CVE-2026-89650

Status: UPDATED  |  Advisory ID: CVE-2026-89650

Key Details

Affected Products, Subsystems & Sectors

What to Know

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

ceph: bound num_export_targets array for mds info v2/v3

ceph_mdsmap_decode() in fs/ceph/mdsmap.c reads num_export_targets from

each per-mds info record and advances the decode cursor by

num_export_targets * sizeof(u32) without first checking that many bytes

remain. The only upper-bound check that catches a runaway cursor

(*p > info_end) is gated on info_v >= 4, because info_end is left NULL

for info_v 2 and 3. When the monitor sends an MDS map whose per-mds

info version is 2 or 3 with an oversized num_export_targets, the cursor

moves past the message front buffer and the later export-targets loop

calls the unchecked ceph_decode_32() on out-of-bounds memory.

A kernel client processes CEPH_MSG_MDS_MAP from its monitor session

(net/ceph/mon_client.c dispatches it; fs/ceph/super.c routes it to

ceph_mdsc_handle_mdsmap(), which sets end to the front buffer bound and

calls ceph_mdsmap_decode()). A malicious or compromised monitor, or an

on-path attacker on an unsigned/unencrypted messenger session, can

therefore drive an out-of-bounds read in the client kernel; on x86_64

with KASAN it is reported as a slab-out-of-bounds read in

ceph_mdsmap_decode(). The decoded values land in the internal

info->export_targets[] array, so the consequence is a kernel

out-of-bounds read, not an information leak to the attacker.

Impact: a malicious or compromised Ceph monitor sending an MDS map with

a per-mds info version of 2 or 3 and an oversized num_export_targets

field triggers an out-of-bounds read in the CephFS client kernel.

Add a ceph_decode_need() for the export-targets array before advancing

the cursor, so the bound is enforced for every info_v >= 2, not only

info_v >= 4. This mirrors the count-then-need idiom already used for

m_data_pg_pools later in the same function.

Compute the export-targets byte count with size_mul() and reuse that

checked length when advancing the cursor, so the attacker-controlled

num_export_targets multiplication fails closed on overflow rather than

relying on the later kcalloc() guard. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References