hwmon: (pmbus/max20730) use scnprintf() instead of snprintf()

The snprintf() function returns the number of characters which would
have been printed if there were enough space, but the scnprintf()
returns the number of characters which were actually printed.  If the
buffer is not large enough, then using snprintf() would result in a
read overflow and an information leak.

Fixes: 8910c0b ("hwmon: (pmbus/max20730) add device monitoring via debugfs")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20201022070824.GC2817762@mwanda
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/max20730.c

@@ -122,8 +122,8 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 	switch (idx) {
 	case MAX20730_DEBUGFS_VOUT_MIN:
 		ret = VOLT_FROM_REG(data->mfr_voutmin * 10000);
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX, "%d.%d\n",
-			       ret / 10000, ret % 10000);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX, "%d.%d\n",
+				ret / 10000, ret % 10000);
 		break;
 	case MAX20730_DEBUGFS_FREQUENCY:
 		val = (data->mfr_devset1 & MAX20730_MFR_DEVSET1_FSW_MASK)
@@ -141,7 +141,7 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 			ret = 800;
 		else
 			ret = 900;
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
 		break;
 	case MAX20730_DEBUGFS_PG_DELAY:
 		val = (data->mfr_devset1 & MAX20730_MFR_DEVSET1_TSTAT_MASK)
@@ -223,7 +223,7 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 	case MAX20730_DEBUGFS_OC_PROTECT_MODE:
 		ret = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_OCPM_MASK)
 			>> MAX20730_MFR_DEVSET2_OCPM_BIT_POS;
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
 		break;
 	case MAX20730_DEBUGFS_SS_TIMING:
 		val = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_SS_MASK)
@@ -241,50 +241,50 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 	case MAX20730_DEBUGFS_IMAX:
 		ret = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_IMAX_MASK)
 			>> MAX20730_MFR_DEVSET2_IMAX_BIT_POS;
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
 		break;
 	case MAX20730_DEBUGFS_OPERATION:
 		ret = i2c_smbus_read_byte_data(psu->client, PMBUS_OPERATION);
 		if (ret < 0)
 			return ret;
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
 		break;
 	case MAX20730_DEBUGFS_ON_OFF_CONFIG:
 		ret = i2c_smbus_read_byte_data(psu->client, PMBUS_ON_OFF_CONFIG);
 		if (ret < 0)
 			return ret;
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
 		break;
 	case MAX20730_DEBUGFS_SMBALERT_MASK:
 		ret = i2c_smbus_read_word_data(psu->client,
 					       PMBUS_SMB_ALERT_MASK);
 		if (ret < 0)
 			return ret;
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
 		break;
 	case MAX20730_DEBUGFS_VOUT_MODE:
 		ret = i2c_smbus_read_byte_data(psu->client, PMBUS_VOUT_MODE);
 		if (ret < 0)
 			return ret;
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX, "%d\n", ret);
 		break;
 	case MAX20730_DEBUGFS_VOUT_COMMAND:
 		ret = i2c_smbus_read_word_data(psu->client, PMBUS_VOUT_COMMAND);
 		if (ret < 0)
 			return ret;
 
 		ret = VOLT_FROM_REG(ret * 10000);
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX,
-			       "%d.%d\n", ret / 10000, ret % 10000);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX,
+				"%d.%d\n", ret / 10000, ret % 10000);
 		break;
 	case MAX20730_DEBUGFS_VOUT_MAX:
 		ret = i2c_smbus_read_word_data(psu->client, PMBUS_VOUT_MAX);
 		if (ret < 0)
 			return ret;
 
 		ret = VOLT_FROM_REG(ret * 10000);
-		len = snprintf(tbuf, DEBUG_FS_DATA_MAX,
-			       "%d.%d\n", ret / 10000, ret % 10000);
+		len = scnprintf(tbuf, DEBUG_FS_DATA_MAX,
+				"%d.%d\n", ret / 10000, ret % 10000);
 		break;
 	default:
 		len = strlcpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);