1 files changed, 18 insertions, 10 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 1bfefc6f96a4..d544ae97f999 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1866,13 +1866,21 @@ static int check_unshare_flags(unsigned long unshare_flags)
                                 CLONE_NEWUSER|CLONE_NEWPID))
                 return -EINVAL;
         /*
-         * Not implemented, but pretend it works if there is nothing to
-         * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND
-         * needs to unshare vm.
+         * Not implemented, but pretend it works if there is nothing
+         * to unshare.  Note that unsharing the address space or the
+         * signal handlers also need to unshare the signal queues (aka
+         * CLONE_THREAD).
          */
         if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {
-                /* FIXME: get_task_mm() increments ->mm_users */
-                if (atomic_read(&current->mm->mm_users) > 1)
+                if (!thread_group_empty(current))
+                        return -EINVAL;
+        }
+        if (unshare_flags & (CLONE_SIGHAND | CLONE_VM)) {
+                if (atomic_read(&current->sighand->count) > 1)
+                        return -EINVAL;
+        }
+        if (unshare_flags & CLONE_VM) {
+                if (!current_is_single_threaded())
                         return -EINVAL;
         }
 
@@ -1941,16 +1949,16 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
         if (unshare_flags & CLONE_NEWUSER)
                 unshare_flags |= CLONE_THREAD | CLONE_FS;
         /*
-         * If unsharing a thread from a thread group, must also unshare vm.
-         */
-        if (unshare_flags & CLONE_THREAD)
-                unshare_flags |= CLONE_VM;
-        /*
          * If unsharing vm, must also unshare signal handlers.
          */
         if (unshare_flags & CLONE_VM)
                 unshare_flags |= CLONE_SIGHAND;
         /*
+         * If unsharing a signal handlers, must also unshare the signal queues.
+         */
+        if (unshare_flags & CLONE_SIGHAND)
+                unshare_flags |= CLONE_THREAD;
+        /*
          * If unsharing namespace, must also unshare filesystem information.
          */
         if (unshare_flags & CLONE_NEWNS)