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.