userns,pidns: Force thread group sharing, not signal handler sharing.

The code that places signals in signal queues computes the uids, gids,
and pids at the time the signals are enqueued.  Which means that tasks
that share signal queues must be in the same pid and user namespaces.

Sharing signal handlers is fine, but bizarre.

So make the code in fork and userns_install clearer by only testing
for what is functionally necessary.

Also update the comment in unshare about unsharing a user namespace to
be a little more explicit and make a little more sense.

Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/kernel/fork.c b/kernel/fork.c
index d544ae97f999f04fafeef9ff80018124873221ec..2c72b8a8ae24947418fd359d308f685a9f6d5946 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1273,10 +1273,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 
        /*
         * If the new process will be in a different pid or user namespace
-        * do not allow it to share a thread group or signal handlers or
-        * parent with the forking task.
+        * do not allow it to share a thread group with the forking task.
         */
-       if (clone_flags & CLONE_SIGHAND) {
+       if (clone_flags & CLONE_THREAD) {
                if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
                    (task_active_pid_ns(current) !=
                                current->nsproxy->pid_ns_for_children))
@@ -1944,7 +1943,8 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
        int err;
 
        /*
-        * If unsharing a user namespace must also unshare the thread.
+        * If unsharing a user namespace must also unshare the thread group
+        * and unshare the filesystem root and working directories.
         */
        if (unshare_flags & CLONE_NEWUSER)
                unshare_flags |= CLONE_THREAD | CLONE_FS;

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 4109f8320684a81af4cd9d0c7262f83812c300f2..f65a0a06a8c067726b76a37418c80919cf59c4d7 100644 (file)
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -976,8 +976,8 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
        if (user_ns == current_user_ns())
                return -EINVAL;
 
-       /* Threaded processes may not enter a different user namespace */
-       if (atomic_read(&current->mm->mm_users) > 1)
+       /* Tasks that share a thread group must share a user namespace */
+       if (!thread_group_empty(current))
                return -EINVAL;
 
        if (current->fs->users != 1)