180 lines
13 KiB
JSON
180 lines
13 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2026-98980",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2026-09-25T10:25:14.383Z",
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"datePublished": "2026-10-23T12:19:53.838Z",
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"dateUpdated": "2026-10-24T14:09:48.534Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-10-24T14:09:48.534Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"value": "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---"
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
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"baseScore": 8.8,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:L - Local openat/openat2 reaches do_file_open()->path_openat()->lookup_fast()->step_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's 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()->may_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."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"fs/namei.c"
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],
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"versions": [
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{
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"version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe",
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"lessThan": "e2b10181d913b4efa3a8dc67a532f859aa5f95e0",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe",
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"lessThan": "5f97df8ca7fadf5b53954f50073445ba193902c0",
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"status": "affected",
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"versionType": "git"
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{
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"lessThan": "b43ff2deef48260bfbdc0dcb520f7929bd3e4007",
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"status": "affected",
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"lessThan": "8189ab688f5a2c745dc90b63374da02f213d6994",
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"status": "affected",
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}
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]
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},
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "affected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"fs/namei.c"
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],
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"versions": [
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{
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"version": "3.18",
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"status": "affected"
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},
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{
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"version": "0",
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"lessThan": "3.18",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.12.113",
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"lessThanOrEqual": "6.12.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.18.57",
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"lessThanOrEqual": "6.18.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.2.11",
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"lessThanOrEqual": "7.2.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.3",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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}
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]
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}
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],
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"cpeApplicability": [
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"nodes": [
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"operator": "OR",
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "3.18",
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]
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],
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"references": [
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{
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"url": "https://git.kernel.org/stable/c/e2b10181d913b4efa3a8dc67a532f859aa5f95e0"
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},
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{
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"url": "https://git.kernel.org/stable/c/5f97df8ca7fadf5b53954f50073445ba193902c0"
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},
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{
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"url": "https://git.kernel.org/stable/c/b43ff2deef48260bfbdc0dcb520f7929bd3e4007"
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},
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{
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"url": "https://git.kernel.org/stable/c/8189ab688f5a2c745dc90b63374da02f213d6994"
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}
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],
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"title": "namei: don't reveal overmounted entries in refwalk",
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"x_generator": {
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