of/overlay: don't leak fragment references when changeset init fails

Overview

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

of/overlay: don't leak fragment references when changeset init fails

init_overlay_changeset() stores the number of initialized fragments in ovcs->count only on full success. When find_target() or the symbols lookup fails partway through, the target and overlay references taken for the fragments initialized so far are never dropped: free_overlay_changeset() bounds its cleanup loop by ovcs->count, which is still 0.

Store the running count on the error path so free_overlay_changeset() puts whatever was set up. The store is guarded by ovcs->fragments because on the allocation-failure path cnt still holds the counting pass total while there is no fragments array; everywhere else cnt only counts fully-initialized fragments.

Affected

• Linux >= 61b4de4e0b384f4a22c55c3bada604da49cec4e1 < 894573e2fdaeb1b15030b7eebc22615edf28a6cd
• Linux >= 61b4de4e0b384f4a22c55c3bada604da49cec4e1 < 7a46f1917b320cc8762183b802301da02a191b6a
• Linux >= 61b4de4e0b384f4a22c55c3bada604da49cec4e1 < 3a23fb158ba517b77a2e5258263bdfdaa480f758
• Linux >= 61b4de4e0b384f4a22c55c3bada604da49cec4e1 < 1d62f0f2bc7edb12ed09f71203df0e47fa4efca4
• Linux 4.15

Remediation

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