[RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a shared sighand_struct

[Eric W. Biederman]

Old threading libraries used CLONE_SIGHAND without clone thread.
Modern threadding libraries always use CLONE_SIGHAND | CLONE_THREAD.

Therefore let's simplify our lives and stop supporting a case no one cares 
about.

Signed-off-by: "Eric W. Biederman" <ebied...@xmission.com>
---
 kernel/fork.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index fe6f1bf32bb9..0632ac1180be 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1515,6 +1515,13 @@ static __latent_entropy struct task_struct *copy_process(
        if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
                return ERR_PTR(-EINVAL);
 
+       /* Disallow CLONE_THREAD with a shared SIGHAND structure.  No
+        * one cares and supporting it leads to unnecessarily complex
+        * code.
+        */
+       if ((clone_flags & CLONE_THREAD) && 
(atomic_read(&current->sighand->count) > 1))
+               return ERR_PTR(-EINVAL);
+
        /*
         * Shared signal handlers imply shared VM. By way of the above,
         * thread groups also imply shared VM. Blocking this case allows
-- 
2.10.1