{"id":"CVE-2026-98980","title":"namei: don't reveal overmounted entries in refwalk","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamei: don't 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_…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe < e2b10181d913b4efa3a8dc67a532f859aa5f95e0","Linux >= 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe < 5f97df8ca7fadf5b53954f50073445ba193902c0","Linux >= 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe < b43ff2deef48260bfbdc0dcb520f7929bd3e4007","Linux >= 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe < 8189ab688f5a2c745dc90b63374da02f213d6994","Linux 3.18"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T12:19:53.838Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98980","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"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T13:24:55.549Z","slug":"CVE-2026-98980","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnamei: don't 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't 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't seen by refwalk. That's 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't. The unlink detaches all mounts and then removes the name. Any\nrefwalk that hasn't traversed the mounts yet simply reveals the\nunderlying entry. It's 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't 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->path.mnt. A dentry that a filesystem dropped\non its own (d_invalidate(), d_drop()) doesn't 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' is an open_tree(OPEN_TREE_CLONE) copy of A with MARK_A bound\n   * on A'/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 <errno.h>\n  #include <fcntl.h>\n  #include <pthread.h>\n  #include <stdatomic.h>\n  #include <stdio.h>\n  #include <stdlib.h>\n  #include <string.h>\n  #include <unistd.h>\n  #include <sys/mount.h>\n  #include <sys/stat.h>\n  #include <sys/syscall.h>\n  #include <linux/openat2.h>\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', -1 while there is none */\n  static atomic_long n_unlink, n_walk, n_mark, n_enoent, n_othe\n---truncated---\n\n## Affected\n\n- `Linux >= 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe < e2b10181d913b4efa3a8dc67a532f859aa5f95e0`\n- `Linux >= 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe < 5f97df8ca7fadf5b53954f50073445ba193902c0`\n- `Linux >= 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe < b43ff2deef48260bfbdc0dcb520f7929bd3e4007`\n- `Linux >= 8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe < 8189ab688f5a2c745dc90b63374da02f213d6994`\n- `Linux 3.18`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}