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>

1 files changed, 4 insertions, 4 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index d544ae97f999..2c72b8a8ae24 100644
--- 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;