From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S932397AbcFIVRy (ORCPT <rfc822;w@1wt.eu>);
	Thu, 9 Jun 2016 17:17:54 -0400
Received: from youngberry.canonical.com ([91.189.89.112]:50721 "EHLO
	youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S932328AbcFIVRt (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 9 Jun 2016 17:17:49 -0400
From: Kamal Mostafa <kamal@canonical.com>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        kernel-team@lists.ubuntu.com
Cc: Alan Cox <alan@linux.intel.com>, Jiri Slaby <jslaby@suse.cz>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kamal Mostafa <kamal@canonical.com>
Subject: [PATCH 4.2.y-ckt 035/206] TTY: n_gsm, fix false positive WARN_ON
Date: Thu,  9 Jun 2016 14:14:04 -0700
Message-Id: <1465507015-23052-36-git-send-email-kamal@canonical.com>
X-Mailer: git-send-email 2.7.4
In-Reply-To: <1465507015-23052-1-git-send-email-kamal@canonical.com>
References: <1465507015-23052-1-git-send-email-kamal@canonical.com>
X-Extended-Stable: 4.2
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

4.2.8-ckt12 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Jiri Slaby <jslaby@suse.cz>

commit d175feca89a1c162f60f4e3560ca7bc9437c65eb upstream.

Dmitry reported, that the current cleanup code in n_gsm can trigger a
warning:
WARNING: CPU: 2 PID: 24238 at drivers/tty/n_gsm.c:2048 gsm_cleanup_mux+0x166/0x6b0()
...
Call Trace:
...
 [<ffffffff81247ab9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:490
 [<ffffffff828d0456>] gsm_cleanup_mux+0x166/0x6b0 drivers/tty/n_gsm.c:2048
 [<ffffffff828d4d87>] gsmld_open+0x5b7/0x7a0 drivers/tty/n_gsm.c:2386
 [<ffffffff828b9078>] tty_ldisc_open.isra.2+0x78/0xd0 drivers/tty/tty_ldisc.c:447
 [<ffffffff828b973a>] tty_set_ldisc+0x1ca/0xa70 drivers/tty/tty_ldisc.c:567
 [<     inline     >] tiocsetd drivers/tty/tty_io.c:2650
 [<ffffffff828a14ea>] tty_ioctl+0xb2a/0x2140 drivers/tty/tty_io.c:2883
...

But this is a legal path when open fails to find a space in the
gsm_mux array and tries to clean up. So make it a standard test
instead of a warning.

Reported-by: "Dmitry Vyukov" <dvyukov@google.com>
Cc: Alan Cox <alan@linux.intel.com>
Link: http://lkml.kernel.org/r/CACT4Y+bHQbAB68VFi7Romcs-Z9ZW3kQRvcq+BvHH1oa5NcAdLA@mail.gmail.com
Fixes: 5a640967 ("tty/n_gsm.c: fix a memory leak in gsmld_open()")
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 drivers/tty/n_gsm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 382d3fc..25444a1 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2045,7 +2045,9 @@ static void gsm_cleanup_mux(struct gsm_mux *gsm)
 		}
 	}
 	spin_unlock(&gsm_mux_lock);
-	WARN_ON(i == MAX_MUX);
+	/* open failed before registering => nothing to do */
+	if (i == MAX_MUX)
+		return;
 
 	/* In theory disconnecting DLCI 0 is sufficient but for some
 	   modems this is apparently not the case. */
-- 
2.7.4