GHSA-R8CP-FX7R-5FXQ
Vulnerability from github – Published: 2026-10-23 15:31 – Updated: 2026-10-23 15:31In 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 #include #include #include #include #include #include #include #include #include #include #include
#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---
{
"affected": [],
"aliases": [
"CVE-2026-98980"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-10-23T13:17:19Z",
"severity": null
},
"details": "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---",
"id": "GHSA-r8cp-fx7r-5fxq",
"modified": "2026-10-23T15:31:33Z",
"published": "2026-10-23T15:31:33Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98980"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5f97df8ca7fadf5b53954f50073445ba193902c0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8189ab688f5a2c745dc90b63374da02f213d6994"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b43ff2deef48260bfbdc0dcb520f7929bd3e4007"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e2b10181d913b4efa3a8dc67a532f859aa5f95e0"
}
],
"schema_version": "1.4.0",
"severity": []
}
Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
Loading timeline…
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.