ceph: cap delegated inode count in ceph_parse_deleg_inos()

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89648
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-11 20:19:50 UTC
Updated2026-09-11 20:19:50 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: ceph: cap delegated inode count in ceph_parse_deleg_inos() ceph_parse_deleg_inos() decodes interval sets of delegated inode numbers from an MDS create-with-delegation reply. For each set it reads a 64-bit start and a 64-bit len with ceph_decode_64_safe(), which only validates that the eight bytes are present in the message, not the value, and then loops over len while inserting entries into s_delegated_inos. len is fully attacker controlled. A malicious or compromised MDS can send one huge interval, many intervals in one reply, duplicate intervals, or repeated replies that accumulate delegated inodes on the same session. The original code bounded none of these and could spin the insert loop or grow the xarray without limit. Bound both dimensions with a single enforcement point. Track the number of delegated inodes held by each MDS session in an atomic counter and grow it only in ceph_insert_deleg_ino(), which uses atomic_add_unless() to refuse to push the count past CEPH_MAX_DELEG_INOS. Because that helper is the only place the counter grows, the per-session population can never exceed the cap, so no separate per-session pre-check is needed. The counter is decremented when async create consumes a delegated inode or when an insert fails, incremented when a delegated inode is restored, initialized with the session xarray, and reset when reconnect destroys the xarray. A per-session cap alone still lets one reply spin the insert loop on duplicate ranges without growing the counter, so also cap the aggregate interval length accepted from a single reply. Together these bound both the loop trip count per reply and the xarray population across replies. The cap is a fixed, client-chosen constant rather than a value derived from the MDS. mds_client_prealloc_inos is a userspace MDS configuration option; it is never sent to the kernel client on the wire, and a server-supplied bound could not be trusted for a defensive limit in any case. The constant is set well above that option's documented default of 1000 (a generous multiple), so legitimate refill behavior is unaffected while the CPU and xarray memory a malformed delegation stream can consume stays bounded. Impact: a malicious or compromised Ceph MDS can no longer make a client spin through an unbounded delegated-inode interval or grow one session's delegated-inode xarray without limit.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected d4846487870897a5a149a3220c95bfd5728f9247 c040e139f1a629b767f900bbbc3f9892c290ed85 git Not specified
CNA Linux Linux affected d4846487870897a5a149a3220c95bfd5728f9247 f341270ac5f5077804d7837ce77b0f0df1cea29d git Not specified
CNA Linux Linux affected d4846487870897a5a149a3220c95bfd5728f9247 4bd3158bd62466d57ed72a3f7bc5f205fedd6919 git Not specified
CNA Linux Linux affected 5.7 Not specified
CNA Linux Linux unaffected 5.7 semver Not specified
CNA Linux Linux unaffected 6.18.51 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.4 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/4bd3158bd62466d57ed72a3f7bc5f205fedd6919 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f341270ac5f5077804d7837ce77b0f0df1cea29d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/c040e139f1a629b767f900bbbc3f9892c290ed85 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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