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.

A flaw was found in libceph within the Linux kernel. This vulnerability allows a local attacker to craft a malformed CRUSH map, which is used for data placement. By doing so, one data bucket can be made to reuse another bucket's memory workspace, leading to an out-of-bounds write. This memory corruption could result in a denial of service or potentially lead to privilege escalation.

Red Hat Enterprise Linux 10 Affected kernel Red Hat Enterprise Linux 10 Affected kernel-rt Red Hat Enterprise Linux 6 Not affected kernel Red Hat Enterprise Linux 7 Affected kernel Red Hat Enterprise Linux 7 Affected kernel-rt Red Hat Enterprise Linux 8 Affected kernel Red Hat Enterprise Linux 8 Affected kernel-rt Red Hat Enterprise Linux 9 Affected kernel Red Hat Enterprise Linux 9 Affected kernel-rt Red Hat OpenShift Container Platform 4 Affected openshift/ose-rhel-coreos-8 Red Hat OpenShift Container Platform 4 Affected openshift/ose-rhel-coreos-9 https://www.cve.org/CVERecord?id=CVE-2026-89656 https://nvd.nist.gov/vuln/detail/CVE-2026-89656 https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89656.mbox