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[72.110.77.234]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3472692e5d3sm14181601a91.9.2025.11.24.08.55.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Nov 2025 08:55:25 -0800 (PST) From: Gui-Dong Han To: steve.glendinning@shawell.net, linux@roeck-us.net Cc: linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, Gui-Dong Han Subject: [PATCH] hwmon: (emc2103) Add locking to avoid TOCTOU Date: Tue, 25 Nov 2025 00:55:08 +0800 Message-ID: <20251124165508.4667-1-hanguidong02@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The functions fan1_input_show and fan1_target_show check shared data for zero before using 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. Link: https://lore.kernel.org/all/CALbr=3DLYJ_ehtp53HXEVkSpYoub+XYSTU8Rg=3D= o1xxMJ8=3D5z8B-g@mail.gmail.com/ 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/emc2103.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/hwmon/emc2103.c b/drivers/hwmon/emc2103.c index 60eddc7b0270..9b8e925af030 100644 --- a/drivers/hwmon/emc2103.c +++ b/drivers/hwmon/emc2103.c @@ -277,8 +277,10 @@ fan1_input_show(struct device *dev, struct device_attr= ibute *da, char *buf) { struct emc2103_data *data =3D emc2103_update_device(dev); int rpm =3D 0; + mutex_lock(&data->update_lock); if (data->fan_tach !=3D 0) rpm =3D (FAN_RPM_FACTOR * data->fan_multiplier) / data->fan_tach; + mutex_unlock(&data->update_lock); return sprintf(buf, "%d\n", rpm); } =20 @@ -363,10 +365,12 @@ fan1_target_show(struct device *dev, struct device_at= tribute *da, char *buf) struct emc2103_data *data =3D emc2103_update_device(dev); int rpm =3D 0; =20 + mutex_lock(&data->update_lock); /* high byte of 0xff indicates disabled so return 0 */ if ((data->fan_target !=3D 0) && ((data->fan_target & 0x1fe0) !=3D 0x1fe0= )) rpm =3D (FAN_RPM_FACTOR * data->fan_multiplier) / data->fan_target; + mutex_unlock(&data->update_lock); =20 return sprintf(buf, "%d\n", rpm); } --=20 2.34.1