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Thu, 8 Mar 2018 02:06:47 -0500 Received: from mail-bn3nam01on0130.outbound.protection.outlook.com ([104.47.33.130]:45246 "EHLO NAM01-BN3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755250AbeCHE4d (ORCPT ); Wed, 7 Mar 2018 23:56:33 -0500 From: Sasha Levin To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" CC: Guenter Roeck , Wim Van Sebroeck , Sasha Levin Subject: [PATCH AUTOSEL for 4.15 28/78] watchdog: Fix potential kref imbalance when opening watchdog Thread-Topic: [PATCH AUTOSEL for 4.15 28/78] watchdog: Fix potential kref imbalance when opening watchdog Thread-Index: AQHTtpnIz0Q9bdyCB0uIZmAFLFLXkQ== Date: Thu, 8 Mar 2018 04:56:13 +0000 Message-ID: <20180308045525.7662-28-alexander.levin@microsoft.com> References: <20180308045525.7662-1-alexander.levin@microsoft.com> In-Reply-To: <20180308045525.7662-1-alexander.levin@microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [52.168.54.252] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;DM5PR2101MB1111;7:GydmBaS2LVRYBY4SnFwRggod/Dt3zaWQigv+5IMtQ5ldBBrq8E3fRHhXstUQjIgnI2KKU+xAypscoLBIieLi87Hrga503Yb686s0M5MnE9s23xSs0UyokO7n22eMns2XQPlq3gonEoGn6G5WUNG2cR5crymRJ672ajHZ40R5akynsAkTXZr4cC2i+YxmCvTjQvTcQPwGEqaUDLs7zsmaMNCv24P5+rQGlV96A2H+HKUuVSsa/bjO9373G4nk9R2o;20:JiBtU/ZVuUQRkQldV5aoO6/Od5J3C8ea76nxKdvKlXaD6WkP8cHRbKBmGemDjojXePr0BA08XE1R3/TMjSB0tch7zOtyavDtxZPY3deOFS6LbVAVwYw401bnfzFVBOMnXFXwMqJQTEJZEd02ETp8KhiyYXDwBdrYhHM+SP8pGtk= x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 5ea34e08-981a-4921-4262-08d584b0f518 x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(3008032)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603328)(7193020);SRVR:DM5PR2101MB1111; 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x-microsoft-antispam-message-info: CumIdDsBiPiaV/hGWLfcgfqAvxbx0jzi1p2lYDYqP1dwKsyEUgXuhGtbmR63Trggxa0c490cxlCHCVbqwPdXUaz2arfb3lxUoUs7AZcm18mpmIf570z4HB5tVFIDayS+uqDmCLxigD832L9Oh6kEkMOOdyeq2BX+9bCg6mlMujyEG4l8sJ55iBj8f/sNW4p8AK8F/vgs+CRFNXS/IsHHzriGuGEmX8oxeJmn4aQCJKtVkSbPlUx1s0OEizK626XZM9ZZqFVQCbPQFCO6J44u2HwO+pXlEPHRupR2kMgZFjXZdRhbSboqnWqCYOhvOsWNX560ZT6VbGx1XuNGvVuscw== spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: 5ea34e08-981a-4921-4262-08d584b0f518 X-MS-Exchange-CrossTenant-originalarrivaltime: 08 Mar 2018 04:56:13.5603 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB1111 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Guenter Roeck [ Upstream commit 4bcd615fad6adddc68b058d498b30a9e0e0db77a ] If a watchdog driver's open function sets WDOG_HW_RUNNING with the expectation that the watchdog can not be stopped, but then stops the watchdog anyway in its stop function, kref_get() wil not be called in watchdog_open(). If the watchdog then stops on close, WDOG_HW_RUNNING will be cleared and kref_put() will be called, causing a kref imbalance. As result the character device data structure will be released, which in turn will cause the system to crash on the next call to watchdog_open(). Fixes: ee142889e32f5 ("watchdog: Introduce WDOG_HW_RUNNING flag") Signed-off-by: Guenter Roeck Signed-off-by: Wim Van Sebroeck Signed-off-by: Sasha Levin --- drivers/watchdog/watchdog_dev.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_de= v.c index 1e971a50d7fb..12fe47d8237b 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -769,6 +769,7 @@ static int watchdog_open(struct inode *inode, struct fi= le *file) { struct watchdog_core_data *wd_data; struct watchdog_device *wdd; + bool hw_running; int err; =20 /* Get the corresponding watchdog device */ @@ -788,7 +789,8 @@ static int watchdog_open(struct inode *inode, struct fi= le *file) * If the /dev/watchdog device is open, we don't want the module * to be unloaded. */ - if (!watchdog_hw_running(wdd) && !try_module_get(wdd->ops->owner)) { + hw_running =3D watchdog_hw_running(wdd); + if (!hw_running && !try_module_get(wdd->ops->owner)) { err =3D -EBUSY; goto out_clear; } @@ -799,7 +801,7 @@ static int watchdog_open(struct inode *inode, struct fi= le *file) =20 file->private_data =3D wd_data; =20 - if (!watchdog_hw_running(wdd)) + if (!hw_running) kref_get(&wd_data->kref); =20 /* dev/watchdog is a virtual (and thus non-seekable) filesystem */ --=20 2.14.1