afs: Fix the locking used by afs_get_link()

Summary

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.

Timeline

1. Jul 19, 2026, 3:39 PM UTCCVE published
2. Oct 15, 2026, 10:07 AM UTCRecord last updated

Affected versions

• Linux Linux

  From eae9e78951bb02a7b94a9adef6e981413d13c564 · fixed in 93531bca46707c6c28c4f4eb26c101fa36ccb8cb; From eae9e78951bb02a7b94a9adef6e981413d13c564 · fixed in 77ea917cbed62882a33114b1e23ededb977e4287; From eae9e78951bb02a7b94a9adef6e981413d13c564 · fixed in c0410adf3da6db46f3513411fcf95e63c2f1d1ad

• Linux Linux

  6.14

• KernelLinux

  From 6.14.0 · fixed in 6.18.57; From 6.19.0 · fixed in 7.0.11

References 3