FKIE_CVE-2026-74483

Vulnerability from fkie_nvd - Published: 2026-08-15 13:17 - Updated: 2026-08-23 13:16
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: binfmt_misc: don't leak the user namespace when the mount fails bm_get_tree() takes a reference to the user namespace and hands it to get_tree_keyed() as the sget key. sget_fc() moves that reference into sb->s_fs_info and clears fc->s_fs_info, so from that point on the superblock owns it and bm_free() doesn't see it anymore. The superblock drops it in ->put_super(). But generic_shutdown_super() only calls ->put_super() from inside the if (sb->s_root) branch, so nothing releases it when bm_fill_super() fails: - The kzalloc_obj() failure leaves s_root NULL and the whole branch is skipped. - A simple_fill_super() failure in the file loop leaves s_root set, but s_op still points at simple_super_operations, which has no ->put_super(). bm_fill_super() installs s_ops only once simple_fill_super() returned success, and installing it earlier wouldn't help either because simple_fill_super() overwrites s_op. Either way vfs_get_super() calls deactivate_locked_super() and the reference is gone for good. binfmt_misc mounts are available in a user namespace and both the inode and the dentry cache are SLAB_ACCOUNT, so an unprivileged caller under a tight memory cgroup can fail simple_fill_super() on demand and leak one user namespace per attempt. Drop the reference in ->kill_sb() instead, which runs unconditionally, the same way nfsd and rpc_pipefs release their keyed s_fs_info. That also stops ->put_super() from clearing s_fs_info while the superblock is still on @fs_supers. generic_shutdown_super() leaves it there on purpose so that sget_fc() keeps finding it until kill_sb() has run, but a NULL s_fs_info makes test_keyed_super() miss it, so a concurrent mount for the same user namespace skips the grab_super() wait and creates a second superblock for a namespace that is still being torn down.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/867aed6a4848761190d5ebdedf9642648f97bceb
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/87a4eb9bbb3497f749bbac612af22ddaa62d7b0d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b8206f516fe7cbe785cf44bf09c17c438d7c3cad
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ffec017158d3aad8a6ffca1dfad63d63bde9caad
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/binfmt_misc.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "ffec017158d3aad8a6ffca1dfad63d63bde9caad",
              "status": "affected",
              "version": "21ca59b365c091d583f36ac753eaa8baf947be6f",
              "versionType": "git"
            },
            {
              "lessThan": "867aed6a4848761190d5ebdedf9642648f97bceb",
              "status": "affected",
              "version": "21ca59b365c091d583f36ac753eaa8baf947be6f",
              "versionType": "git"
            },
            {
              "lessThan": "87a4eb9bbb3497f749bbac612af22ddaa62d7b0d",
              "status": "affected",
              "version": "21ca59b365c091d583f36ac753eaa8baf947be6f",
              "versionType": "git"
            },
            {
              "lessThan": "b8206f516fe7cbe785cf44bf09c17c438d7c3cad",
              "status": "affected",
              "version": "21ca59b365c091d583f36ac753eaa8baf947be6f",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/binfmt_misc.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.7"
            },
            {
              "lessThan": "6.7",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.105",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.46",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.8",
              "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\nbinfmt_misc: don\u0027t leak the user namespace when the mount fails\n\nbm_get_tree() takes a reference to the user namespace and hands it to\nget_tree_keyed() as the sget key. sget_fc() moves that reference into\nsb-\u003es_fs_info and clears fc-\u003es_fs_info, so from that point on the\nsuperblock owns it and bm_free() doesn\u0027t see it anymore.\n\nThe superblock drops it in -\u003eput_super(). But generic_shutdown_super()\nonly calls -\u003eput_super() from inside the if (sb-\u003es_root) branch, so\nnothing releases it when bm_fill_super() fails:\n\n- The kzalloc_obj() failure leaves s_root NULL and the whole branch is\n  skipped.\n\n- A simple_fill_super() failure in the file loop leaves s_root set, but\n  s_op still points at simple_super_operations, which has no\n  -\u003eput_super(). bm_fill_super() installs s_ops only once\n  simple_fill_super() returned success, and installing it earlier\n  wouldn\u0027t help either because simple_fill_super() overwrites s_op.\n\nEither way vfs_get_super() calls deactivate_locked_super() and the\nreference is gone for good. binfmt_misc mounts are available in a user\nnamespace and both the inode and the dentry cache are SLAB_ACCOUNT, so\nan unprivileged caller under a tight memory cgroup can fail\nsimple_fill_super() on demand and leak one user namespace per attempt.\n\nDrop the reference in -\u003ekill_sb() instead, which runs unconditionally,\nthe same way nfsd and rpc_pipefs release their keyed s_fs_info.\n\nThat also stops -\u003eput_super() from clearing s_fs_info while the\nsuperblock is still on @fs_supers. generic_shutdown_super() leaves it\nthere on purpose so that sget_fc() keeps finding it until kill_sb() has\nrun, but a NULL s_fs_info makes test_keyed_super() miss it, so a\nconcurrent mount for the same user namespace skips the grab_super()\nwait and creates a second superblock for a namespace that is still\nbeing torn down."
    }
  ],
  "id": "CVE-2026-74483",
  "lastModified": "2026-08-23T13:16:44.530",
  "metrics": {},
  "published": "2026-08-15T13:17:53.163",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/867aed6a4848761190d5ebdedf9642648f97bceb"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/87a4eb9bbb3497f749bbac612af22ddaa62d7b0d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b8206f516fe7cbe785cf44bf09c17c438d7c3cad"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ffec017158d3aad8a6ffca1dfad63d63bde9caad"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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