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eventpoll: don't decrement ep refcount while still holding the ep mutex

Type: advisorySource: Official CVE List1 source record

In the Linux kernel, the following vulnerability has been resolved: eventpoll: don't decrement ep refcount while still holding the ep mutex Jann Horn points out that epoll is decrementing the ep refcount and then doing a mutex_unlock(&ep->mtx); afterwards. That's very wrong, because it can lead to a use-after-free. That pattern is actually fine for the very last reference, because the code in question will delay the actual call to "ep_free(ep)" until after it has unlocked the mutex. But it's wrong for the much subtler "next to last" case when somebody *else* may also be dropping their reference and free the ep while we're still using the mutex. Note that this is true even if that other user is also using the same ep mutex: mutexes, unlike spinlocks, can not be used for object ownership, even if they guarantee mutual exclusion. A mutex "unlock" operation is not atomic, and as one user is still accessing the mutex as part of unlocking it, another user can come in and get the now released mutex and free the data structure while the first user is still cleaning up. See our mutex documentation in Documentation/locking/mutex-design.rst, in particular the section [1] about semantics: "mutex_unlock() may access the mutex structure even after it has internally released the lock already - so it's not safe for another context to acquire the mutex and assume that the mutex_unlock() context is not using the structure anymore" So if we drop our ep ref before the mutex unlock, but we weren'

Announced Source revision 1
Original source ↗

CVE-2025-38349

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2025-38349

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
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Prerequisites
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Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "f2451def095c1743adcfcb0cb5dadc86034e162a",
        "lessThan": "263f5de8302a6f2f136d392e5d3f8b1edf922857",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "a1f93804449d13f97dabd4b996817de4bf1ed67a",
        "lessThan": "b0821ec902d39062356cb644c16e17a705d1c9f5",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "58c9b016e12855286370dfb704c08498edbc857a",
        "lessThan": "521e9ff0b67c66a17d6f9593dfccafaa984aae4c",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "58c9b016e12855286370dfb704c08498edbc857a",
        "lessThan": "6dee745bd0aec9d399df674256e7b1ecdb615444",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "58c9b016e12855286370dfb704c08498edbc857a",
        "lessThan": "605c18698ecfa99165f36b7f59d3ed503e169814",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "58c9b016e12855286370dfb704c08498edbc857a",
        "lessThan": "8c2e52ebbe885c7eeaabd3b7ddcdc1246fc400d2",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "5.15.209",
        "lessThan": "5.15.222",
        "versionType": "semver"
      },
      {
        "status": "affected",
        "version": "6.1.175",
        "lessThan": "6.1.178",
        "versionType": "semver"
      }
    ],
    "programFiles": [
      "fs/eventpoll.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "6.4"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "6.4",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "5.15.222",
        "versionType": "semver",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.1.178",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.99",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.39",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.15.7",
        "versionType": "semver",
        "lessThanOrEqual": "6.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.16",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "fs/eventpoll.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2025-38349

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#8239 · Revision 1
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Publisher date
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