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

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" <ebiederm@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
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