linux-kernel - [PATCH 1/4] drm/virtio: Ensure cached capset entries are valid before copying.

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Message-Id: <20190605234423.11348-1-davidriley@chromium.org>
Date:   Wed,  5 Jun 2019 16:44:20 -0700
From:   davidriley@...omium.org
To:     dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org
Cc:     David Airlie <airlied@...ux.ie>, Gerd Hoffmann <kraxel@...hat.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-kernel@...r.kernel.org,
        David Riley <davidriley@...omium.org>
Subject: [PATCH 1/4] drm/virtio: Ensure cached capset entries are valid before copying.

From: David Riley <davidriley@...omium.org>

virtio_gpu_get_caps_ioctl could return success with invalid data if a
second caller to the function occurred after the entry was created in
virtio_gpu_cmd_get_capset but prior to the virtio_gpu_cmd_capset_cb
callback being called.  This could leak contents of memory as well
since the caps_cache allocation is done without zeroing.

Signed-off-by: David Riley <davidriley@...omium.org>
---
 drivers/gpu/drm/virtio/virtgpu_ioctl.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
index 949a264985fc..88c1ed57a3c5 100644
--- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
+++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
@@ -526,7 +526,6 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
 	list_for_each_entry(cache_ent, &vgdev->cap_cache, head) {
 		if (cache_ent->id == args->cap_set_id &&
 		    cache_ent->version == args->cap_set_ver) {
-			ptr = cache_ent->caps_cache;
 			spin_unlock(&vgdev->display_info_lock);
 			goto copy_exit;
 		}
@@ -537,6 +536,7 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
 	virtio_gpu_cmd_get_capset(vgdev, found_valid, args->cap_set_ver,
 				  &cache_ent);
 
+copy_exit:
 	ret = wait_event_timeout(vgdev->resp_wq,
 				 atomic_read(&cache_ent->is_valid), 5 * HZ);
 	if (!ret)
@@ -544,7 +544,6 @@ static int virtio_gpu_get_caps_ioctl(struct drm_device *dev,
 
 	ptr = cache_ent->caps_cache;
 
-copy_exit:
 	if (copy_to_user((void __user *)(unsigned long)args->addr, ptr, size))
 		return -EFAULT;
 
-- 
2.22.0.rc1.311.g5d7573a151-goog