From e66eded8309ebf679d3d3c1f5820d1f2ca332c71 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Wed, 13 Mar 2013 11:51:49 -0700 Subject: [PATCH] userns: Don't allow CLONE_NEWUSER | CLONE_FS Don't allowing sharing the root directory with processes in a different user namespace. There doesn't seem to be any point, and to allow it would require the overhead of putting a user namespace reference in fs_struct (for permission checks) and incrementing that reference count on practically every call to fork. So just perform the inexpensive test of forbidding sharing fs_struct acrosss processes in different user namespaces. We already disallow other forms of threading when unsharing a user namespace so this should be no real burden in practice. This updates setns, clone, and unshare to disallow multiple user namespaces sharing an fs_struct. Cc: stable@vger.kernel.org Signed-off-by: "Eric W. Biederman" Signed-off-by: Linus Torvalds --- kernel/fork.c | 5 ++++- kernel/user_namespace.c | 4 ++++ 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index 8d932b1c9056..1766d324d5e3 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1141,6 +1141,9 @@ static struct task_struct *copy_process(unsigned long clone_flags, if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS)) return ERR_PTR(-EINVAL); + if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS)) + return ERR_PTR(-EINVAL); + /* * Thread groups must share signals as well, and detached threads * can only be started up within the thread group. @@ -1807,7 +1810,7 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) * If unsharing a user namespace must also unshare the thread. */ if (unshare_flags & CLONE_NEWUSER) - unshare_flags |= CLONE_THREAD; + unshare_flags |= CLONE_THREAD | CLONE_FS; /* * If unsharing a pid namespace must also unshare the thread. */ diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 8b650837083e..b14f4d342043 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -21,6 +21,7 @@ #include #include #include +#include static struct kmem_cache *user_ns_cachep __read_mostly; @@ -837,6 +838,9 @@ static int userns_install(struct nsproxy *nsproxy, void *ns) if (atomic_read(¤t->mm->mm_users) > 1) return -EINVAL; + if (current->fs->users != 1) + return -EINVAL; + if (!ns_capable(user_ns, CAP_SYS_ADMIN)) return -EPERM; -- 2.20.1