In the Linux kernel, the following vulnerability has been resolved:
drm/exynos: vidi: use ctx->lock to protect struct vidi_context member variables related to memory alloc/free
Exynos Virtual Display driver performs memory alloc/free operations
without lock protection, which easily causes concurrency problem.
For example, use-after-free can occur in race scenario like this:
```
CPU0 CPU1 CPU2
---- ---- ----
vidi_connection_ioctl()
if (vidi->connection) // true
drm_edid = drm_edid_alloc(); // alloc drm_edid
...
ctx->raw_edid = drm_edid;
...
drm_mode_getconnector()
drm_helper_probe_single_connector_modes()
vidi_get_modes()
if (ctx->raw_edid) // true
drm_edid_dup(ctx->raw_edid);
if (!drm_edid) // false
...
vidi_connection_ioctl()
if (vidi->connection) // false
drm_edid_free(ctx->raw_edid); // free drm_edid
...
drm_edid_alloc(drm_edid->edid)
kmemdup(edid); // UAF!!
...
```
To prevent these vulns, at least in vidi_context, member variables related
to memory alloc/free should be protected with ctx->lock.