DEBIAN-CVE-2026-89650

In the Linux kernel, the following vulnerability has been resolved:  ceph: bound numexporttargets array for mds info v2/v3  cephmdsmapdecode() in fs/ceph/mdsmap.c reads numexporttargets from each per-mds info record and advances the decode cursor by numexporttargets  sizeof(u32) without first checking that many bytes remain. The only upper-bound check that catches a runaway cursor (p > infoend) is gated on infov >= 4, because infoend is left NULL for infov 2 and 3. When the monitor sends an MDS map whose per-mds info version is 2 or 3 with an oversized numexporttargets, the cursor moves past the message front buffer and the later export-targets loop calls the unchecked cephdecode32() on out-of-bounds memory.  A kernel client processes CEPHMSGMDSMAP from its monitor session (net/ceph/monclient.c dispatches it; fs/ceph/super.c routes it to cephmdschandlemdsmap(), which sets end to the front buffer bound and calls cephmdsmapdecode()). 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 x8664 with KASAN it is reported as a slab-out-of-bounds read in cephmdsmapdecode(). The decoded values land in the internal info->exporttargets[] 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 numexporttargets field triggers an out-of-bounds read in the CephFS client kernel.  Add a cephdecodeneed() for the export-targets array before advancing the cursor, so the bound is enforced for every infov >= 2, not only infov >= 4. This mirrors the count-then-need idiom already used for mdatapgpools later in the same function.  Compute the export-targets byte count with sizemul() and reuse that checked length when advancing the cursor, so the attacker-controlled numexport_targets multiplication fails closed on overflow rather than relying on the later kcalloc() guard.