Linux Kernel Ceph Cap Handler Reads snap_trace_len from the Wire and Uses It Without Bounds Checking, Enabling a Network-Controlled Out-of-Bounds Read Before Authentication

Status: NEW  |  Advisory ID: CVE-2026-68160

Key Details

What to Know

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

ceph: fix pre-auth out-of-bounds read on snaptrace in ceph_handle_caps()

ceph_handle_caps() reads snap_trace_len from the wire-format

ceph_mds_caps header and uses it unconditionally to build a fake

end pointer (snaptrace + snaptrace_len) that is later handed to

ceph_update_snap_trace() in the CEPH_CAP_OP_IMPORT case:

snaptrace = h + 1;

snaptrace_len = le32_to_cpu(h->snap_trace_len);

p = snaptrace + snaptrace_len;

...

case CEPH_CAP_OP_IMPORT:

if (snaptrace_len) {

...

if (ceph_update_snap_trace(mdsc, snaptrace,

snaptrace + snaptrace_len,

false, &realm)) { ... }

ceph_update_snap_trace() then decodes a struct ceph_mds_snap_realm

from snaptrace using ceph_decode_need(&p, e, sizeof(*ri), bad)

with the attacker-supplied fake end e == snaptrace + snaptrace_len.

With snaptrace_len == 0xFFFFFFFF the bound check is trivially

satisfied, ri = p reads sizeof(struct ceph_mds_snap_realm) past

the legitimate msg->front buffer, and ri->num_snaps /

ri->num_prior_parent_snaps then drive further out-of-bounds

reads of the encoded snap arrays.

The eleven msg_version >= 2 .. msg_version >= 12 decoder blocks

above the op switch each catch this OOB through their

ceph_decode_*_safe() / ceph_decode_need() 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 snap_trace_len. The

shape has been present since ceph_handle_caps() was introduced.

Validate snap_trace_len against the message front buffer before

consuming it, using the canonical ceph_decode_need() / ceph_has_room()

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 + snap_trace_len could overflow the address space. This matches the

rest of the ceph decode path (e.g. the pool_ns_len check a few lines

below), and the existing goto bad cleanup already covers this exit

path. (NVD)

References