Currently `struct drm_buf_desc` is defined as follows:

struct drm_buf_desc {
        int count;
        int size;
        int low_mark;
        int high_mark;
        enum {
                _DRM_PAGE_ALIGN = 0x01,
                _DRM_AGP_BUFFER = 0x02,
                _DRM_SG_BUFFER = 0x04,
                _DRM_FB_BUFFER = 0x08,
                _DRM_PCI_BUFFER_RO = 0x10
        } flags;
        unsigned long agp_start;
};

copy_one_buf() is potentially copying uninitialized kernel stack memory
to userspace, since the compiler may leave such "holes" (around `.flags`
and `.agp_start` fields) in this statically allocated structure. Prevent
it by initializing `v` with memset().

Cc: sta...@vger.kernel.org
Fixes: 5c7640ab6258 ("switch compat_drm_infobufs() to drm_ioctl_kernel()")
Suggested-by: Dan Carpenter <dan.carpen...@oracle.com>
Acked-by: Arnd Bergmann <a...@arndb.de>
Signed-off-by: Peilin Ye <yepeilin...@gmail.com>
---
Change in v2:
    - Improve commit description. (Suggested by Arnd Bergmann
      <a...@arndb.de>)

 drivers/gpu/drm/drm_bufs.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_bufs.c b/drivers/gpu/drm/drm_bufs.c
index a0735fbc144b..f99cd4a3f951 100644
--- a/drivers/gpu/drm/drm_bufs.c
+++ b/drivers/gpu/drm/drm_bufs.c
@@ -1349,10 +1349,14 @@ static int copy_one_buf(void *data, int count, struct 
drm_buf_entry *from)
 {
        struct drm_buf_info *request = data;
        struct drm_buf_desc __user *to = &request->list[count];
-       struct drm_buf_desc v = {.count = from->buf_count,
-                                .size = from->buf_size,
-                                .low_mark = from->low_mark,
-                                .high_mark = from->high_mark};
+       struct drm_buf_desc v;
+
+       memset(&v, 0, sizeof(v));
+
+       v.count = from->buf_count;
+       v.size = from->buf_size;
+       v.low_mark = from->low_mark;
+       v.high_mark = from->high_mark;
 
        if (copy_to_user(to, &v, offsetof(struct drm_buf_desc, flags)))
                return -EFAULT;
-- 
2.25.1

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