{"id":"DEBIAN-CVE-2026-98980","details":"In 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-\u003epath.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 \u003cerrno.h\u003e   #include \u003cfcntl.h\u003e   #include \u003cpthread.h\u003e   #include \u003cstdatomic.h\u003e   #include \u003cstdio.h\u003e   #include \u003cstdlib.h\u003e   #include \u003cstring.h\u003e   #include \u003cunistd.h\u003e   #include \u003csys/mount.h\u003e   #include \u003csys/stat.h\u003e   #include \u003csys/syscall.h\u003e   #include \u003clinux/openat2.h\u003e    #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;\t\t/* the root of A', -1 while there is none */   static atomic_long n_unlink, n_walk, n_mark, n_enoent, n_othe ---truncated---","modified":"2026-10-25T10:01:30.299140861Z","published":"2026-10-23T13:17:19.750Z","upstream":["CVE-2026-98980"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-98980"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["6.1.106-1","6.1.106-2","6.1.106-3","6.1.112-1","6.1.115-1","6.1.119-1","6.1.123-1","6.1.124-1","6.1.128-1","6.1.129-1","6.1.133-1","6.1.135-1","6.1.137-1","6.1.139-1","6.1.140-1","6.1.147-1","6.1.148-1","6.1.153-1","6.1.158-1","6.1.159-1","6.1.162-1","6.1.164-1","6.1.170-1","6.1.170-2","6.1.170-3","6.1.172-1","6.1.174-1","6.1.176-1","6.1.177-1","6.1.180-1","6.1.187-1","6.1.190-1","6.1.27-1","6.1.37-1","6.1.38-1","6.1.38-2","6.1.38-2~bpo11+1","6.1.38-3","6.1.38-4","6.1.38-4~bpo11+1","6.1.52-1","6.1.55-1","6.1.55-1~bpo11+1","6.1.64-1","6.1.66-1","6.1.67-1","6.1.69-1","6.1.69-1~bpo11+1","6.1.76-1","6.1.76-1~bpo11+1","6.1.82-1","6.1.85-1","6.1.90-1","6.1.90-1~bpo11+1","6.1.94-1","6.1.94-1~bpo11+1","6.1.98-1","6.1.99-1","6.10-1~exp1","6.10.1-1~exp1","6.10.11-1","6.10.11-1~bpo12+1","6.10.12-1","6.10.3-1","6.10.4-1","6.10.6-1","6.10.6-1~bpo12+1","6.10.7-1","6.10.9-1","6.11-1~exp1","6.11.10-1","6.11.10-1~bpo12+1","6.11.2-1","6.11.4-1","6.11.5-1","6.11.5-1~bpo12+1","6.11.6-1","6.11.7-1","6.11.9-1","6.11~rc4-1~exp1","6.11~rc5-1~exp1","6.12.10-1","6.12.100-1","6.12.101-1","6.12.105-1","6.12.107-1","6.12.11-1","6.12.11-1+alpha","6.12.11-1+alpha.1","6.12.111-1","6.12.113-1","6.12.12-1","6.12.12-1~bpo12+1","6.12.13-1","6.12.15-1","6.12.16-1","6.12.17-1","6.12.19-1","6.12.20-1","6.12.21-1","6.12.22-1","6.12.22-1~bpo12+1","6.12.25-1","6.12.27-1","6.12.27-1~bpo12+1","6.12.29-1","6.12.3-1","6.12.30-1","6.12.30-1~bpo12+1","6.12.31-1","6.12.32-1","6.12.32-1~bpo12+1","6.12.33-1","6.12.33-1~bpo12+1","6.12.35-1","6.12.35-1~bpo12+1","6.12.37-1","6.12.38-1","6.12.38-1~bpo12+1","6.12.41-1","6.12.43-1","6.12.43-1~bpo12+1","6.12.48-1","6.12.5-1","6.12.57-1","6.12.57-1~bpo12+1","6.12.6-1","6.12.63-1","6.12.63-1~bpo12+1","6.12.69-1","6.12.69-1~bpo12+1","6.12.73-1","6.12.73-1~bpo12+1","6.12.74-1","6.12.74-2","6.12.74-2~bpo12+1","6.12.8-1","6.12.85-1","6.12.85-1~bpo12+1","6.12.86-1","6.12.86-1~bpo12+1","6.12.88-1","6.12.88-1~bpo12+1","6.12.9-1","6.12.9-1+alpha","6.12.9-1~bpo12+1","6.12.90-1","6.12.90-1~bpo12+1","6.12.90-2","6.12.90-2~bpo12+1","6.12.94-1","6.12.94-1~bpo12+1","6.12.95-1","6.12.95-1~bpo12+1","6.12.96-1","6.12~rc6-1~exp1","6.13.10-1~exp1","6.13.11-1~exp1","6.13.2-1~exp1","6.13.3-1~exp1","6.13.4-1~exp1","6.13.5-1~exp1","6.13.6-1~exp1","6.13.7-1~exp1","6.13.8-1~exp1","6.13.9-1~exp1","6.13~rc6-1~exp1","6.13~rc7-1~exp1","6.14.3-1~exp1","6.14.5-1~exp1","6.14.6-1~exp1","6.15-1~exp1","6.15.1-1~exp1","6.15.2-1~exp1","6.15.3-1~exp1","6.15.4-1~exp1","6.15.5-1~exp1","6.15.6-1~exp1","6.15~rc7-1~exp1","6.16-1~exp1","6.16.1-1~exp1","6.16.10-1","6.16.11-1","6.16.12-1","6.16.12-1~bpo13+1","6.16.12-2","6.16.3-1","6.16.3-1~bpo13+1","6.16.5-1","6.16.6-1","6.16.7-1","6.16.8-1","6.16.9-1","6.16~rc7-1~exp1","6.17.10-1","6.17.11-1","6.17.12-1","6.17.13-1","6.17.13-1~bpo13+1","6.17.2-1~exp1","6.17.5-1~exp1","6.17.6-1","6.17.7-1","6.17.7-2","6.17.8-1","6.17.8-1~bpo13+1","6.17.9-1","6.18.1-1~exp1","6.18.10-1","6.18.12-1","6.18.12-1~bpo13+1","6.18.13-1","6.18.14-1","6.18.15-1","6.18.15-1~bpo13+1","6.18.2-1~exp1","6.18.3-1","6.18.5-1","6.18.5-1~bpo13+1","6.18.8-1","6.18.9-1","6.18.9-1~bpo13+1","6.18~rc4-1~exp1","6.18~rc4-1~exp2","6.18~rc5-1~exp1","6.18~rc6-1~exp1","6.18~rc7-1~exp1","6.19-1~exp1","6.19.10-1","6.19.10-1~bpo13+1","6.19.11-1","6.19.11-1~bpo13+1","6.19.12-1","6.19.13-1","6.19.13-1~bpo13+1","6.19.14-1","6.19.14-1~bpo13+1","6.19.2-1~exp1","6.19.3-1~exp1","6.19.4-1~exp1","6.19.5-1~exp1","6.19.6-1","6.19.6-2","6.19.6-2~bpo13+1","6.19.8-1","6.19.8-1~bpo13+1","6.19~rc4-1~exp1","6.19~rc5-1~exp1","6.19~rc6-1~exp1","6.19~rc7-1~exp1","6.19~rc8-1~exp1","6.3.1-1~exp1","6.3.11-1","6.3.2-1~exp1","6.3.4-1~exp1","6.3.5-1~exp1","6.3.7-1","6.3.7-1~bpo12+1","6.4.1-1~exp1","6.4.11-1","6.4.13-1","6.4.4-1","6.4.4-1~bpo12+1","6.4.4-2","6.4.4-3","6.4.4-3~bpo12+1","6.4~rc6-1~exp1","6.4~rc7-1~exp1","6.5.1-1~exp1","6.5.10-1","6.5.10-1~bpo12+1","6.5.13-1","6.5.3-1","6.5.3-1~bpo12+1","6.5.6-1","6.5.8-1","6.5~rc4-1~exp1","6.5~rc6-1~exp1","6.5~rc7-1~exp1","6.6.11-1","6.6.13-1","6.6.13-1~bpo12+1","6.6.15-1","6.6.15-2","6.6.3-1~exp1","6.6.4-1~exp1","6.6.7-1~exp1","6.6.8-1","6.6.9-1","6.7-1~exp1","6.7.1-1~exp1","6.7.12-1","6.7.12-1~bpo12+1","6.7.4-1~exp1","6.7.7-1","6.7.9-1","6.7.9-2","6.8.11-1","6.8.12-1","6.8.12-1~bpo12+1","6.8.9-1","6.9.10-1","6.9.10-1~bpo12+1","6.9.11-1","6.9.12-1","6.9.2-1~exp1","6.9.7-1","6.9.7-1~bpo12+1","6.9.8-1","6.9.9-1","7.0-1~exp1","7.0.1-1~exp1","7.0.10-1","7.0.10-1~bpo13+1","7.0.12-1","7.0.12-2","7.0.12-2~bpo13+1","7.0.13-1","7.0.13-1~bpo13+1","7.0.14-1","7.0.3-1","7.0.4-1","7.0.4-1~bpo13+1","7.0.7-1","7.0.7-1~bpo13+1","7.0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