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FKIE_CVE-2026-72379

Vulnerability from fkie_nvd - Published: 2026-08-15 06:22 - Updated: 2026-08-17 06:18
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
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/47e434da476b5a8bcd1e6e52ab03c5ee7764ee78
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/503d0568a525b168d9aa5ca046ec72fc5477df84
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/539dce1144651f7976fa418e618b0b574bf15eeb
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a2038514e69371eb493083a6a897ed20fcbb8acb
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/bac8fb0d60254846f3b56957435dcd870ae12948
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/namei.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "bac8fb0d60254846f3b56957435dcd870ae12948",
              "status": "affected",
              "version": "8e5389132ab429604c1a2459b52f0c849a71cc61",
              "versionType": "git"
            },
            {
              "lessThan": "503d0568a525b168d9aa5ca046ec72fc5477df84",
              "status": "affected",
              "version": "8e5389132ab429604c1a2459b52f0c849a71cc61",
              "versionType": "git"
            },
            {
              "lessThan": "a2038514e69371eb493083a6a897ed20fcbb8acb",
              "status": "affected",
              "version": "8e5389132ab429604c1a2459b52f0c849a71cc61",
              "versionType": "git"
            },
            {
              "lessThan": "47e434da476b5a8bcd1e6e52ab03c5ee7764ee78",
              "status": "affected",
              "version": "8e5389132ab429604c1a2459b52f0c849a71cc61",
              "versionType": "git"
            },
            {
              "lessThan": "539dce1144651f7976fa418e618b0b574bf15eeb",
              "status": "affected",
              "version": "8e5389132ab429604c1a2459b52f0c849a71cc61",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/namei.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.13"
            },
            {
              "lessThan": "5.13",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.145",
              "versionType": "semver"
            },
            {
              "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"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "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()."
    }
  ],
  "id": "CVE-2026-72379",
  "lastModified": "2026-08-17T06:18:42.283",
  "metrics": {},
  "published": "2026-08-15T06:22:11.387",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/47e434da476b5a8bcd1e6e52ab03c5ee7764ee78"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/503d0568a525b168d9aa5ca046ec72fc5477df84"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/539dce1144651f7976fa418e618b0b574bf15eeb"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/a2038514e69371eb493083a6a897ed20fcbb8acb"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/bac8fb0d60254846f3b56957435dcd870ae12948"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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