{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-98981", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-25T10:25:14.384Z", "datePublished": "2026-10-23T12:19:58.507Z", "dateUpdated": "2026-10-24T14:09:49.642Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-24T14:09:49.642Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: unhash a dentry before detaching the mounts on it\n\nunlink(), rmdir() and rename() remove the entry from the filesystem,\ncall detach_mounts() on the entry with the inode locked and then call\nd_delete() once the inode is unlocked.\n\nThe thing is that between detach_mounts() and d_delete() the dentry is\nstill hashed and positive. But after detach_mounts() nothing covers the\ndentry anymore. A lookup that finds this dentry in the dcache can\nuncover what the mounts hid.\n\nThat's a problem when unlinking files or directories that are\nmountpoints in other mount namespaces. Everybody who had the underlying\nentry covered can race the detach_mount() call until d_delete() has run.\n\nThe race window isn't all that small. It encompasses namespace_unlock()\nwith a full synchronize_rcu_expedited() grace period and the\ninode_unlock() of the entry.\n\nIn my experiments three walkers that kept trying read an overmounted\nfile in 11938 of the 16140 unlinks that removed its mountpoint from a\nbind mount of the filesystem within a minute.\n\nFun fact, d_invalidate() has the same ordering problem but gets it\nright. It unhashes the dentry first and detaches the mounts afterwards.\nLet's do the same in __detach_mounts():\n\n- A lookup that hasn't found the dentry yet misses it in the dcache and\n waits for the directory lock that the caller holds until the name is\n gone for good.\n\n- A lockless lookup that found it already fails the mount_lock check\n while the dentry still counts as a mountpoint and the d_seq check once\n it doesn't, and retries.\n\nThis fixes the lockless path. We still need to fix the reference count\nlookup in a follow-up patch.\n\nSo d_drop() the dentry. The dentry stays positive and held but can't be\nfound anymore. Then proceed with the detach and unlink.\n\nReproducer:\n\nThe reads were counted with the program below, three walkers for 60 s\nin a VM with 4 CPUs. The race window is stretched with the debug patch\npasted here. fs.detach_race_walk_us sleeps in lookup_fast() once it\nfound a mountpoint dentry and before its mounts are crossed.\nfs.detach_race_unlink_us sleeps in vfs_unlink() between detach_mounts()\nand d_delete().\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 lookups 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 \n #include \n #include \n #include \n #include \n #include \n #include \n #include \n #include \n #include \n #include \n #include \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 wh\n---truncated---" } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H", "baseScore": 8.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The trigger uses local unlinkat(), rmdir(), or renameat2() into vfs_unlink(), vfs_rmdir(), or vfs_rename(), which call the patched __detach_mounts(), while a concurrent openat2() path walk races the detach; no network data reaches this path.\nAC:L - The attacker controls both sides by unlinking the underlying entry while concurrent lookup_fast() walkers open it through the covered mount; the reproducer obtained 11,938 disclosures in 16,140 unlinks.\nPR:L - may_delete_dentry() requires ordinary write and execute permission on the parent, while may_mount() uses CAP_SYS_ADMIN in the mount namespace's user namespace; an unprivileged user can obtain that capability with a new user/mount namespace and mount tmpfs because it has FS_USERNS_MOUNT.\nUI:N - The attacker creates the mount arrangement and directly drives both the removal syscall and concurrent openat2() calls; no separate victim action is required.\nS:C - __detach_mounts() removes mounts attached to the shared dentry across namespaces, allowing a walk in the covered A' namespace to reach the underlying A object. This crosses the mount-namespace isolation boundary the covering mount enforced.\nC:H - The stale positive dentry accepted by lookup_fast() and step_into() can be opened and read after its covering mount disappears; the reproducer reads the complete SECRET_F contents rather than a bounded metadata fragment.\nI:H - The incorrectly uncovered dentry proceeds to do_open(), where may_open() permits O_WRONLY under normal inode permissions and O_TRUNC reaches handle_truncate(); thus a mount-hidden writable object, or the target of an uncovered symlink, can be modified or erased.\nA:H - A stale covered symlink can reach pick_link() and resolve a persistent target, after which do_open() can invoke handle_truncate() for O_TRUNC. Erasing a mount-hidden critical file can cause complete loss of the dependent resource or service." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/namespace.c" ], "versions": [ { "version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe", "lessThan": "db90eecbde319527aa9480c039d32a0f5fe80574", "status": "affected", "versionType": "git" }, { "version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe", "lessThan": "8d71bfc9b3fc15d7103e82ea9dc5057541866e46", "status": "affected", "versionType": "git" }, { "version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe", "lessThan": "d29cd99db3db74cf3447be74d25740981789d461", "status": "affected", "versionType": "git" }, { "version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe", "lessThan": "8300de4aa5d09061bfcf2af5b52c0cdba3873185", "status": "affected", "versionType": "git" }, { "version": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe", "lessThan": "528b383dc35d1e5caf64ddf5d35f983ae543b0d0", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/namespace.c" ], "versions": [ { "version": "3.18", "status": "affected" }, { "version": "0", "lessThan": "3.18", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.160", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.114", "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" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.18", "versionEndExcluding": "6.6.160" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.18", "versionEndExcluding": "6.12.114" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.18", "versionEndExcluding": "6.18.57" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.18", "versionEndExcluding": "7.2.11" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.18", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/db90eecbde319527aa9480c039d32a0f5fe80574" }, { "url": "https://git.kernel.org/stable/c/8d71bfc9b3fc15d7103e82ea9dc5057541866e46" }, { "url": "https://git.kernel.org/stable/c/d29cd99db3db74cf3447be74d25740981789d461" }, { "url": "https://git.kernel.org/stable/c/8300de4aa5d09061bfcf2af5b52c0cdba3873185" }, { "url": "https://git.kernel.org/stable/c/528b383dc35d1e5caf64ddf5d35f983ae543b0d0" } ], "title": "namespace: unhash a dentry before detaching the mounts on it", "x_generator": { "engine": "bippy-1.2.0" } } } }