CVE-2026-64439: crypto: krb5 - filter out async aead implementations at alloc

From: Greg Kroah-Hartman <[email protected]>

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

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

crypto: krb5 - filter out async aead implementations at alloc

krb5_aead_encrypt(), krb5_aead_decrypt() in rfc3961_simplified.c and
rfc8009_encrypt(), rfc8009_decrypt() in rfc8009_aes2.c set a NULL
completion callback and treat any negative return from
crypto_aead_{encrypt,decrypt}() as terminal, falling through to
kfree_sensitive(buffer).  When the encrypt_name resolves to an
async AEAD instance the request returns -EINPROGRESS, the buffer
is freed while the backend's worker still holds a pointer, and the
worker dereferences the freed slab on completion.

KASAN report under UML+SLUB with a synthetic async aead backend
bound to krb5->encrypt_name:

  BUG: KASAN: slab-use-after-free in t5_stub_complete+0x7d/0xc7

The helpers were written synchronously, so filter the async
instances out at allocation time instead of plumbing
crypto_wait_req() through every call site.

Reachable via net/rxrpc/rxgk.c, fs/afs/cm_security.c and
net/ceph/crypto.c on systems with an async AEAD provider bound to
the krb5 enctype name.

The Linux kernel CVE team has assigned CVE-2026-64439 to this issue.


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

	Issue introduced in 6.15 with commit 00244da40f7821b242c4612428d4192230dba27f and fixed in 6.18.39 with commit ef6feb77e2d91761427c5b773edc9c97e1b706ad
	Issue introduced in 6.15 with commit 00244da40f7821b242c4612428d4192230dba27f and fixed in 7.1.4 with commit 2b7bd6dccff14b8b632c5244f1fd506918077221
	Issue introduced in 6.15 with commit 00244da40f7821b242c4612428d4192230dba27f and fixed in 7.2-rc1 with commit 6c9dddeb582fde005360f4fe02c760d45ca05fb5

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-2026-64439
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:
	crypto/krb5/krb5_api.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/ef6feb77e2d91761427c5b773edc9c97e1b706ad
	https://git.kernel.org/stable/c/2b7bd6dccff14b8b632c5244f1fd506918077221
	https://git.kernel.org/stable/c/6c9dddeb582fde005360f4fe02c760d45ca05fb5