CVE-2026-89650

Description

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.

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Patch details

Severity score breakdown

CVSS version: CVSS v3.0

References

• MITRE
• NVD
• Launchpad
• Debian

Related Ubuntu Security Notices (USN)

• USN-8961-1
• Linux kernel vulnerabilities
• 3 November 2026
• USN-8962-1
• Linux kernel (Azure CVM) vulnerabilities
• 3 November 2026
• USN-8959-1
• Linux kernel vulnerabilities
• 3 November 2026
• USN-8963-1
• Linux kernel (NVIDIA Tegra) vulnerabilities
• 3 November 2026
• USN-8960-1
• Linux kernel (OEM) vulnerabilities
• 3 November 2026
• USN-9002-1
• Linux kernel (NVIDIA Tegra) vulnerabilities
• 6 November 2026

Other references

• https://www.cve.org/CVERecord?id=CVE-2026-89650
• https://git.kernel.org/linus/a3eb169ee297aa99670ba927c659990bd1e453f3 (7.3-rc1)
• https://git.kernel.org/stable/c/332c444f4dc6fa1e8b8637c9e82d29e97f768656
• https://git.kernel.org/stable/c/3bf7dba8dba9a05774b846affec61a3624ddba38
• https://git.kernel.org/stable/c/58c2d3e954c13694ef6e820a5e9456461bb9e7df
• https://git.kernel.org/stable/c/a3eb169ee297aa99670ba927c659990bd1e453f3