CVE-2026-68082 (GCVE-0-2026-68082)
Vulnerability from cvelistv5
Published
2026-08-08 09:17
Modified
2026-08-23 12:45
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
libceph: fix two unsafe bare decodes in decode_lockers()
decode_lockers() in cls_lock_client.c contains two bare decode operations
that allow a malicious or compromised OSD to trigger slab-out-of-bounds
reads:
1. ceph_decode_32(p) at the num_lockers field has no preceding bounds
check. ceph_start_decoding() accepts struct_len=0 as valid -- the
internal ceph_decode_need(p, end, 0, bad) always passes -- so when an
OSD sends struct_len=0, ceph_start_decoding() returns success with
p == end. The immediately following bare ceph_decode_32(p) then reads
4 bytes past the validated buffer boundary. The garbage value is
passed directly to kzalloc_objs() as the locker count.
The sibling function decode_watchers() in osd_client.c already uses
ceph_decode_32_safe() after its own ceph_start_decoding() call.
decode_lockers() was the only site using the bare variant.
2. ceph_decode_8(p) after the decode_locker() loop has no preceding
bounds check. If an OSD crafts num_lockers such that the loop
advances p exactly to end, the subsequent bare ceph_decode_8(p) reads
one byte past the validated buffer boundary. The result is passed
directly into *type, which is used as a lock type discriminator by
callers, giving an OSD-controlled one-byte OOB read with direct
influence over the lock type field.
Fix both by replacing bare operations with their safe variants:
ceph_decode_32(p) -> ceph_decode_32_safe(p, end, *num_lockers,
err_inval)
ceph_decode_8(p) -> ceph_decode_8_safe(p, end, *type,
err_free_lockers)
The goto targets differ intentionally:
err_inval: is a new label returning -EINVAL directly. It is used for
the pre-allocation failure path where *lockers is not yet allocated
and must not be passed to ceph_free_lockers().
err_free_lockers: is the existing label. It is used for the
post-allocation failure path where *lockers is allocated and must
be freed.
ret is set to -EINVAL before ceph_decode_8_safe() so that
err_free_lockers returns the correct error code on bounds violation.
Without this, err_free_lockers would return a stale ret value (0 from
the successful decode_locker() loop), silently swallowing the error.
-EINVAL is correct for both failure paths. The data received from the
OSD is structurally malformed. -ENOMEM would misrepresent the failure
class to callers and to stable@ backporters triaging error paths.
Attacker model: a malicious or compromised OSD in a multi-tenant Ceph
deployment can trigger this against any kernel client that issues the
lock.get_info class method (e.g. during RBD exclusive lock acquisition).
[ idryomov: trim changelog, formatting ]
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: d4ed4a530562881cc5225050e42d96034f405aae Version: d4ed4a530562881cc5225050e42d96034f405aae Version: d4ed4a530562881cc5225050e42d96034f405aae Version: d4ed4a530562881cc5225050e42d96034f405aae Version: d4ed4a530562881cc5225050e42d96034f405aae Version: d4ed4a530562881cc5225050e42d96034f405aae Version: d4ed4a530562881cc5225050e42d96034f405aae Version: d4ed4a530562881cc5225050e42d96034f405aae |
||
{
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nlibceph: fix two unsafe bare decodes in decode_lockers()\n\ndecode_lockers() in cls_lock_client.c contains two bare decode operations\nthat allow a malicious or compromised OSD to trigger slab-out-of-bounds\nreads:\n\n1. ceph_decode_32(p) at the num_lockers field has no preceding bounds\n check. ceph_start_decoding() accepts struct_len=0 as valid -- the\n internal ceph_decode_need(p, end, 0, bad) always passes -- so when an\n OSD sends struct_len=0, ceph_start_decoding() returns success with\n p == end. The immediately following bare ceph_decode_32(p) then reads\n 4 bytes past the validated buffer boundary. The garbage value is\n passed directly to kzalloc_objs() as the locker count.\n\n The sibling function decode_watchers() in osd_client.c already uses\n ceph_decode_32_safe() after its own ceph_start_decoding() call.\n decode_lockers() was the only site using the bare variant.\n\n2. ceph_decode_8(p) after the decode_locker() loop has no preceding\n bounds check. If an OSD crafts num_lockers such that the loop\n advances p exactly to end, the subsequent bare ceph_decode_8(p) reads\n one byte past the validated buffer boundary. The result is passed\n directly into *type, which is used as a lock type discriminator by\n callers, giving an OSD-controlled one-byte OOB read with direct\n influence over the lock type field.\n\nFix both by replacing bare operations with their safe variants:\n ceph_decode_32(p) -\u003e ceph_decode_32_safe(p, end, *num_lockers,\n err_inval)\n ceph_decode_8(p) -\u003e ceph_decode_8_safe(p, end, *type,\n err_free_lockers)\n\nThe goto targets differ intentionally:\n err_inval: is a new label returning -EINVAL directly. It is used for\n the pre-allocation failure path where *lockers is not yet allocated\n and must not be passed to ceph_free_lockers().\n\n err_free_lockers: is the existing label. It is used for the\n post-allocation failure path where *lockers is allocated and must\n be freed.\n\nret is set to -EINVAL before ceph_decode_8_safe() so that\nerr_free_lockers returns the correct error code on bounds violation.\nWithout this, err_free_lockers would return a stale ret value (0 from\nthe successful decode_locker() loop), silently swallowing the error.\n\n-EINVAL is correct for both failure paths. The data received from the\nOSD is structurally malformed. -ENOMEM would misrepresent the failure\nclass to callers and to stable@ backporters triaging error paths.\n\nAttacker model: a malicious or compromised OSD in a multi-tenant Ceph\ndeployment can trigger this against any kernel client that issues the\nlock.get_info class method (e.g. during RBD exclusive lock acquisition).\n\n[ idryomov: trim changelog, formatting ]"
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 9.8,
"baseSeverity": "CRITICAL",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:N - The flaw is reached when libceph decodes a crafted MOSDOpReply for the lock.get_info class method received over the Ceph messenger TCP session from a compromised or malicious OSD; no local syscall or ioctl is required on the victim.\nAC:L - A malicious OSD can deterministically send struct_len=0 or craft num_lockers so the decode pointer reaches end, triggering both bare decodes on every attempt without races, special memory layout, or rare kernel configuration.\nPR:N - The attacker acts as the remote Ceph OSD peer and needs no account or privileges on the victim Linux host; any kernel RBD client connected to a multi-tenant or attacker-controlled cluster is exposed during automatic exclusive-lock operations.\nUI:N - Once an RBD image is mapped, ceph_cls_lock_info() is invoked automatically during exclusive-lock acquisition and object-map lock recovery; no further victim user or administrator action is required at exploit time.\nS:U - The slab out-of-bounds reads and any resulting kernel memory corruption occur entirely within the victim host kernel running the Ceph client, without crossing VM, container, or IOMMU security boundaries.\nC:H - Bare ceph_decode_32/8 past the validated reply boundary perform slab out-of-bounds reads of adjacent kernel memory; the leaked u32 can drive kzalloc_objs() sizing and the OOB u8 directly controls the lock-type field consumed by RBD lock logic.\nI:H - Attacker-influenced out-of-bounds values feed heap allocation sizing and lock-type discrimination in kernel lock-handling paths, providing memory-corruption primitives in a privileged parser that can be leveraged beyond simple information disclosure.\nA:H - Slab out-of-bounds reads can trigger KASAN faults or kernel oops on instrumented builds, and attacker-controlled locker counts can force very large kzalloc attempts causing severe memory pressure, OOM conditions, and loss of availability on RBD client hosts."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-23T12:45:46.891Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/c8ade01170a27d8ede0d761c255268af81e417f8"
},
{
"url": "https://git.kernel.org/stable/c/001835c599899ef1bd3506a815110a6374451554"
},
{
"url": "https://git.kernel.org/stable/c/7c422364acd93d7da1dfc27d6b54635a269653a1"
},
{
"url": "https://git.kernel.org/stable/c/02430f6f729b297e803d0605871f0a670b4eafd6"
},
{
"url": "https://git.kernel.org/stable/c/57ba829804fe6d34bbac3b826c4b15c1caa54862"
},
{
"url": "https://git.kernel.org/stable/c/89df5d71f83f8e2781286798fd8ae5e42cf5f1a7"
},
{
"url": "https://git.kernel.org/stable/c/a54be593d0b749161b08a1e56189b2cb9114267a"
},
{
"url": "https://git.kernel.org/stable/c/a109a556115271ca7896dcda7b4b7e45e156c227"
}
],
"title": "libceph: fix two unsafe bare decodes in decode_lockers()",
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"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-68082",
"datePublished": "2026-08-08T09:17:45.394Z",
"dateReserved": "2026-07-30T09:28:09.367Z",
"dateUpdated": "2026-08-23T12:45:46.891Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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