CVE-2026-89657

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

libceph: validate OSD extent maps before cursor advance

net/ceph/osd_client.c:osd_sparse_read() validates that the sparse-read
data length matches the summed extent lengths, but it does not validate
that each OSD-supplied extent is monotonic and lies inside the original
request range. A malformed authenticated OSD reply can advertise a
far-forward nonzero extent offset with a matching data length and make
the client advance the message-data cursor beyond the request buffer.
This reaches the BUG_ON(!*length) assertion in ceph_msg_data_next() from
the client receive path.

Impact: A malicious or compromised authenticated Ceph OSD peer can crash
a kernel Ceph client via a malformed sparse-read reply.

Reject sparse extent maps that overflow, move backwards, overlap, or
extend outside the original sparse-read request before advancing the
cursor.

[ idryomov: perform sparse_extent_map_valid() check a bit earlier,
  in CEPH_SPARSE_READ_DATA_LEN instead of CEPH_SPARSE_READ_DATA_PRE
  state ]