{"schema":"threatline.record/2","record":{"id":"CVE-2026-98980","aliases":[],"summary":"namei: don't reveal overmounted entries in refwalk","details":"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_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---","categories":["Operating systems"],"product":"Linux","vendor":"Linux","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-98980","source_modified_at":"2026-10-23T12:19:53.838Z","fetched_at":"2026-10-23T18:42:43.628194Z","product":"Linux","vendor":"Linux","versions":[{"version":"8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe","lessThan":"e2b10181d913b4efa3a8dc67a532f859aa5f95e0","status":"affected","versionType":"git"},{"version":"8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe","lessThan":"5f97df8ca7fadf5b53954f50073445ba193902c0","status":"affected","versionType":"git"},{"version":"8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe","lessThan":"b43ff2deef48260bfbdc0dcb520f7929bd3e4007","status":"affected","versionType":"git"},{"version":"8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe","lessThan":"8189ab688f5a2c745dc90b63374da02f213d6994","status":"affected","versionType":"git"}],"defaultStatus":"unaffected"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-98980","source_modified_at":"2026-10-23T12:19:53.838Z","fetched_at":"2026-10-23T18:42:43.628194Z","product":"Linux","vendor":"Linux","versions":[{"version":"3.18","status":"affected"},{"version":"0","lessThan":"3.18","status":"unaffected","versionType":"semver"},{"version":"6.12.113","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.18.57","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.2.11","lessThanOrEqual":"7.2.*","status":"unaffected","versionType":"semver"},{"version":"7.3","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}],"defaultStatus":"affected"}],"fixed_versions":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-98980","source_modified_at":"2026-10-23T12:19:53.838Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"name":"Linux","ecosystem":null},"version":"5f97df8ca7fadf5b53954f50073445ba193902c0","basis":"first unaffected version stated in the CVE record"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-98980","source_modified_at":"2026-10-23T12:19:53.838Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"name":"Linux","ecosystem":null},"version":"8189ab688f5a2c745dc90b63374da02f213d6994","basis":"first unaffected version stated in the CVE record"}],"cvss":null,"severity":null,"kev":{"listed":false},"epss":{"probability":null,"percentile":null,"score_date":null},"published_at":"2026-10-23T12:19:53.838Z","modified_at":"2026-10-23T12:19:53.838Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-98980","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23T12:19:53.838Z"}],"sources":["CVE List"],"references":[{"source":"CVE List","url":"https://git.kernel.org/stable/c/e2b10181d913b4efa3a8dc67a532f859aa5f95e0"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/5f97df8ca7fadf5b53954f50073445ba193902c0"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/b43ff2deef48260bfbdc0dcb520f7929bd3e4007"},{"source":"CVE List","url":"https://git.kernel.org/stable/c/8189ab688f5a2c745dc90b63374da02f213d6994"}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":"product","confidence":"heuristic","reviewed":false},"change_timestamp":"2026-10-23T12:19:53.838Z","content_hash":"89e2f1e68660e9dce912438e2388f2db348c18a08141db0342aa365b60dee047"}}