if (!cache_ent)
 		return -ENOMEM;
 
+	max_size = vgdev->capsets[idx].max_size;
 	cache_ent->caps_cache = kmalloc(max_size, GFP_KERNEL);
 	if (!cache_ent->caps_cache) {
 		kfree(cache_ent);
-- 
2.20.1