drm/vc4: Shut down BO cache timer before teardown

Overview

In the Linux kernel, the following vulnerability has been resolved:

drm/vc4: Shut down BO cache timer before teardown

The BO cache timer callback schedules time_work, and time_work can rearm the timer through vc4_bo_cache_free_old().

vc4_bo_cache_destroy() deletes the timer and then cancels the work, which does not break that cycle: the work being cancelled can rearm the timer, and the timer then queues work again after teardown.

Use timer_shutdown_sync() instead, so the timer cannot be rearmed and the cycle ends with cancel_work_sync().

Affected

• Linux >= c826a6e1064419f78855463cf29ce9e8b9d25bf4 < cf55c6f1b62a89bf365c48bf731ccf69340e3a16
• Linux >= c826a6e1064419f78855463cf29ce9e8b9d25bf4 < e9264ee59bd94970b80b7548f693bccf0d4628da
• Linux >= c826a6e1064419f78855463cf29ce9e8b9d25bf4 < a38f2724eb93a78ba250b01e0caf3468df4d3956
• Linux >= c826a6e1064419f78855463cf29ce9e8b9d25bf4 < bac4c1a9af690b8635c6924872075c41d8763ed9
• Linux >= c826a6e1064419f78855463cf29ce9e8b9d25bf4 < 6273dd3ffb54ec581855b82ae77331b66028249c
• Linux 4.5

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.