CVE-2026-97583: afs: Clear stale peer app data after address list changes

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

afs: Clear stale peer app data after address list changes

afs_fs_probe_fileserver() fetches the current endpoint state under
server->fs_lock, but leaves old_alist as NULL.  Consequently,
afs_set_peer_appdata() treats every address list replacement as initial
setup and only binds the new peers; it never unbinds peers removed from
the old list.

An address refresh can therefore proceed as follows.  CPU 0 replaces
server S's list and drops Pold without clearing Pold->app_data.  The
server destroyer then clears only S's current peers and lets S reach its
RCU callback.  After the callback frees S, CPU 1 handles a callback
through an RxRPC connection that still pins Pold, reads Pold->app_data,
and calls afs_use_server() on the freed object.

KASAN reported:

  BUG: KASAN: slab-use-after-free in afs_find_server+0x3c/0xa0
  Read of size 4 at addr ffff8881013e1af0 by task krxrpcio/7001/74
  Call Trace:
   afs_find_server+0x3c/0xa0
   afs_rx_new_call+0x15c/0x390
   rxrpc_new_incoming_call+0x97c/0x1730
   rxrpc_input_packet.constprop.0+0xd03/0xec0
   rxrpc_io_thread+0x967/0x1640
  Allocated by task 93:
   afs_lookup_server+0x1a7/0x14c0
   afs_alloc_server_list+0x43f/0xb60
   afs_create_volume+0x923/0x1490
   afs_get_tree+0x1c6/0x10a0
  Freed by task 0:
   kfree+0x131/0x3c0
   rcu_core+0x50a/0x1850
  Last potentially related work creation:
   __call_rcu_common.constprop.0+0x71/0xa10
   afs_put_server+0x213/0x2b0

Preserve old->addresses for the peer app-data update so that removed
peers are cleared before the endpoint state is replaced.  Also advance
both cursors when the old and new lists share a peer; activating the
old/new comparison without this would otherwise loop forever on the
shared entry.

The Linux kernel CVE team has assigned CVE-2026-97583 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.12.101 with commit 39ba6af83a7f9dee3e6a7916f41a48bcbda54eba and fixed in 6.12.111 with commit 3afb988fd0411707bdafb9b321086fff0da28aae
	Issue introduced in 6.15 with commit 40e8b52fe8c8ab6920ea5f59c5469b6918cce624 and fixed in 6.18.53 with commit c7f77a11a1e719192c7262aad38a3919aec62c21
	Issue introduced in 6.15 with commit 40e8b52fe8c8ab6920ea5f59c5469b6918cce624 and fixed in 7.2.7 with commit 7f7f5589d048821dea316cbac9b37d27eaf7530e
	Issue introduced in 6.15 with commit 40e8b52fe8c8ab6920ea5f59c5469b6918cce624 and fixed in 7.3-rc3 with commit ba0623fc19a424f4745394c499f9f28a8d88d397

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-97583
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/afs/addr_list.c
	fs/afs/fs_probe.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3afb988fd0411707bdafb9b321086fff0da28aae
	https://git.kernel.org/stable/c/c7f77a11a1e719192c7262aad38a3919aec62c21
	https://git.kernel.org/stable/c/7f7f5589d048821dea316cbac9b37d27eaf7530e
	https://git.kernel.org/stable/c/ba0623fc19a424f4745394c499f9f28a8d88d397