CVE-2026-64057: afs: Fix the locking used by afs_get_link()
In the Linux kernel, the following vulnerability has been resolved:
afs: Fix the locking used by afsgetlink()
The afs filesystem in the kernel doesn't do locking correctly for symbolic links. There are a number of problems:
(1) It doesn't do any locking around afsreadsingle() to prevent races between multiple ->getlink() calls, thereby allowing the possibility of leaks.
(2) It doesn't use RCU barriering when accessing the buffer pointers during RCU pathwalk.
(3) It can race with another thread updating the contents of the symlink if a third party updated it on the server.
Fix this by the following means:
(0) Move symlink handling into its own file as this makes it more complicated.
(1) Take the validatelock around afsreadsingle() to prevent races between multiple ->getlink() calls.
(2) Keep a separate copy of the symlink contents with an rcuhead. This is always going to be a lot smaller than a page, so it can be kmalloc'd and save quite a bit of memory. It also needs a refcount for non-RCU pathwalk.
(3) Split the symlink read and write-to-cache routines in afs from those for directories.
(4) Discard the I/O buffer as soon as the write-to-cache completes as this is a full page (plus a folioqueue).
(5) If there's no cache, discard the I/O buffer immediately after reading and copying if there is no cache.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Compensating control
Take validate_lock around afs_read_single() to prevent races between concurrent symlink reads.
- Compensating control
Keep a separate copy of the symlink contents with an rcu_head, and use RCU barriering when accessing the buffer pointers.
- Compensating control
Add a refcount for the symlink contents and split the afs symlink read and write-to-cache routines to prevent races with updates.
- Compensating control
Discard the I/O buffer as soon as write-to-cache completes; when no cache is present, discard the I/O buffer immediately after reading.
- Compensating control
Move symlink handling into its own file.
Event History
Frequently Asked Questions
What access does an attacker need to exploit this issue?
The CVSS vector indicates local access and low privileges are required. No user interaction is required.
Which systems are realistically exposed?
Systems using the Linux kernel AFS filesystem are exposed, particularly where symbolic links in AFS may be accessed concurrently or updated by a third party on the server.
What is the impact of successful exploitation?
The vulnerability is rated high severity with impacts to confidentiality, integrity, and availability all rated High. The described races can allow memory leaks and unsafe handling of symlink contents.
What should be done if the system is affected?
Apply the available Linux kernel patch. The provided stable kernel references identify patches associated with the fix.