From 5e4a08476b50fa39210fca82e03325cc46b9c235 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 14 Dec 2012 07:55:36 -0800 Subject: userns: Require CAP_SYS_ADMIN for most uses of setns. Andy Lutomirski found a nasty little bug in the permissions of setns. With unprivileged user namespaces it became possible to create new namespaces without privilege. However the setns calls were relaxed to only require CAP_SYS_ADMIN in the user nameapce of the targed namespace. Which made the following nasty sequence possible. pid = clone(CLONE_NEWUSER | CLONE_NEWNS); if (pid == 0) { /* child */ system("mount --bind /home/me/passwd /etc/passwd"); } else if (pid != 0) { /* parent */ char path[PATH_MAX]; snprintf(path, sizeof(path), "/proc/%u/ns/mnt"); fd = open(path, O_RDONLY); setns(fd, 0); system("su -"); } Prevent this possibility by requiring CAP_SYS_ADMIN in the current user namespace when joing all but the user namespace. Acked-by: Serge Hallyn Signed-off-by: "Eric W. Biederman" --- kernel/pid_namespace.c | 3 ++- kernel/utsname.c | 3 ++- 2 files changed, 4 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c index 560da0dab230..fdbd0cdf271a 100644 --- a/kernel/pid_namespace.c +++ b/kernel/pid_namespace.c @@ -325,7 +325,8 @@ static int pidns_install(struct nsproxy *nsproxy, void *ns) struct pid_namespace *active = task_active_pid_ns(current); struct pid_namespace *ancestor, *new = ns; - if (!ns_capable(new->user_ns, CAP_SYS_ADMIN)) + if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) || + !nsown_capable(CAP_SYS_ADMIN)) return -EPERM; /* diff --git a/kernel/utsname.c b/kernel/utsname.c index f6336d51d64c..08b197e8c485 100644 --- a/kernel/utsname.c +++ b/kernel/utsname.c @@ -113,7 +113,8 @@ static int utsns_install(struct nsproxy *nsproxy, void *new) { struct uts_namespace *ns = new; - if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) + if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) || + !nsown_capable(CAP_SYS_ADMIN)) return -EPERM; get_uts_ns(ns); -- cgit v1.2.3-59-g8ed1b