namespaces && fork fixes/cleanups

Hello.

To remind, 1/3 fixes the regression, perhaps it should cc -stable.

v2:
changed the comment, added the acks from Andy.

Still needs the review from Eric.

Oleg.

 kernel/fork.c |   22 ++++++++--------------
 1 files changed, 8 insertions(+), 14 deletions(-)

8382fcac "pidns: Outlaw thread creation after unshare(CLONE_NEWPID)" nacks CLONE_VM if the forking process unshared pid_ns, this obviously breaks vfork:

	int main(void)
	{
		assert(unshare(CLONE_NEWUSER | CLONE_NEWPID) == 0);
		assert(vfork() >= 0);
		_exit(0);
		return 0;
	}

fails without this patch.

Change this check to use CLONE_SIGHAND instead. This also forbids CLONE_THREAD automatically, and this is what the comment implies.

We could probably even drop CLONE_SIGHAND and use CLONE_THREAD, but it would be safer to not do this. The current check denies CLONE_SIGHAND implicitely and there is no reason to change this.

---
 kernel/fork.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

index e23bb19..29c9f6b 100644
@@ -1173,10 +1173,11 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 		return ERR_PTR(-EINVAL);
 
 	/*
-	 * If the new process will be in a different pid namespace
-	 * don't allow the creation of threads.
+	 * If the new process will be in a different pid namespace don't
+	 * allow it to share a thread group or signal handlers with the
+	 * forking task.
 	 */
-	if ((clone_flags & (CLONE_VM|CLONE_NEWPID)) &&
+	if ((clone_flags & (CLONE_SIGHAND | CLONE_NEWPID)) &&
 	    (task_active_pid_ns(current) != current->nsproxy->pid_ns))
 		return ERR_PTR(-EINVAL);
 

1.5.5.1

8382fcac "pidns: Outlaw thread creation after unshare(CLONE_NEWPID)" nacks CLONE_NEWPID if the forking process unshared pid_ns. This is correct but unnecessary, copy_pid_ns() does the same check.

Remove the CLONE_NEWPID check to cleanup the code and prepare for the next change.

Test-case:

	static int child(void *arg)
	{
		return 0;
	}

	static char stack[16 * 1024];

	int main(void)
	{
		pid_t pid;

		assert(unshare(CLONE_NEWUSER | CLONE_NEWPID) == 0);

		pid = clone(child, stack + sizeof(stack) / 2,
				CLONE_NEWPID | SIGCHLD, NULL);
		assert(pid < 0 && errno == EINVAL);

		return 0;
	}

clone(CLONE_NEWPID) correctly fails with or without this change.

---
 kernel/fork.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 29c9f6b..27b5918 100644
@@ -1177,7 +1177,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	 * allow it to share a thread group or signal handlers with the
 	 * forking task.
 	 */
-	if ((clone_flags & (CLONE_SIGHAND | CLONE_NEWPID)) &&
+	if ((clone_flags & CLONE_SIGHAND) &&
 	    (task_active_pid_ns(current) != current->nsproxy->pid_ns))
 		return ERR_PTR(-EINVAL);
 

1.5.5.1

do_fork() denies CLONE_THREAD | CLONE_PARENT if NEWUSER | NEWPID.

Then later copy_process() denies CLONE_SIGHAND if the new process will be in a different pid namespace (task_active_pid_ns() doesn't match current->nsproxy->pid_ns).

This looks confusing and inconsistent. CLONE_NEWPID is very similar to the case when ->pid_ns was already unshared, we want the same restrictions so copy_process() should also nack CLONE_PARENT.

And it would be better to deny CLONE_NEWUSER && CLONE_SIGHAND as well just for consistency.

Kill the "CLONE_NEWUSER | CLONE_NEWPID" check in do_fork() and change copy_process() to do the same check along with ->pid_ns check we already have.

---
 kernel/fork.c |   23 ++++++++---------------
 1 files changed, 8 insertions(+), 15 deletions(-)

index 27b5918..4a23dc4 100644
@@ -1173,13 +1173,15 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 		return ERR_PTR(-EINVAL);
 
 	/*
-	 * If the new process will be in a different pid namespace don't
-	 * allow it to share a thread group or signal handlers with the
-	 * forking task.
+	 * 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.
 	 */
-	if ((clone_flags & CLONE_SIGHAND) &&
-	    (task_active_pid_ns(current) != current->nsproxy->pid_ns))
-		return ERR_PTR(-EINVAL);
+	if (clone_flags & (CLONE_SIGHAND | CLONE_PARENT)) {
+		if ((clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) ||
+		    (task_active_pid_ns(current) != current->nsproxy->pid_ns))
+			return ERR_PTR(-EINVAL);
+	}
 
 	retval = security_task_create(clone_flags);
 	if (retval)

@@ -1576,15 +1578,6 @@ long do_fork(unsigned long clone_flags,
 	long nr;
 
 	/*
-	 * Do some preliminary argument and permissions checking before we
-	 * actually start allocating stuff
-	 */
-	if (clone_flags & (CLONE_NEWUSER | CLONE_NEWPID)) {
-		if (clone_flags & (CLONE_THREAD|CLONE_PARENT))
-			return -EINVAL;
-	}
-
-	/*
 	 * Determine whether and which event to report to ptracer.  When
 	 * called from kernel_thread or CLONE_UNTRACED is explicitly
 	 * requested, no event is reported; otherwise, report if the event

1.5.5.1