CVE-2026-64057

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

afs: Fix the locking used by afs_get_link()

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 afs_read_single() to prevent races

between multiple ->get_link() 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 validate_lock around afs_read_single() to prevent races

between multiple ->get_link() calls.

(2) Keep a separate copy of the symlink contents with an rcu_head. 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 folio_queue).

(5) If there's no cache, discard the I/O buffer immediately after reading

and copying if there is no cache.