CVE-2026-43405: libceph: Use u32 for non-negative values in ceph_monmap_decode()

CVE-2026-43405: libceph: Use u32 for non-negative values in ceph_monmap_decode()

[Greg Kroah-Hartman]

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

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

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

libceph: Use u32 for non-negative values in ceph_monmap_decode()

This patch fixes unnecessary implicit conversions that change signedness
of blob_len and num_mon in ceph_monmap_decode().
Currently blob_len and num_mon are (signed) int variables. They are used
to hold values that are always non-negative and get assigned in
ceph_decode_32_safe(), which is meant to assign u32 values. Both
variables are subsequently used as unsigned values, and the value of
num_mon is further assigned to monmap->num_mon, which is of type u32.
Therefore, both variables should be of type u32. This is especially
relevant for num_mon. If the value read from the incoming message is
very large, it is interpreted as a negative value, and the check for
num_mon > CEPH_MAX_MON does not catch it. This leads to the attempt to
allocate a very large chunk of memory for monmap, which will most likely
fail. In this case, an unnecessary attempt to allocate memory is
performed, and -ENOMEM is returned instead of -EINVAL.

The Linux kernel CVE team has assigned CVE-2026-43405 to this issue.


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

	Fixed in 5.15.203 with commit ee5588e2bc41acb73f6676c0520420c107cd0140
	Fixed in 6.1.167 with commit 86f7060cd638d6eb042e8ed780fb83a59ca0dcb3
	Fixed in 6.6.130 with commit 5f2806684b05bd24d05c091083b8e2517ba8ffac
	Fixed in 6.12.78 with commit b268984ae88cb0dcd7a8e8263962c748448e26e8
	Fixed in 6.18.19 with commit ba0a4df8c563536857dcbf7b4dbd0f2a15f57ace
	Fixed in 6.19.9 with commit 08bc6173fd611ad5a40f472bf5f15b92aea0fe40
	Fixed in 7.0 with commit 770444611f047dbfd4517ec0bc1b179d40c2f346

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-2026-43405
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/mon_client.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/ee5588e2bc41acb73f6676c0520420c107cd0140
	https://git.kernel.org/stable/c/86f7060cd638d6eb042e8ed780fb83a59ca0dcb3
	https://git.kernel.org/stable/c/5f2806684b05bd24d05c091083b8e2517ba8ffac
	https://git.kernel.org/stable/c/b268984ae88cb0dcd7a8e8263962c748448e26e8
	https://git.kernel.org/stable/c/ba0a4df8c563536857dcbf7b4dbd0f2a15f57ace
	https://git.kernel.org/stable/c/08bc6173fd611ad5a40f472bf5f15b92aea0fe40
	https://git.kernel.org/stable/c/770444611f047dbfd4517ec0bc1b179d40c2f346