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[75.221.66.7]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-11dcb057cb0sm20974322c88.9.2025.11.28.04.43.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Nov 2025 04:44:01 -0800 (PST) From: Gui-Dong Han To: linux@roeck-us.net Cc: linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, Gui-Dong Han , stable@vger.kernel.org Subject: [PATCH] hwmon: (max6620) Add locking to avoid TOCTOU Date: Fri, 28 Nov 2025 20:43:51 +0800 Message-ID: <20251128124351.3778-1-hanguidong02@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-hwmon@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The function max6620_read checks shared data (tach and target) for zero before passing it to max6620_fan_tach_to_rpm, which uses it as a divisor. These accesses are currently lockless. If the data changes to zero between the check and the division, it causes a divide-by-zero error. Explicitly acquire the update lock around these checks and calculations to ensure the data remains stable, preventing Time-of-Check to Time-of-Use (TOCTOU) race conditions. This change also aligns the locking behavior with the hwmon_fan_alarm case, which already uses the update lock. Link: https://lore.kernel.org/all/CALbr=LYJ_ehtp53HXEVkSpYoub+XYSTU8Rg=o1xxMJ8=5z8B-g@mail.gmail.com/ Fixes: e8ac01e5db32 ("hwmon: Add Maxim MAX6620 hardware monitoring driver") Cc: stable@vger.kernel.org Signed-off-by: Gui-Dong Han --- Based on the discussion in the link, I will submit a series of patches to address TOCTOU issues in the hwmon subsystem by converting macros to functions or adjusting locking where appropriate. --- drivers/hwmon/max6620.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/hwmon/max6620.c b/drivers/hwmon/max6620.c index 13201fb755c9..0dce2f5cb61b 100644 --- a/drivers/hwmon/max6620.c +++ b/drivers/hwmon/max6620.c @@ -290,20 +290,24 @@ max6620_read(struct device *dev, enum hwmon_sensor_types type, u32 attr, *val = max6620_fan_div_from_reg(data->fandyn[channel]); break; case hwmon_fan_input: + mutex_lock(&data->update_lock); if (data->tach[channel] == 0) { *val = 0; } else { div = max6620_fan_div_from_reg(data->fandyn[channel]); *val = max6620_fan_tach_to_rpm(div, data->tach[channel]); } + mutex_unlock(&data->update_lock); break; case hwmon_fan_target: + mutex_lock(&data->update_lock); if (data->target[channel] == 0) { *val = 0; } else { div = max6620_fan_div_from_reg(data->fandyn[channel]); *val = max6620_fan_tach_to_rpm(div, data->target[channel]); } + mutex_unlock(&data->update_lock); break; default: return -EOPNOTSUPP; -- 2.43.0