linux-kernel - [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a shared sighand

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Message-ID: <87k2728lrp.fsf_-_@xmission.com>
Date:   Sun, 02 Apr 2017 17:52:58 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Aleksa Sarai <asarai@...e.com>,
        Andy Lutomirski <luto@...capital.net>,
        Attila Fazekas <afazekas@...hat.com>,
        Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        Ulrich Obergfell <uobergfe@...hat.com>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
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@...ssion.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