of/overlay: only treat a positive changeset id as registered

Overview

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

of/overlay: only treat a positive changeset id as registered

of_overlay_fdt_apply() stores the idr_alloc() return value in ovcs->id before checking it. On failure the stored id is negative, free_overlay_changeset()'s "if (ovcs->id)" check passes, idr_remove() is called with a negative id and list_del() runs on ovcs->ovcs_list, which is not initialized until after the id allocation. An allocation failure at that point dereferences NULL.

Make free_overlay_changeset() treat only a strict-positive id as registered. The rest of the function already copes with a partially-initialized ovcs, so the error path stays a plain goto err_free_ovcs.

Affected

• Linux >= 61b4de4e0b384f4a22c55c3bada604da49cec4e1 < c08a54df9d33dcd6ff089adc9434b2c008af3a39
• Linux >= 61b4de4e0b384f4a22c55c3bada604da49cec4e1 < 0d1525fdcd3355672b7485d61e55df6824ab5ad1
• Linux >= 61b4de4e0b384f4a22c55c3bada604da49cec4e1 < c875407c34dadaef0599834ad9c815f4c9f50d15
• Linux >= 61b4de4e0b384f4a22c55c3bada604da49cec4e1 < 44081d708b5b885487bac792db78324b7b4c267d
• Linux 4.15

Remediation

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