{ "affected": [ { "ranges": [ { "events": [ { "introduced": "8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe" }, { "fixed": "b3fa3811ffffa130586c4ff8f7299b7fc69216d5" }, { "fixed": "97cc290c57ea04337fd33912d780367add41525c" }, { "fixed": "bb917ec497f6099c6cb9375596e085a5f6b52ff2" }, { "fixed": "db90eecbde319527aa9480c039d32a0f5fe80574" }, { "fixed": "8d71bfc9b3fc15d7103e82ea9dc5057541866e46" }, { "fixed": "d29cd99db3db74cf3447be74d25740981789d461" }, { "fixed": "8300de4aa5d09061bfcf2af5b52c0cdba3873185" }, { "fixed": "528b383dc35d1e5caf64ddf5d35f983ae543b0d0" } ], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "type": "GIT" } ] }, { "package": { "ecosystem": "Linux", "name": "Kernel" }, "ranges": [ { "events": [ { "introduced": "3.18.0" }, { "fixed": "5.10.273" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "5.11.0" }, { "fixed": "5.15.224" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "5.16.0" }, { "fixed": "6.1.191" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.2.0" }, { "fixed": "6.6.160" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.7.0" }, { "fixed": "6.12.114" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.13.0" }, { "fixed": "6.18.57" } ], "type": "ECOSYSTEM" }, { "events": [ { "introduced": "6.19.0" }, { "fixed": "7.2.11" } ], "type": "ECOSYSTEM" } ] } ], "database_specific": { "cna_assigner": "Linux", "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98981.json" }, "details": "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 \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', -1 wh\n---truncated---", "id": "CVE-2026-98981", "modified": "2026-11-01T02:30:55.512302303Z", "published": "2026-10-23T12:19:58.507Z", "references": [ { "type": "WEB", "url": "https://git.kernel.org/stable/c/528b383dc35d1e5caf64ddf5d35f983ae543b0d0" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/8300de4aa5d09061bfcf2af5b52c0cdba3873185" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/8d71bfc9b3fc15d7103e82ea9dc5057541866e46" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/97cc290c57ea04337fd33912d780367add41525c" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/b3fa3811ffffa130586c4ff8f7299b7fc69216d5" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/bb917ec497f6099c6cb9375596e085a5f6b52ff2" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/d29cd99db3db74cf3447be74d25740981789d461" }, { "type": "WEB", "url": "https://git.kernel.org/stable/c/db90eecbde319527aa9480c039d32a0f5fe80574" }, { "type": "ADVISORY", "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98981.json" }, { "type": "ADVISORY", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98981" }, { "type": "PACKAGE", "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git" } ], "schema_version": "1.9.2", "severity": [ { "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H", "type": "CVSS_V3" } ], "summary": "namespace: unhash a dentry before detaching the mounts on it" }