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" --- fs/namespace.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'fs') diff --git a/fs/namespace.c b/fs/namespace.c index c1bbe86f492..398a50ff243 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2781,7 +2781,8 @@ static int mntns_install(struct nsproxy *nsproxy, void *ns) struct path root; if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) || - !nsown_capable(CAP_SYS_CHROOT)) + !nsown_capable(CAP_SYS_CHROOT) || + !nsown_capable(CAP_SYS_ADMIN)) return -EPERM; if (fs->users != 1) -- cgit v1.2.3-70-g09d2