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Tue, 29 Sep 2026 06:46:39 -0700 (PDT) Received: from server.roeck-us.net ([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-885e28d7d23sm944357b3a.56.2026.09.29.06.46.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Sep 2026 06:46:39 -0700 (PDT) Sender: Guenter Roeck From: Guenter Roeck To: linux-watchdog@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Guenter Roeck Subject: [PATCH 1/8] watchdog: core: Clear wd_data pointer on errors Date: Tue, 29 Sep 2026 06:46:28 -0700 Message-ID: <20260929134635.2567137-2-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 In watchdog_cdev_register(), if device registration fails after the core watchdog_core_data structure is allocated and assigned to the persistent watchdog_device structure, the function frees the data but leaves a dangling pointer. During device registration, watchdog_cdev_register() links the newly allocated wd_data to wdd->wd_data. If a subsequent initialization step fails, such as the watchdog_kworker validation, dev_set_name(), misc_register(), or cdev_device_add(), the function cleans up by freeing wd_data via kfree() or put_device(). However, it fails to clear the wdd->wd_data pointer before returning. Furthermore, if cdev_device_add() fails after misc_register() exposed /dev/watchdog to userspace, a concurrent open may hold a reference to wd_data while the caller frees wdd, leaving wd_data->wdd dangling. Fix the problem by clearing wdd->wd_data on all error paths during watchdog registration, and clearing wd_data->wdd under wd_data->lock if cdev_device_add() fails. Fixes: b4ffb1909843 ("watchdog: Separate and maintain variables based on variable lifetime") Assisted-by: LLM Signed-off-by: Guenter Roeck --- drivers/watchdog/watchdog_dev.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c index e8c1fcb53c56..ed5b35184271 100644 --- a/drivers/watchdog/watchdog_dev.c +++ b/drivers/watchdog/watchdog_dev.c @@ -1033,6 +1033,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd) wdd->wd_data = wd_data; if (IS_ERR_OR_NULL(watchdog_kworker)) { + wdd->wd_data = NULL; kfree(wd_data); return -ENODEV; } @@ -1046,6 +1047,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd) dev_set_drvdata(&wd_data->dev, wdd); err = dev_set_name(&wd_data->dev, "watchdog%d", wdd->id); if (err) { + wdd->wd_data = NULL; put_device(&wd_data->dev); return err; } @@ -1066,6 +1068,7 @@ static int watchdog_cdev_register(struct watchdog_device *wdd) pr_err("%s: a legacy watchdog module is probably present.\n", wdd->info->identity); old_wd_data = NULL; + wdd->wd_data = NULL; put_device(&wd_data->dev); return err; } @@ -1084,6 +1087,10 @@ static int watchdog_cdev_register(struct watchdog_device *wdd) misc_deregister(&watchdog_miscdev); old_wd_data = NULL; } + mutex_lock(&wd_data->lock); + wd_data->wdd = NULL; + wdd->wd_data = NULL; + mutex_unlock(&wd_data->lock); put_device(&wd_data->dev); return err; } -- 2.45.2