setresuid allows the euid to be set to any of uid, euid, suid, and fsuid. Therefor it is safe to allow an unprivileged user to map their euid and use CAP_SETUID privileged with exactly that uid, as no new credentials can be obtained.
I can not find a combination of existing system calls that allows setting uid, euid, suid, and fsuid from the fsuid making the previous use of fsuid for allowing unprivileged mappings a bug. This is part of a fix for CVE-2014-8989. Cc: [email protected] Reviewed-by: Andy Lutomirski <[email protected]> Signed-off-by: "Eric W. Biederman" <[email protected]> --- kernel/user_namespace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 1ce6d67c07b7..9451b12a9b6c 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -819,7 +819,7 @@ static bool new_idmap_permitted(const struct file *file, u32 id = new_map->extent[0].lower_first; if (cap_setid == CAP_SETUID) { kuid_t uid = make_kuid(ns->parent, id); - if (uid_eq(uid, file->f_cred->fsuid)) + if (uid_eq(uid, file->f_cred->euid)) return true; } } -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
