{"id":"CVE-2026-74483","summary":"binfmt_misc: don't leak the user namespace when the mount fails","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nbinfmt_misc: don't leak the user namespace when the mount fails\n\nbm_get_tree() takes a reference to the user namespace and hands it to\nget_tree_keyed() as the sget key. sget_fc() moves that reference into\nsb-\u003es_fs_info and clears fc-\u003es_fs_info, so from that point on the\nsuperblock owns it and bm_free() doesn't see it anymore.\n\nThe superblock drops it in -\u003eput_super(). But generic_shutdown_super()\nonly calls -\u003eput_super() from inside the if (sb-\u003es_root) branch, so\nnothing releases it when bm_fill_super() fails:\n\n- The kzalloc_obj() failure leaves s_root NULL and the whole branch is\n  skipped.\n\n- A simple_fill_super() failure in the file loop leaves s_root set, but\n  s_op still points at simple_super_operations, which has no\n  -\u003eput_super(). bm_fill_super() installs s_ops only once\n  simple_fill_super() returned success, and installing it earlier\n  wouldn't help either because simple_fill_super() overwrites s_op.\n\nEither way vfs_get_super() calls deactivate_locked_super() and the\nreference is gone for good. binfmt_misc mounts are available in a user\nnamespace and both the inode and the dentry cache are SLAB_ACCOUNT, so\nan unprivileged caller under a tight memory cgroup can fail\nsimple_fill_super() on demand and leak one user namespace per attempt.\n\nDrop the reference in -\u003ekill_sb() instead, which runs unconditionally,\nthe same way nfsd and rpc_pipefs release their keyed s_fs_info.\n\nThat also stops -\u003eput_super() from clearing s_fs_info while the\nsuperblock is still on @fs_supers. generic_shutdown_super() leaves it\nthere on purpose so that sget_fc() keeps finding it until kill_sb() has\nrun, but a NULL s_fs_info makes test_keyed_super() miss it, so a\nconcurrent mount for the same user namespace skips the grab_super()\nwait and creates a second superblock for a namespace that is still\nbeing torn down.","modified":"2026-08-18T03:30:52.015832974Z","published":"2026-08-15T12:27:15.709Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74483.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/87a4eb9bbb3497f749bbac612af22ddaa62d7b0d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b8206f516fe7cbe785cf44bf09c17c438d7c3cad"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74483.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-74483"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"21ca59b365c091d583f36ac753eaa8baf947be6f"},{"fixed":"87a4eb9bbb3497f749bbac612af22ddaa62d7b0d"},{"fixed":"b8206f516fe7cbe785cf44bf09c17c438d7c3cad"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74483.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"7.1.8"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74483.json"}}],"schema_version":"1.9.0"}