CVE-2026-98980 (GCVE-0-2026-98980)
Vulnerability from cvelistv5
Published
2026-10-23 12:19
Modified
2026-10-24 14:09
Severity ?
8.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: namei: don't reveal overmounted entries in refwalk In rcuwalk the dentry is validated before it is accepted. step_into() step_into() rechecks d_seq and __follow_mount_rcu() rechecks mount_lock. An entry that gets unlinked in between causes the lookup to retry and miss. A refwalk doesn't do this. lookup_fast() takes a reference on the hashed dentry and simply accepts it. So an unlink that happens after the reference was taken isn't seen by refwalk. That's fine for a simple file. We just happened to open it before it was unlinked, no problem. For a mountpoint and specifically a locked mountpoint it very much isn't. The unlink detaches all mounts and then removes the name. Any refwalk that hasn't traversed the mounts yet simply reveals the underlying entry. It's a very narrow window but it can be hit: reads of a covered file in 60 s, 3 walkers, ~15000 unlinks no widening 27 that step + 200 us 3741 See the appended patch for a more reliable reproducer. So check the entry after step_into(). unlink(), rmdir() and rename() mark the dentry with dont_mount() before they detach the mounts and remove the dentry. So a dentry that is marked with DCACHE_CANT_MOUNT and is unhashed by the time its mounts were looked at is a name that was unlinked under the refwalk. DCACHE_CANT_MOUNT is read after the mounts were looked up and it is set before they are detached by detach_mounts(). A refwalk that missed the mounts will see DCACHE_CANT_MOUNT. Plain d_unlinked() is fine. A rename takes the dentry off its hash chain but ___d_drop() leaves d_hash.pprev set. So only __d_drop() and a rename over the dentry unhash it. The only move that flips IS_ROOT splices in a disconnected alias. That doesn't have DCACHE_CANT_MOUNT set. Add the to step_into_slowpath(). ".." and LOOKUP_DOWN may legitimately land on an unhashed directory. A refwalk that crossed onto a mount has path.mnt different from nd->path.mnt. A dentry that a filesystem dropped on its own (d_invalidate(), d_drop()) doesn't have the flag set and is treated as before. // SPDX-License-Identifier: GPL-2.0 /* * unlink_covered: unlink a file that is a mountpoint in a detached copy of * its mount, against walkers that open it through that copy. * * A is a tmpfs with the file f1 (content SECRET_F) and the plain file * MARK_A. A' is an open_tree(OPEN_TREE_CLONE) copy of A with MARK_A bound * on A'/f1, held through an O_PATH fd on its root once the tree fd is * closed. Walkers open f1 through that fd while the driver unlinks A/f1, * where nothing is mounted on it. A walker may read MARK_A or get ENOENT. * A read of SECRET_F is a hit: the name was found after its mount was * gone. The lockless walks use openat2(RESOLVE_CACHED). * * usage: unlink_covered [-t seconds] [-w walkers] */ #ifndef _GNU_SOURCE #define _GNU_SOURCE #endif #include <errno.h> #include <fcntl.h> #include <pthread.h> #include <stdatomic.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/mount.h> #include <sys/stat.h> #include <sys/syscall.h> #include <linux/openat2.h> #ifndef __NR_open_tree #define __NR_open_tree 428 #endif #ifndef __NR_move_mount #define __NR_move_mount 429 #endif #ifndef __NR_openat2 #define __NR_openat2 437 #endif #ifndef OPEN_TREE_CLONE #define OPEN_TREE_CLONE 1 #endif #ifndef OPEN_TREE_CLOEXEC #define OPEN_TREE_CLOEXEC O_CLOEXEC #endif #ifndef MOVE_MOUNT_F_EMPTY_PATH #define MOVE_MOUNT_F_EMPTY_PATH 0x00000004 #endif #define WORK "/tmp/uc" #define ADIR WORK "/A" static int duration = 60, nwalkers = 3; static atomic_int stop, writer_waiting; static pthread_rwlock_t cur_lock = PTHREAD_RWLOCK_INITIALIZER; static int cur_fd = -1; /* the root of A', -1 while there is none */ static atomic_long n_unlink, n_walk, n_mark, n_enoent, n_othe ---truncated---
References
Impacted products
Vendor Product Version
Linux Linux Version: 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe
Version: 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe
Version: 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe
Version: 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "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": "e2b10181d913b4efa3a8dc67a532f859aa5f95e0",
              "status": "affected",
              "version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe",
              "versionType": "git"
            },
            {
              "lessThan": "5f97df8ca7fadf5b53954f50073445ba193902c0",
              "status": "affected",
              "version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe",
              "versionType": "git"
            },
            {
              "lessThan": "b43ff2deef48260bfbdc0dcb520f7929bd3e4007",
              "status": "affected",
              "version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe",
              "versionType": "git"
            },
            {
              "lessThan": "8189ab688f5a2c745dc90b63374da02f213d6994",
              "status": "affected",
              "version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe",
              "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": "3.18"
            },
            {
              "lessThan": "3.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.113",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.57",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.11",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.113",
                  "versionStartIncluding": "3.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.57",
                  "versionStartIncluding": "3.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.11",
                  "versionStartIncluding": "3.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "3.18",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamei: don\u0027t reveal overmounted entries in refwalk\n\nIn rcuwalk the dentry is validated before it is accepted. step_into()\nstep_into() rechecks d_seq and __follow_mount_rcu() rechecks mount_lock.\nAn entry that gets unlinked in between causes the lookup to retry and\nmiss.\n\nA refwalk doesn\u0027t do this. lookup_fast() takes a reference on the hashed\ndentry and simply accepts it. So an unlink that happens after the\nreference was taken isn\u0027t seen by refwalk. That\u0027s fine for a simple\nfile. We just happened to open it before it was unlinked, no problem.\n\nFor a mountpoint and specifically a locked mountpoint it very much\nisn\u0027t. The unlink detaches all mounts and then removes the name. Any\nrefwalk that hasn\u0027t traversed the mounts yet simply reveals the\nunderlying entry. It\u0027s a very narrow window but it can be hit:\n\n  reads of a covered file in 60 s, 3 walkers, ~15000 unlinks\n    no widening            27\n    that step + 200 us   3741\n\nSee the appended patch for a more reliable reproducer.\n\nSo check the entry after step_into(). unlink(), rmdir() and rename()\nmark the dentry with dont_mount() before they detach the mounts and\nremove the dentry.\n\nSo a dentry that is marked with DCACHE_CANT_MOUNT and is unhashed by the\ntime its mounts were looked at is a name that was unlinked under the\nrefwalk. DCACHE_CANT_MOUNT is read after the mounts were looked up and\nit is set before they are detached by detach_mounts(). A refwalk that\nmissed the mounts will see DCACHE_CANT_MOUNT.\n\nPlain d_unlinked() is fine. A rename takes the dentry off its hash chain\nbut ___d_drop() leaves d_hash.pprev set. So only __d_drop() and a rename\nover the dentry unhash it. The only move that flips IS_ROOT splices in a\ndisconnected alias. That doesn\u0027t have DCACHE_CANT_MOUNT set.\n\nAdd the to step_into_slowpath(). \"..\" and LOOKUP_DOWN may legitimately\nland on an unhashed directory. A refwalk that crossed onto a mount has\npath.mnt different from nd-\u003epath.mnt. A dentry that a filesystem dropped\non its own (d_invalidate(), d_drop()) doesn\u0027t have the flag set and is\ntreated as before.\n\n  // SPDX-License-Identifier: GPL-2.0\n  /*\n   * unlink_covered: unlink a file that is a mountpoint in a detached copy of\n   * its mount, against walkers that open it through that copy.\n   *\n   * A is a tmpfs with the file f1 (content SECRET_F) and the plain file\n   * MARK_A. A\u0027 is an open_tree(OPEN_TREE_CLONE) copy of A with MARK_A bound\n   * on A\u0027/f1, held through an O_PATH fd on its root once the tree fd is\n   * closed. Walkers open f1 through that fd while the driver unlinks A/f1,\n   * where nothing is mounted on it. A walker may read MARK_A or get ENOENT.\n   * A read of SECRET_F is a hit: the name was found after its mount was\n   * gone. The lockless walks use openat2(RESOLVE_CACHED).\n   *\n   * usage: unlink_covered [-t seconds] [-w walkers]\n   */\n  #ifndef _GNU_SOURCE\n  #define _GNU_SOURCE\n  #endif\n  #include \u003cerrno.h\u003e\n  #include \u003cfcntl.h\u003e\n  #include \u003cpthread.h\u003e\n  #include \u003cstdatomic.h\u003e\n  #include \u003cstdio.h\u003e\n  #include \u003cstdlib.h\u003e\n  #include \u003cstring.h\u003e\n  #include \u003cunistd.h\u003e\n  #include \u003csys/mount.h\u003e\n  #include \u003csys/stat.h\u003e\n  #include \u003csys/syscall.h\u003e\n  #include \u003clinux/openat2.h\u003e\n\n  #ifndef __NR_open_tree\n  #define __NR_open_tree 428\n  #endif\n  #ifndef __NR_move_mount\n  #define __NR_move_mount 429\n  #endif\n  #ifndef __NR_openat2\n  #define __NR_openat2 437\n  #endif\n  #ifndef OPEN_TREE_CLONE\n  #define OPEN_TREE_CLONE 1\n  #endif\n  #ifndef OPEN_TREE_CLOEXEC\n  #define OPEN_TREE_CLOEXEC O_CLOEXEC\n  #endif\n  #ifndef MOVE_MOUNT_F_EMPTY_PATH\n  #define MOVE_MOUNT_F_EMPTY_PATH 0x00000004\n  #endif\n\n  #define WORK \"/tmp/uc\"\n  #define ADIR WORK \"/A\"\n\n  static int duration = 60, nwalkers = 3;\n  static atomic_int stop, writer_waiting;\n  static pthread_rwlock_t cur_lock = PTHREAD_RWLOCK_INITIALIZER;\n  static int cur_fd = -1;\t\t/* the root of A\u0027, -1 while there is none */\n  static atomic_long n_unlink, n_walk, n_mark, n_enoent, n_othe\n---truncated---"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - Local openat/openat2 reaches do_file_open()-\u003epath_openat()-\u003elookup_fast()-\u003estep_into_slowpath(), the function patched here, while concurrent unlinkat/rmdir/renameat2 reaches detach_mounts(). No network protocol carries the trigger.\nAC:L - Attacker threads control both sides: one retains the dentry in lookup_fast() while another calls dont_mount()/detach_mounts() through unlink or rename. The reproducer repeatedly creates this race and obtained disclosures without artificial widening.\nPR:L - may_delete_dentry() requires only MAY_WRITE|MAY_EXEC on the parent, and opening uses ordinary inode permissions. Required mount setup is also available to an ordinary user through a user namespace because tmpfs has FS_USERNS_MOUNT and may_mount() checks the mount namespace\u0027s user_ns.\nUI:N - The attacker performs the mount setup, concurrent unlink or rename, and openat/openat2 attempts through their own processes; no victim must mount, open, or approve anything.\nS:C - lock_mnt_tree() applies MNT_LOCKED specifically to stop an unprivileged child user/mount namespace from revealing objects beneath inherited mounts. Accepting the underlying dentry in step_into_slowpath() crosses that mount-namespace sandbox boundary.\nC:H - After lookup_fast() retains the covered dentry and handle_mounts() misses the detached cover, vulnerable step_into_slowpath() accepts the underlying inode. The reproducer reads the complete SECRET_F contents instead of mounted MARK_A, permitting full disclosure of a covered sensitive file.\nI:H - The same exposed inode reaches do_open()-\u003emay_open(); O_WRONLY/O_RDWR permits writes when underlying DAC allows them, and O_TRUNC invokes handle_truncate(). This bypasses a locked or read-only covering mount and allows complete modification of a protected writable file.\nA:H - Opening the wrongly uncovered inode with O_TRUNC reaches handle_truncate() and can empty a covered executable, configuration, database, or other availability-critical file that the locked mount was protecting, causing complete loss of the dependent service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-24T14:09:48.534Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/e2b10181d913b4efa3a8dc67a532f859aa5f95e0"
        },
        {
          "url": "https://git.kernel.org/stable/c/5f97df8ca7fadf5b53954f50073445ba193902c0"
        },
        {
          "url": "https://git.kernel.org/stable/c/b43ff2deef48260bfbdc0dcb520f7929bd3e4007"
        },
        {
          "url": "https://git.kernel.org/stable/c/8189ab688f5a2c745dc90b63374da02f213d6994"
        }
      ],
      "title": "namei: don\u0027t reveal overmounted entries in refwalk",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98980",
    "datePublished": "2026-10-23T12:19:53.838Z",
    "dateReserved": "2026-09-25T10:25:14.383Z",
    "dateUpdated": "2026-10-24T14:09:48.534Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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