CVE-2026-89656: libceph: reject buckets with mismatched CRUSH ids

CVE-2026-89656: libceph: reject buckets with mismatched CRUSH ids

[Greg Kroah-Hartman]

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

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

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

libceph: reject buckets with mismatched CRUSH ids

crush_decode() stores bucket data by array slot, and the mapper later
derives the per-bucket workspace index from the decoded bucket id. A
malformed map can therefore make one bucket reuse another bucket's
workspace by encoding an id different from -1 - slot.

For uniform buckets, the second replica selection expands the source
bucket's permutation into that aliased workspace buffer. If the source
bucket is larger than the aliased bucket, the write runs past the smaller
permutation array and can escape the kvmalloc'd CRUSH workspace. KASAN
reports a slab OOB write of 4 bytes in bucket_perm_choose().

Reject buckets whose encoded id does not match their array slot. Valid
CRUSH maps already use the canonical negative id corresponding to the
bucket slot, so this restores the invariant expected by
work->work[-1 - in->id] without changing valid map behavior.

The Linux kernel CVE team has assigned CVE-2026-89656 to this issue.


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

	Issue introduced in 4.11 with commit 66a0e2d579dbec5c676cfe446234ffebb267c564 and fixed in 6.12.109 with commit 3516a4131c4e45d62ee4e42e82c36930e8c1fbbd
	Issue introduced in 4.11 with commit 66a0e2d579dbec5c676cfe446234ffebb267c564 and fixed in 6.18.50 with commit 00562ccd4e88d092b9b851df50fad20442bfeb24
	Issue introduced in 4.11 with commit 66a0e2d579dbec5c676cfe446234ffebb267c564 and fixed in 7.2.4 with commit 79900d978158b2d80eef952fc41b9e4dc58d7b83
	Issue introduced in 4.11 with commit 66a0e2d579dbec5c676cfe446234ffebb267c564 and fixed in 7.3-rc1 with commit 3cde4a8302301679937474a5f7a851394cc1bd11

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-2026-89656
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:
	net/ceph/osdmap.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/3516a4131c4e45d62ee4e42e82c36930e8c1fbbd
	https://git.kernel.org/stable/c/00562ccd4e88d092b9b851df50fad20442bfeb24
	https://git.kernel.org/stable/c/79900d978158b2d80eef952fc41b9e4dc58d7b83
	https://git.kernel.org/stable/c/3cde4a8302301679937474a5f7a851394cc1bd11