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Tue, 29 Sep 2026 06:46:41 -0700 (PDT) Received: from server.roeck-us.net ([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cc7cf5a2f74sm474872a12.10.2026.09.29.06.46.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Sep 2026 06:46:40 -0700 (PDT) Sender: Guenter Roeck From: Guenter Roeck To: linux-watchdog@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Guenter Roeck Subject: [PATCH 2/8] watchdog: core: Add missing locks Date: Tue, 29 Sep 2026 06:46:29 -0700 Message-ID: <20260929134635.2567137-3-linux@roeck-us.net> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20260929134635.2567137-1-linux@roeck-us.net> References: <20260929134635.2567137-1-linux@roeck-us.net> Precedence: bulk X-Mailing-List: linux-watchdog@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add missing locks to watchdog_open(), watchdog_cdev_unregister(), and watchdog_set_last_hw_keepalive(). Also protect old_wd_data with its own lock to prevent its modification while in use, acquiring wd_data->lock before releasing old_wd_data_lock in watchdog_open() to avoid a TOCTOU race, and keeping misc_deregister() outside old_wd_data_lock to avoid lock ordering inversion with misc_mtx. Fixes: b4ffb1909843 ("watchdog: Separate and maintain variables based on variable lifetime") Assisted-by: LLM Signed-off-by: Guenter Roeck --- drivers/watchdog/watchdog_dev.c | 42 ++++++++++++++++++++++++++++----- 1 file changed, 36 insertions(+), 6 deletions(-) diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c index ed5b35184271..50224877ff49 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -55,6 +55,7 @@ static dev_t watchdog_devt; /* Reference to watchdog device behind /dev/watchdog */ static struct watchdog_core_data *old_wd_data; +static DEFINE_MUTEX(old_wd_data_lock); static struct kthread_worker *watchdog_kworker; @@ -869,17 +870,32 @@ static int watchdog_open(struct inode *inode, struct file *file) int err; /* Get the corresponding watchdog device */ - if (imajor(inode) == MISC_MAJOR) + if (imajor(inode) == MISC_MAJOR) { + mutex_lock(&old_wd_data_lock); wd_data = old_wd_data; - else + if (!wd_data) { + mutex_unlock(&old_wd_data_lock); + return -ENODEV; + } + mutex_lock(&wd_data->lock); + mutex_unlock(&old_wd_data_lock); + } else { wd_data = container_of(inode->i_cdev, struct watchdog_core_data, cdev); + mutex_lock(&wd_data->lock); + } /* the watchdog is single open! */ - if (test_and_set_bit(_WDOG_DEV_OPEN, &wd_data->status)) + if (test_and_set_bit(_WDOG_DEV_OPEN, &wd_data->status)) { + mutex_unlock(&wd_data->lock); return -EBUSY; + } wdd = wd_data->wdd; + if (!wdd) { + err = -ENODEV; + goto out_clear; + } /* * If the /dev/watchdog device is open, we don't want the module @@ -909,6 +925,8 @@ static int watchdog_open(struct inode *inode, struct file *file) */ wd_data->open_deadline = KTIME_MAX; + mutex_unlock(&wd_data->lock); + /* dev/watchdog is a virtual (and thus non-seekable) filesystem */ return stream_open(inode, file); @@ -916,6 +934,7 @@ static int watchdog_open(struct inode *inode, struct file *file) module_put(wd_data->wdd->ops->owner); out_clear: clear_bit(_WDOG_DEV_OPEN, &wd_data->status); + mutex_unlock(&wd_data->lock); return err; } @@ -1085,7 +1104,9 @@ static int watchdog_cdev_register(struct watchdog_device *wdd) wdd->id, MAJOR(watchdog_devt), wdd->id); if (wdd->id == 0) { misc_deregister(&watchdog_miscdev); + mutex_lock(&old_wd_data_lock); old_wd_data = NULL; + mutex_unlock(&old_wd_data_lock); } mutex_lock(&wd_data->lock); wd_data->wdd = NULL; @@ -1131,9 +1152,12 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd) cdev_device_del(&wd_data->cdev, &wd_data->dev); if (wdd->id == 0) { misc_deregister(&watchdog_miscdev); + mutex_lock(&old_wd_data_lock); old_wd_data = NULL; + mutex_unlock(&old_wd_data_lock); } + mutex_lock(&wd_data->lock); if (watchdog_active(wdd) && test_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status)) { watchdog_stop(wdd); @@ -1141,7 +1165,6 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd) watchdog_hrtimer_pretimeout_stop(wdd); - mutex_lock(&wd_data->lock); wd_data->wdd = NULL; wdd->wd_data = NULL; mutex_unlock(&wd_data->lock); @@ -1208,20 +1231,27 @@ int watchdog_set_last_hw_keepalive(struct watchdog_device *wdd, { struct watchdog_core_data *wd_data; ktime_t now; + int ret = 0; if (!wdd) return -EINVAL; wd_data = wdd->wd_data; + if (!wd_data) + return -ENODEV; + + mutex_lock(&wd_data->lock); now = ktime_get(); wd_data->last_hw_keepalive = ktime_sub(now, ms_to_ktime(last_ping_ms)); if (watchdog_hw_running(wdd) && handle_boot_enabled) - return __watchdog_ping(wdd); + ret = __watchdog_ping(wdd); - return 0; + mutex_unlock(&wd_data->lock); + + return ret; } EXPORT_SYMBOL_GPL(watchdog_set_last_hw_keepalive); -- 2.45.2