xfs: fix cursor and pointer handling when recovering iunlink buckets

Overview

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

xfs: fix cursor and pointer handling when recovering iunlink buckets

LOLLM pointed out a bug in xlog_recover_iunlink_bucket:

1. We don't null out prev_ip after releasing it, which can lead to UAF problems if the inodegc flush call in the loop fails.

at which point I noticed even more bugs:

2. If the inodegc flush inside the loop fails, we also leak @ip.

3. We set prev_agino to agino having already advanced agino, which results in inodes with i_prev_unlinked set to itself.

4. If we exit the bottom of the loop with prev_ip set, then prev_ip aliases ip and we also set its i_prev_unlinked to itself.

Bugs 3 and 4 introduce loops into the unlinked list, though these loops don't surface because we immediately flush each unlinked inode after loading it.

Fix all of these issues.

Affected

• Linux >= 04755d2e5821b3afbaadd09fe5df58d04de36484 < 8c9d5b8a96d6b93eb24e07b4163c89341ba29bd1
• Linux >= 04755d2e5821b3afbaadd09fe5df58d04de36484 < 66a2179d02668f8df44b1a249899006f3ba38ea0
• Linux >= 04755d2e5821b3afbaadd09fe5df58d04de36484 < 961c717e6bf0e53c2c2b1fe4aef1add9390fedab
• Linux >= 04755d2e5821b3afbaadd09fe5df58d04de36484 < 65f39d09d73718611cee40399179323b5d4ead00
• Linux 6.0

Remediation

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