Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Bernd Edlinger <bernd.edlinger@hotmail.de>
Cc:     Christian Brauner <christian.brauner@ubuntu.com>,
        Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, Jonathan Corbet <corbet@lwn.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Andrei Vagin <avagin@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        "Peter Zijlstra \(Intel\)" <peterz@infradead.org>,
        Yuyang Du <duyuyang@gmail.com>,
        David Hildenbrand <david@redhat.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        David Howells <dhowells@redhat.com>,
        James Morris <jamorris@linux.microsoft.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Shakeel Butt <shakeelb@google.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Christian Kellner <christian@kellner.me>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Aleksa Sarai <cyphar@cyphar.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>,
        "linux-doc\@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-fsdevel\@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-mm\@kvack.org" <linux-mm@kvack.org>,
        "stable\@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-api\@vger.kernel.org" <linux-api@vger.kernel.org>
References: <AM6PR03MB5170EB4427BF5C67EE98FF09E4E60@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <87k142lpfz.fsf@x220.int.ebiederm.org>
        <AM6PR03MB51704206634C009500A8080DE4E70@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <875zfmloir.fsf@x220.int.ebiederm.org>
        <AM6PR03MB51707ABF20B6CBBECC34865FE4E70@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <87v9nmjulm.fsf@x220.int.ebiederm.org>
        <AM6PR03MB5170B976E6387FDDAD59A118E4E70@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <202003021531.C77EF10@keescook>
        <20200303085802.eqn6jbhwxtmz4j2x@wittgenstein>
        <AM6PR03MB5170285B336790D3450E2644E4E40@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <87v9nlii0b.fsf@x220.int.ebiederm.org>
        <AM6PR03MB5170609D44967E044FD1BE40E4E40@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <87a74xi4kz.fsf@x220.int.ebiederm.org>
        <AM6PR03MB51705AA3009B4986BB6EF92FE4E50@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <87r1y8dqqz.fsf@x220.int.ebiederm.org>
        <AM6PR03MB517053AED7DC89F7C0704B7DE4E50@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <AM6PR03MB51703B44170EAB4626C9B2CAE4E20@AM6PR03MB5170.eurprd03.prod.outlook.com>
        <87tv32cxmf.fsf_-_@x220.int.ebiederm.org>
        <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org>
Date:   Sun, 08 Mar 2020 16:36:17 -0500
In-Reply-To: <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org> (Eric W. Biederman's
        message of "Sun, 08 Mar 2020 16:34:37 -0500")
Message-ID: <87k13u5y26.fsf_-_@x220.int.ebiederm.org>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Subject: [PATCH v2 2/5] exec: Factor unshare_sighand out of de_thread and call it separately
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


This makes the code clearer and makes it easier to implement a mutex
that is not taken over any locations that may block indefinitely waiting
for userspace.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 fs/exec.c | 39 ++++++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index c3f34791f2f0..ff74b9a74d34 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1194,6 +1194,23 @@ static int de_thread(struct task_struct *tsk)
 	flush_itimer_signals();
 #endif
 
+	BUG_ON(!thread_group_leader(tsk));
+	return 0;
+
+killed:
+	/* protects against exit_notify() and __exit_signal() */
+	read_lock(&tasklist_lock);
+	sig->group_exit_task = NULL;
+	sig->notify_count = 0;
+	read_unlock(&tasklist_lock);
+	return -EAGAIN;
+}
+
+
+static int unshare_sighand(struct task_struct *me)
+{
+	struct sighand_struct *oldsighand = me->sighand;
+
 	if (refcount_read(&oldsighand->count) != 1) {
 		struct sighand_struct *newsighand;
 		/*
@@ -1210,23 +1227,13 @@ static int de_thread(struct task_struct *tsk)
 
 		write_lock_irq(&tasklist_lock);
 		spin_lock(&oldsighand->siglock);
-		rcu_assign_pointer(tsk->sighand, newsighand);
+		rcu_assign_pointer(me->sighand, newsighand);
 		spin_unlock(&oldsighand->siglock);
 		write_unlock_irq(&tasklist_lock);
 
 		__cleanup_sighand(oldsighand);
 	}
-
-	BUG_ON(!thread_group_leader(tsk));
 	return 0;
-
-killed:
-	/* protects against exit_notify() and __exit_signal() */
-	read_lock(&tasklist_lock);
-	sig->group_exit_task = NULL;
-	sig->notify_count = 0;
-	read_unlock(&tasklist_lock);
-	return -EAGAIN;
 }
 
 char *__get_task_comm(char *buf, size_t buf_size, struct task_struct *tsk)
@@ -1264,13 +1271,19 @@ int flush_old_exec(struct linux_binprm * bprm)
 	int retval;
 
 	/*
-	 * Make sure we have a private signal table and that
-	 * we are unassociated from the previous thread group.
+	 * Make this the only thread in the thread group.
 	 */
 	retval = de_thread(me);
 	if (retval)
 		goto out;
 
+	/*
+	 * Make the signal table private.
+	 */
+	retval = unshare_sighand(me);
+	if (retval)
+		goto out;
+
 	/*
 	 * Must be called _before_ exec_mmap() as bprm->mm is
 	 * not visibile until then. This also enables the update
-- 
2.25.0