Vulnerability-Lookup

GHSA-C5W7-7J2G-7V27

Vulnerability from github – Published: 2026-08-15 06:32 – Updated: 2026-08-15 06:32

Details

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

kernfs: link kn to its parent before the LSM init hook

After commit 12e9e3cd03b5 ("simpe_xattr: use per-sb cache"), kernfs_xattr_set() and kernfs_xattr_get() compute the cache via kernfs_root(kn) before any other check. kernfs_root(kn) walks kn->__parent first and falls back to kn->dir.root, both of which are NULL on a freshly kmem_cache_zalloc()'d kn. kn->__parent was being set in kernfs_new_node() after __kernfs_new_node() returned, and kn->dir.root is set even later by kernfs_create_dir_ns() / kernfs_create_empty_dir().

The LSM kernfs_init_security hook is invoked from inside __kernfs_new_node(), before either field has been initialized. selinux_kernfs_init_security() ends with kernfs_xattr_set(kn, XATTR_NAME_SELINUX, ...). kernfs_root(kn) then returns NULL, and &((struct kernfs_root *)NULL)->xa_cache evaluates to offsetof(struct kernfs_root, xa_cache) which faults:

BUG: kernel NULL pointer dereference, address: 00000000000000e0 RIP: 0010:simple_xattr_set+0x27/0x8b0 Call Trace: kernfs_xattr_set+0x63/0xb0 selinux_kernfs_init_security+0x13b/0x270 security_kernfs_init_security+0x36/0xc0 __kernfs_new_node+0x182/0x290 kernfs_new_node+0x80/0xc0 kernfs_create_dir_ns+0x2b/0xa0 cgroup_create+0x116/0x380 cgroup_mkdir+0x7c/0x1a0

Reproduces deterministically at PID 1 (systemd) on an SELinux-enabled distro. The first cgroup mkdir under /sys/fs/cgroup with a labelled parent panics the kernel.

The LSM hook's contract is that the kn_dir argument is the parent of the new kn, so kn->__parent should already point at kn_dir when the hook runs. Move kernfs_get(parent) and rcu_assign_pointer of kn->__parent from kernfs_new_node() into __kernfs_new_node() right before the security hook, and unwind the parent reference on the err_out4 path. kernfs_root(kn) then takes its parent branch during the hook and returns parent->dir.root, which is the correct root.

This also closes the same-shape latent bug in kernfs_xattr_get() (which today is hidden only by kernfs_iattrs_noalloc() returning NULL on a fresh kn).

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{
  "affected": [],
  "aliases": [
    "CVE-2026-74342"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-15T06:22:35Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nkernfs: link kn to its parent before the LSM init hook\n\nAfter commit 12e9e3cd03b5 (\"simpe_xattr: use per-sb cache\"),\nkernfs_xattr_set() and kernfs_xattr_get() compute the cache via\nkernfs_root(kn) before any other check.  kernfs_root(kn) walks\nkn-\u003e__parent first and falls back to kn-\u003edir.root, both of which are\nNULL on a freshly kmem_cache_zalloc()\u0027d kn. kn-\u003e__parent was being set\nin kernfs_new_node() after __kernfs_new_node() returned, and kn-\u003edir.root\nis set even later by kernfs_create_dir_ns() / kernfs_create_empty_dir().\n\nThe LSM kernfs_init_security hook is invoked from inside\n__kernfs_new_node(), before either field has been initialized.\nselinux_kernfs_init_security() ends with kernfs_xattr_set(kn,\nXATTR_NAME_SELINUX, ...).  kernfs_root(kn) then returns NULL, and\n\u0026((struct kernfs_root *)NULL)-\u003exa_cache evaluates to\noffsetof(struct kernfs_root, xa_cache) which faults:\n\n  BUG: kernel NULL pointer dereference, address: 00000000000000e0\n  RIP: 0010:simple_xattr_set+0x27/0x8b0\n  Call Trace:\n   kernfs_xattr_set+0x63/0xb0\n   selinux_kernfs_init_security+0x13b/0x270\n   security_kernfs_init_security+0x36/0xc0\n   __kernfs_new_node+0x182/0x290\n   kernfs_new_node+0x80/0xc0\n   kernfs_create_dir_ns+0x2b/0xa0\n   cgroup_create+0x116/0x380\n   cgroup_mkdir+0x7c/0x1a0\n\nReproduces deterministically at PID 1 (systemd) on an SELinux-enabled\ndistro. The first cgroup mkdir under /sys/fs/cgroup with a labelled\nparent panics the kernel.\n\nThe LSM hook\u0027s contract is that the kn_dir argument is the parent of\nthe new kn, so kn-\u003e__parent should already point at kn_dir when the\nhook runs.  Move kernfs_get(parent) and rcu_assign_pointer of\nkn-\u003e__parent from kernfs_new_node() into __kernfs_new_node() right\nbefore the security hook, and unwind the parent reference on the\nerr_out4 path.  kernfs_root(kn) then takes its parent branch during\nthe hook and returns parent-\u003edir.root, which is the correct root.\n\nThis also closes the same-shape latent bug in kernfs_xattr_get() (which\ntoday is hidden only by kernfs_iattrs_noalloc() returning NULL on a\nfresh kn).",
  "id": "GHSA-c5w7-7j2g-7v27",
  "modified": "2026-08-15T06:32:30Z",
  "published": "2026-08-15T06:32:30Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-74342"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/319b82e8b46edaf557436ad858e734e583f78ec9"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6cccc49b027c7551ffc1d2532f2ef1922661f3da"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-74342 (GCVE-0-2026-74342)

Vulnerability from cvelistv5 – Published: 2026-08-15 05:58 – Updated: 2026-08-17 05:17

Title

kernfs: link kn to its parent before the LSM init hook

Summary

In the Linux kernel, the following vulnerability has been resolved: kernfs: link kn to its parent before the LSM init hook After commit 12e9e3cd03b5 ("simpe_xattr: use per-sb cache"), kernfs_xattr_set() and kernfs_xattr_get() compute the cache via kernfs_root(kn) before any other check. kernfs_root(kn) walks kn->__parent first and falls back to kn->dir.root, both of which are NULL on a freshly kmem_cache_zalloc()'d kn. kn->__parent was being set in kernfs_new_node() after __kernfs_new_node() returned, and kn->dir.root is set even later by kernfs_create_dir_ns() / kernfs_create_empty_dir(). The LSM kernfs_init_security hook is invoked from inside __kernfs_new_node(), before either field has been initialized. selinux_kernfs_init_security() ends with kernfs_xattr_set(kn, XATTR_NAME_SELINUX, ...). kernfs_root(kn) then returns NULL, and &((struct kernfs_root *)NULL)->xa_cache evaluates to offsetof(struct kernfs_root, xa_cache) which faults: BUG: kernel NULL pointer dereference, address: 00000000000000e0 RIP: 0010:simple_xattr_set+0x27/0x8b0 Call Trace: kernfs_xattr_set+0x63/0xb0 selinux_kernfs_init_security+0x13b/0x270 security_kernfs_init_security+0x36/0xc0 __kernfs_new_node+0x182/0x290 kernfs_new_node+0x80/0xc0 kernfs_create_dir_ns+0x2b/0xa0 cgroup_create+0x116/0x380 cgroup_mkdir+0x7c/0x1a0 Reproduces deterministically at PID 1 (systemd) on an SELinux-enabled distro. The first cgroup mkdir under /sys/fs/cgroup with a labelled parent panics the kernel. The LSM hook's contract is that the kn_dir argument is the parent of the new kn, so kn->__parent should already point at kn_dir when the hook runs. Move kernfs_get(parent) and rcu_assign_pointer of kn->__parent from kernfs_new_node() into __kernfs_new_node() right before the security hook, and unwind the parent reference on the err_out4 path. kernfs_root(kn) then takes its parent branch during the hook and returns parent->dir.root, which is the correct root. This also closes the same-shape latent bug in kernfs_xattr_get() (which today is hidden only by kernfs_iattrs_noalloc() returning NULL on a fresh kn).

Severity

No CVSS data available.

Assigner

Linux mitre root

References

2 references

URL	Tags
https://git.kernel.org/stable/c/319b82e8b46edaf55…
https://git.kernel.org/stable/c/6cccc49b027c7551f…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 319b82e8b46edaf557436ad858e734e583f78ec9 (git) Affected: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 , < 6cccc49b027c7551ffc1d2532f2ef1922661f3da (git) Affected: 0 , < 7.1.5 (semver)
Linux	Linux	Unaffected: 7.1.5 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/kernfs/dir.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "319b82e8b46edaf557436ad858e734e583f78ec9",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "6cccc49b027c7551ffc1d2532f2ef1922661f3da",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
              "lessThan": "7.1.5",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/kernfs/dir.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.5",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1.5",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nkernfs: link kn to its parent before the LSM init hook\n\nAfter commit 12e9e3cd03b5 (\"simpe_xattr: use per-sb cache\"),\nkernfs_xattr_set() and kernfs_xattr_get() compute the cache via\nkernfs_root(kn) before any other check.  kernfs_root(kn) walks\nkn-\u003e__parent first and falls back to kn-\u003edir.root, both of which are\nNULL on a freshly kmem_cache_zalloc()\u0027d kn. kn-\u003e__parent was being set\nin kernfs_new_node() after __kernfs_new_node() returned, and kn-\u003edir.root\nis set even later by kernfs_create_dir_ns() / kernfs_create_empty_dir().\n\nThe LSM kernfs_init_security hook is invoked from inside\n__kernfs_new_node(), before either field has been initialized.\nselinux_kernfs_init_security() ends with kernfs_xattr_set(kn,\nXATTR_NAME_SELINUX, ...).  kernfs_root(kn) then returns NULL, and\n\u0026((struct kernfs_root *)NULL)-\u003exa_cache evaluates to\noffsetof(struct kernfs_root, xa_cache) which faults:\n\n  BUG: kernel NULL pointer dereference, address: 00000000000000e0\n  RIP: 0010:simple_xattr_set+0x27/0x8b0\n  Call Trace:\n   kernfs_xattr_set+0x63/0xb0\n   selinux_kernfs_init_security+0x13b/0x270\n   security_kernfs_init_security+0x36/0xc0\n   __kernfs_new_node+0x182/0x290\n   kernfs_new_node+0x80/0xc0\n   kernfs_create_dir_ns+0x2b/0xa0\n   cgroup_create+0x116/0x380\n   cgroup_mkdir+0x7c/0x1a0\n\nReproduces deterministically at PID 1 (systemd) on an SELinux-enabled\ndistro. The first cgroup mkdir under /sys/fs/cgroup with a labelled\nparent panics the kernel.\n\nThe LSM hook\u0027s contract is that the kn_dir argument is the parent of\nthe new kn, so kn-\u003e__parent should already point at kn_dir when the\nhook runs.  Move kernfs_get(parent) and rcu_assign_pointer of\nkn-\u003e__parent from kernfs_new_node() into __kernfs_new_node() right\nbefore the security hook, and unwind the parent reference on the\nerr_out4 path.  kernfs_root(kn) then takes its parent branch during\nthe hook and returns parent-\u003edir.root, which is the correct root.\n\nThis also closes the same-shape latent bug in kernfs_xattr_get() (which\ntoday is hidden only by kernfs_iattrs_noalloc() returning NULL on a\nfresh kn)."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:17:34.554Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/319b82e8b46edaf557436ad858e734e583f78ec9"
        },
        {
          "url": "https://git.kernel.org/stable/c/6cccc49b027c7551ffc1d2532f2ef1922661f3da"
        }
      ],
      "title": "kernfs: link kn to its parent before the LSM init hook",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74342",
    "datePublished": "2026-08-15T05:58:31.924Z",
    "dateReserved": "2026-08-15T05:44:03.886Z",
    "dateUpdated": "2026-08-17T05:17:34.554Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

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GHSA-C5W7-7J2G-7V27

CVE-2026-74342 (GCVE-0-2026-74342)

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Nomenclature