{"id":"CVE-2026-74619","summary":"ovl: don't warn when the mount is completed from another user namespace","details":"In the Linux kernel, the following vulnerability has been resolved:\n\novl: don't warn when the mount is completed from another user namespace\n\nfsopen() records the caller's user namespace in fc-\u003euser_ns and hands\nback an ordinary file descriptor. Nothing ties the task that calls\nfsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The\nfd is inherited across fork() and exec() and it can be passed over a\nunix socket.\n\nCompleting a context from another user namespace is allowed on purpose.\nvfs_cmd_create() authorizes the create with mount_capable(), which for\nFS_USERNS_MOUNT checks ns_capable(fc-\u003euser_ns, CAP_SYS_ADMIN), and that\nsucceeds for a task holding CAP_SYS_ADMIN in an ancestor of fc-\u003euser_ns.\nSo an unprivileged task can reach the WARN_ON() in ovl_fill_super():\ncreate a user and a mount namespace in a child, call fsopen(\"overlay\")\nthere, send the fscontext fd to the parent and let the parent issue\nFSCONFIG_CMD_CREATE. Both namespaces come from a plain unshare(1) and no\ncapability is needed anywhere:\n\n  WARNING: fs/overlayfs/super.c:1551 at ovl_fill_super+0x7b9/0x1e20 [overlay]\n  CPU: 3 UID: 1000 PID: 3243376 Comm: fswarn\n  Call Trace:\n   get_tree_nodev+0x71/0xa0\n   ovl_get_tree+0x15/0x20 [overlay]\n   vfs_get_tree+0x2a/0x100\n   vfs_cmd_create+0x60/0xf0\n   __do_sys_fsconfig+0x4b2/0x500\n\nThe child needs the mount namespace because fsopen() itself gates on\nmay_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning\nthe caller's mount namespace. fsconfig() doesn't repeat that check.\n\nIt is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be\nraised in a loop to taint the kernel and flood the log, and it panics a\nkernel booted with panic_on_warn.\n\nKeep refusing the mount and stop warning about it. ovl_parse_param()\nalready spells a user namespace check this way for Opt_override_creds.","modified":"2026-08-24T11:47:12.661483974Z","published":"2026-08-22T15:32:03.511Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74619.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/42d99fcd8006007e2f708bede6789f37f3910b30"},{"type":"WEB","url":"https://git.kernel.org/stable/c/494346f2aab2489d379d43ff614aea447cf4e94d"},{"type":"WEB","url":"https://git.kernel.org/stable/c/513478092966dc9818d96dd2b3ed613fd2f6e30e"},{"type":"WEB","url":"https://git.kernel.org/stable/c/63981fc786daaa626cb14d9be1406f674d79f98f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/be161fa31e3e9cc828a3c1bd935edca461e8a7a1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/74xxx/CVE-2026-74619.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-74619"},{"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":"1784fbc2ed9c888ea4e895f30a53207ed7ee8208"},{"fixed":"513478092966dc9818d96dd2b3ed613fd2f6e30e"},{"fixed":"494346f2aab2489d379d43ff614aea447cf4e94d"},{"fixed":"be161fa31e3e9cc828a3c1bd935edca461e8a7a1"},{"fixed":"42d99fcd8006007e2f708bede6789f37f3910b30"},{"fixed":"63981fc786daaa626cb14d9be1406f674d79f98f"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74619.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"6.5.0"},{"fixed":"6.6.152"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.104"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.45"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.9"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-74619.json"}}],"schema_version":"1.9.0"}