DEBIAN-CVE-2026-68160

In the Linux kernel, the following vulnerability has been resolved:  ceph: fix pre-auth out-of-bounds read on snaptrace in cephhandlecaps()  cephhandlecaps() reads snaptracelen from the wire-format cephmdscaps header and uses it unconditionally to build a fake end pointer (snaptrace + snaptracelen) that is later handed to cephupdatesnaptrace() in the CEPHCAPOPIMPORT case:      snaptrace     = h + 1;     snaptracelen = le32tocpu(h->snaptracelen);     p             = snaptrace + snaptracelen;     ...     case CEPHCAPOPIMPORT:         if (snaptracelen) {             ...             if (cephupdatesnaptrace(mdsc, snaptrace,                                        snaptrace + snaptracelen,                                        false, &realm)) { ... }  cephupdatesnaptrace() then decodes a struct cephmdssnaprealm from snaptrace using cephdecodeneed(&p, e, sizeof(*ri), bad) with the attacker-supplied fake end e == snaptrace + snaptracelen. With snaptracelen == 0xFFFFFFFF the bound check is trivially satisfied, ri = p reads sizeof(struct cephmdssnaprealm) past the legitimate msg->front buffer, and ri->numsnaps / ri->numpriorparentsnaps then drive further out-of-bounds reads of the encoded snap arrays.  The eleven msgversion >= 2 .. msgversion >= 12 decoder blocks above the op switch each catch this OOB through their cephdecode*safe() / cephdecodeneed() helpers, but they sit behind a hdr.version-gated if, so a malicious or compromised MDS that sets msg->hdr.version = 1 reaches the IMPORT path with no version-gated decoder having validated snaptracelen. The shape has been present since cephhandlecaps() was introduced.  Validate snaptracelen against the message front buffer before consuming it, using the canonical cephdecodeneed() / cephhasroom() helper.  The helper bounds the length with subtraction (n <= end - p, guarded by end >= p) rather than pointer addition, so it is wrap-safe for the attacker-controlled u32 length on 32-bit builds where p + snaptracelen could overflow the address space.  This matches the rest of the ceph decode path (e.g. the poolns_len check a few lines below), and the existing goto bad cleanup already covers this exit path.