CVE-2026-93100

Full vulnerability record from the local CVENow database.

Description

In the Linux kernel, the following vulnerability has been resolved: fs/resctrl: Prevent use-after-free in rdtgroup_kn_put() A struct rdtgroup is reference counted via rdtgroup::waitcount. Callers that need the structure to remain valid across a sleep (while waiting on acquiring rdtgroup_mutex) take a reference with rdtgroup_kn_get() and release it with rdtgroup_kn_put(). The release path is intended to serve as the fallback freer: if the count drops to zero and the group has already been marked RDT_DELETED, rdtgroup_kn_put() frees the structure. The bulk teardown paths free_all_child_rdtgrp() and rmdir_all_sub() resulting from a resctrl directory remove or resctrl fs unmount act as the primary freer: they hold rdtgroup_mutex and free each rdtgroup whose waitcount is zero, otherwise they set RDT_DELETED and leave the freeing to the last waiter. These two freers race. rdtgroup_kn_put() commits waitcount == 0 with atomic_dec_and_test() outside rdtgroup_mutex, then reads rdtgroup::flags. Between those two operations a concurrent caller of free_all_child_rdtgrp() or rmdir_all_sub() (which holds the mutex) can observe waitcount == 0 via atomic_read(), call rdtgroup_remove(), and kfree() the structure. The subsequent read of rdtgroup::flags in rdtgroup_kn_put() is then a use-after-free, and the structure may even be freed twice if the freed memory happens to satisfy the RDT_DELETED flag check. Replace the bare atomic_dec_and_test() with atomic_dec_and_mutex_lock() so that the decrement-to-zero takes rdtgroup_mutex before the count becomes globally visible. The inspection of rdtgroup::flags then runs under the same mutex held by the bulk freers, making the two paths mutually exclusive. The common case where the count does not reach zero remains lock-free. Defer kernfs_unbreak_active_protection() until after the mutex is dropped since kernfs active protections functionally wrap rdtgroup_mutex. Remove resource group, which in turn drops its kernfs reference, after kernfs protection is restored. [ bp: Split the commit messsages into smaller, easier-parseable paragraphs. ]

Severity

Not scored

CVSS score

Not available

Vulnerability status

Received

Source identifier

416baaa9-dc9f-4396-8d5f-8c081fb06d67

Published

2026-09-17 17:18:04.223000

Last modified

2026-10-30 13:20:57.240000

View original CVE JSON

{
  "id": "CVE-2026-93100",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2026-09-17T17:18:04.223",
  "lastModified": "2026-10-30T13:20:57.240",
  "vulnStatus": "Received",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs/resctrl: Prevent use-after-free in rdtgroup_kn_put()\n\nA struct rdtgroup is reference counted via rdtgroup::waitcount. Callers that\nneed the structure to remain valid across a sleep (while waiting on acquiring\nrdtgroup_mutex) take a reference with rdtgroup_kn_get() and release it with\nrdtgroup_kn_put().\n\nThe release path is intended to serve as the fallback freer: if the count\ndrops to zero and the group has already been marked RDT_DELETED,\nrdtgroup_kn_put() frees the structure.\n\nThe bulk teardown paths free_all_child_rdtgrp() and rmdir_all_sub() resulting\nfrom a resctrl directory remove or resctrl fs unmount act as the primary\nfreer: they hold rdtgroup_mutex and free each rdtgroup whose waitcount is\nzero, otherwise they set RDT_DELETED and leave the freeing to the last waiter.\n\nThese two freers race. rdtgroup_kn_put() commits waitcount == 0 with\natomic_dec_and_test() outside rdtgroup_mutex, then reads rdtgroup::flags.\nBetween those two operations a concurrent caller of free_all_child_rdtgrp()\nor rmdir_all_sub() (which holds the mutex) can observe waitcount == 0 via\natomic_read(), call rdtgroup_remove(), and kfree() the structure.\n\nThe subsequent read of rdtgroup::flags in rdtgroup_kn_put() is then\na use-after-free, and the structure may even be freed twice if the freed\nmemory happens to satisfy the RDT_DELETED flag check.\n\nReplace the bare atomic_dec_and_test() with atomic_dec_and_mutex_lock() so\nthat the decrement-to-zero takes rdtgroup_mutex before the count becomes\nglobally visible. The inspection of rdtgroup::flags then runs under the same\nmutex held by the bulk freers, making the two paths mutually exclusive.\n\nThe common case where the count does not reach zero remains lock-free. Defer\nkernfs_unbreak_active_protection() until after the mutex is dropped since\nkernfs active protections functionally wrap rdtgroup_mutex. Remove resource\ngroup, which in turn drops its kernfs reference, after kernfs protection is\nrestored.\n\n  [ bp: Split the commit messsages into smaller, easier-parseable paragraphs. ]"
    }
  ],
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "programFiles": [
            "fs/resctrl/rdtgroup.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "b8511ccc75c033f6d54188ea4df7bf1e85778740",
              "lessThan": "906b3044dbf7c38cc411f7cf457c811363161e3b",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "b8511ccc75c033f6d54188ea4df7bf1e85778740",
              "lessThan": "971b40e3ca1279ca4917889e0195d33b66d071a4",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "b8511ccc75c033f6d54188ea4df7bf1e85778740",
              "lessThan": "828ff461c136b95d13b8d712c0a7a06a640e313a",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "b8511ccc75c033f6d54188ea4df7bf1e85778740",
              "lessThan": "ae69f936e8ffed553d899ba4c02f8a7461a89e54",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "b8511ccc75c033f6d54188ea4df7bf1e85778740",
              "lessThan": "4c593c62c1499665baebbb41b70e2c9b7e947b86",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "b8511ccc75c033f6d54188ea4df7bf1e85778740",
              "lessThan": "f5bcf539484d2d604c2f2330e09487ea090b21c7",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "d20edc0bca5577bab38acb5b190619c922ddebf8",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "1b006f8cbde9f3dabdfafe2ff7aa9f831ed5b625",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "40300f986e47dbc8f1d02e5080385f5cf9f85f70",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "b5a4949897ebada8132d54c93208989482503103",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "4.14.170",
              "lessThan": "4.15",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "4.19.102",
              "lessThan": "4.20",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "5.4.18",
              "lessThan": "5.5",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "5.5.2",
              "lessThan": "5.6",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "affected",
          "programFiles": [
            "fs/resctrl/rdtgroup.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "5.6",
              "status": "affected"
            },
            {
              "version": "0",
              "lessThan": "5.6",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.1.191",
              "lessThanOrEqual": "6.1.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.6.160",
              "lessThanOrEqual": "6.6.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.12.114",
              "lessThanOrEqual": "6.12.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.18.52",
              "lessThanOrEqual": "6.18.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.2.6",
              "lessThanOrEqual": "7.2.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.3",
              "lessThanOrEqual": "*",
              "versionType": "original_commit_for_fix",
              "status": "unaffected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {},
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/4c593c62c1499665baebbb41b70e2c9b7e947b86",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/828ff461c136b95d13b8d712c0a7a06a640e313a",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/906b3044dbf7c38cc411f7cf457c811363161e3b",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/971b40e3ca1279ca4917889e0195d33b66d071a4",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/ae69f936e8ffed553d899ba4c02f8a7461a89e54",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/f5bcf539484d2d604c2f2330e09487ea090b21c7",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ]
}