CVE-2026-89649

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

ceph: bound xattr value length in __build_xattrs()

__build_xattrs() decodes the MDS-supplied xattr blob one attribute at a

time. For each attribute it reads a 32-bit name length, advances past the

name bytes, reads a 32-bit value length, records the value pointer, and

advances past the value bytes. The two length fields are read with

ceph_decode_32_safe(), but the value bytes themselves are advanced over

with a bare "p += len" and no ceph_decode_need() check that "len" bytes

remain in the blob.

For every attribute except the last, the next iteration's

ceph_decode_32_safe() on the following name length implicitly verifies

that the previous value did not run past the blob end. The final

attribute has no successor, so its decoded value length is never checked

against the blob bounds. A malicious or compromised metadata server can

set the last attribute's value length larger than the bytes actually

present in the blob.

The blob is a dedicated kvmalloc() allocation sized to the wire length

(ceph_buffer_new() in ceph_fill_inode()). __set_xattr() records the

oversized length in xattr->val_len verbatim, and a later getxattr(2) runs

memcpy(value, xattr->val, xattr->val_len) into a user-supplied buffer,

copying bytes past the end of the allocation back to user space.

Impact: a malicious metadata server discloses adjacent kernel heap bytes

to a local user via getxattr(2) on a CephFS file. Add the missing

ceph_decode_need() so an out-of-bounds value length on the final

attribute fails the decode and returns -EIO instead of being stored.