hwmon: (pmbus/isl68137) Add mutex protection for AVS enable sysfs attributes

The custom avs0_enable and avs1_enable sysfs attributes access PMBus
registers through the exported API helpers (pmbus_read_byte_data,
pmbus_read_word_data, pmbus_write_word_data, pmbus_update_byte_data)
without holding the PMBus update_lock mutex. These exported helpers do
not acquire the mutex internally, unlike the core's internal callers
which hold the lock before invoking them.

The store callback is especially vulnerable: it performs a multi-step
read-modify-write sequence (read VOUT_COMMAND, write VOUT_COMMAND, then
update OPERATION) where concurrent access from another thread could
interleave and corrupt the register state.

Add pmbus_lock_interruptible()/pmbus_unlock() around both the show and
store callbacks to serialize PMBus register access with the rest of the
driver.

Fixes: 038a9c3d1e424 ("hwmon: (pmbus/isl68137) Add driver for Intersil ISL68137 PWM Controller")
Cc: stable@vger.kernel.org
Signed-off-by: Sanman Pradhan <psanman@juniper.net>
Link: https://lore.kernel.org/r/20260319173055.125271-3-sanman.pradhan@hpe.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/pmbus/isl68137.c b/drivers/hwmon/pmbus/isl68137.c
index e7dac26b5be615213a5844b425e95941f829133d..3e3a887aad050f618a88696382f1c17c7e1980a1 100644 (file)
--- a/drivers/hwmon/pmbus/isl68137.c
+++ b/drivers/hwmon/pmbus/isl68137.c
@@ -96,7 +96,15 @@ static ssize_t isl68137_avs_enable_show_page(struct i2c_client *client,
                                             int page,
                                             char *buf)
 {
-       int val = pmbus_read_byte_data(client, page, PMBUS_OPERATION);
+       int val;
+
+       val = pmbus_lock_interruptible(client);
+       if (val)
+               return val;
+
+       val = pmbus_read_byte_data(client, page, PMBUS_OPERATION);
+
+       pmbus_unlock(client);
 
        if (val < 0)
                return val;
@@ -118,6 +126,10 @@ static ssize_t isl68137_avs_enable_store_page(struct i2c_client *client,
 
        op_val = result ? ISL68137_VOUT_AVS : 0;
 
+       rc = pmbus_lock_interruptible(client);
+       if (rc)
+               return rc;
+
        /*
         * Writes to VOUT setpoint over AVSBus will persist after the VRM is
         * switched to PMBus control. Switching back to AVSBus control
@@ -129,17 +141,20 @@ static ssize_t isl68137_avs_enable_store_page(struct i2c_client *client,
                rc = pmbus_read_word_data(client, page, 0xff,
                                          PMBUS_VOUT_COMMAND);
                if (rc < 0)
-                       return rc;
+                       goto unlock;
 
                rc = pmbus_write_word_data(client, page, PMBUS_VOUT_COMMAND,
                                           rc);
                if (rc < 0)
-                       return rc;
+                       goto unlock;
        }
 
        rc = pmbus_update_byte_data(client, page, PMBUS_OPERATION,
                                    ISL68137_VOUT_AVS, op_val);
 
+unlock:
+       pmbus_unlock(client);
+
        return (rc < 0) ? rc : count;
 }