[PATCH v4 3/3] hwmon: (pmbus/adm1266) serialize sequencer_state debugfs read with pmbus_lock

[Abdurrahman Hussain]

adm1266_state_read() backs the sequencer_state debugfs entry and
issues an i2c_smbus_read_word_data(client, ADM1266_READ_STATE)
against the device without taking pmbus_lock.  The pmbus_core
framework holds pmbus_lock around its own multi-transaction
sequences (notably the "set PAGE, then read paged register" pattern
used by hwmon attributes), so an unlocked debugfs reader can land
between a PAGE write and the subsequent paged read in another
thread.  READ_STATE itself is not paged, so it cannot corrupt the
PAGE register in flight, but the same defensive serialisation that
applies to the GPIO accessors applies here: any direct device
access from outside pmbus_core should be ordered with respect to
pmbus_core's own.

Take pmbus_lock at the top of adm1266_state_read() via the
scope-based guard().

Fixes: ed1ff457e187 ("hwmon: (pmbus/adm1266) add debugfs for states")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Abdurrahman Hussain <abdurrahman@xxxxxxxxxx>
---
 drivers/hwmon/pmbus/adm1266.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hwmon/pmbus/adm1266.c b/drivers/hwmon/pmbus/adm1266.c
index 2edf3a424679..1425371bf1be 100644
--- a/drivers/hwmon/pmbus/adm1266.c
+++ b/drivers/hwmon/pmbus/adm1266.c
@@ -323,6 +323,7 @@ static int adm1266_state_read(struct seq_file *s, void *pdata)
 	struct i2c_client *client = to_i2c_client(dev);
 	int ret;
 
+	guard(pmbus_lock)(client);
 	ret = i2c_smbus_read_word_data(client, ADM1266_READ_STATE);
 	if (ret < 0)
 		return ret;

-- 
2.53.0