{"id":"CVE-2026-98982","published":"2026-10-23T13:17:20.043","lastModified":"2026-10-24T14:16:50.850","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnamespace: don't let a pseudo dentry become the root of a mount\n\nd_alloc_pseudo() hands out dentries for pipes, sockets and other files\nthat are never anyone's child or parent. They carry DCACHE_NORCU and\ndentry_free() frees them right away because no lockless path walk can\never reach them. That holds as long as such a dentry isn't the root of\na mount. But bind mounting /proc/self/fd/<fd> of such a file does\nexactly that.\n\nMost callers of alloc_file_pseudo() put their files on kernel-internal\nmounts and may_copy_tree() refuses those. bpf_token_create() doesn't. It\nplaces the token file on the bpffs mount the caller handed it and that\nmount is in the caller's mount namespace so the clone goes through:\n\n  mount --bind /proc/self/fd/<token> <file>\n  open_tree(tokfd, \"\", AT_EMPTY_PATH | OPEN_TREE_CLONE) + move_mount()\n\n__follow_mount_rcu() then loads ->mnt_root of that mount, reads d_seq\nand d_flags of the dentry and only then checks mount_lock. The dentry\ncan be gone by then. The final mntput() of an unmounted parent unhooks\na child that stayed attached to it under mount_lock alone. When the\nchild's holder does the final put right after that the root is dput()\nand freed immediately while a walker that found the mount hashed still\nlooks at it.\n\nRefuse to clone a mount with a DCACHE_NORCU dentry as its root. Nothing\nsensible can be done with a bind mount of a bpf token anyway.","cvssScore":7.8,"cvssSeverity":"HIGH","cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cwes":[],"vendors":[],"products":[],"references":[{"url":"https://git.kernel.org/stable/c/00287afa7cd989efdbf5822b7efac33cce7d489a","tags":[]},{"url":"https://git.kernel.org/stable/c/7e1c466011ba9e64d43075396badc03191bcee44","tags":[]},{"url":"https://git.kernel.org/stable/c/a256e31e0c54c4c37d2523aa52faabdcdd2ebc07","tags":[]},{"url":"https://git.kernel.org/stable/c/b138e16fb1e81376cea89f727dda7bfccd140de4","tags":[]}],"exploitRefs":[],"hasPoc":false,"ai":null}