CVE-2026-72379 (GCVE-0-2026-72379)
Vulnerability from cvelistv5
Published
2026-08-15 05:56
Modified
2026-08-17 05:13
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: fs: refuse O_TMPFILE creation with an unmapped fsuid or fsgid vfs_tmpfile() never checked that the caller's fsuid and fsgid map into the filesystem. On an idmapped mount whose idmapping does not cover the caller's fs{u,g}id, the ->tmpfile() instance initializes the new inode through inode_init_owner(), where mapped_fsuid()/mapped_fsgid() return INVALID_UID/INVALID_GID, and the tmpfile ends up owned by (uid_t)-1. Every other creation path already refuses this: may_o_create() (O_CREAT) and may_create_dentry() (mkdir, mknod, symlink, link) bail out with -EOVERFLOW via fsuidgid_has_mapping() precisely so that an object cannot be created with an owner the filesystem cannot represent. An O_TMPFILE is no exception: it is created I_LINKABLE and linkat(2) can splice it into the namespace afterwards, so the same guarantee must hold. Add the missing fsuidgid_has_mapping() check to vfs_tmpfile(). On a non-idmapped mount the caller's fs{u,g}id always map in the superblock's user namespace, so this is a no-op there and only takes effect on an idmapped mount that does not map the caller. It applies to every filesystem that sets FS_ALLOW_IDMAP and implements ->tmpfile() (tmpfs, ext4, btrfs, xfs, f2fs, ...), and to overlayfs, whose upper-layer tmpfile creation funnels through vfs_tmpfile() via backing_tmpfile_open().
References
Impacted products
Vendor Product Version
Linux Linux Version: 8e5389132ab429604c1a2459b52f0c849a71cc61
Version: 8e5389132ab429604c1a2459b52f0c849a71cc61
Version: 8e5389132ab429604c1a2459b52f0c849a71cc61
Version: 8e5389132ab429604c1a2459b52f0c849a71cc61
Version: 8e5389132ab429604c1a2459b52f0c849a71cc61
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/namei.c"
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          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.13"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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              "lessThanOrEqual": "6.6.*",
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              "version": "6.6.145",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.97",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.40",
              "versionType": "semver"
            },
            {
              "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:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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              "negate": false,
              "operator": "OR"
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          ]
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs: refuse O_TMPFILE creation with an unmapped fsuid or fsgid\n\nvfs_tmpfile() never checked that the caller\u0027s fsuid and fsgid map into\nthe filesystem.  On an idmapped mount whose idmapping does not cover the\ncaller\u0027s fs{u,g}id, the -\u003etmpfile() instance initializes the new inode\nthrough inode_init_owner(), where mapped_fsuid()/mapped_fsgid() return\nINVALID_UID/INVALID_GID, and the tmpfile ends up owned by (uid_t)-1.\n\nEvery other creation path already refuses this: may_o_create() (O_CREAT)\nand may_create_dentry() (mkdir, mknod, symlink, link) bail out with\n-EOVERFLOW via fsuidgid_has_mapping() precisely so that an object cannot\nbe created with an owner the filesystem cannot represent.  An O_TMPFILE\nis no exception: it is created I_LINKABLE and linkat(2) can splice it\ninto the namespace afterwards, so the same guarantee must hold.\n\nAdd the missing fsuidgid_has_mapping() check to vfs_tmpfile().  On a\nnon-idmapped mount the caller\u0027s fs{u,g}id always map in the superblock\u0027s\nuser namespace, so this is a no-op there and only takes effect on an\nidmapped mount that does not map the caller.  It applies to every\nfilesystem that sets FS_ALLOW_IDMAP and implements -\u003etmpfile() (tmpfs,\next4, btrfs, xfs, f2fs, ...), and to overlayfs, whose upper-layer\ntmpfile creation funnels through vfs_tmpfile() via backing_tmpfile_open()."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:13:31.893Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/bac8fb0d60254846f3b56957435dcd870ae12948"
        },
        {
          "url": "https://git.kernel.org/stable/c/503d0568a525b168d9aa5ca046ec72fc5477df84"
        },
        {
          "url": "https://git.kernel.org/stable/c/a2038514e69371eb493083a6a897ed20fcbb8acb"
        },
        {
          "url": "https://git.kernel.org/stable/c/47e434da476b5a8bcd1e6e52ab03c5ee7764ee78"
        },
        {
          "url": "https://git.kernel.org/stable/c/539dce1144651f7976fa418e618b0b574bf15eeb"
        }
      ],
      "title": "fs: refuse O_TMPFILE creation with an unmapped fsuid or fsgid",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-72379",
    "datePublished": "2026-08-15T05:56:12.251Z",
    "dateReserved": "2026-08-09T03:40:39.922Z",
    "dateUpdated": "2026-08-17T05:13:31.893Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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