hwmon: (pmbus/max20730) Remove strlcpy occurences

strlcpy() reads the entire source buffer first.
This read may exceed the destination size limit.
This is both inefficient and can lead to linear read
overflows if a source string is not NUL-terminated [1].
In an effort to remove strlcpy() completely [2], replace
strlcpy() here with direct assignment.

strlcpy in this file is used to copy fixed-length strings which can be
completely avoided by direct assignment and is safe to do so. strlen()
is used to return the length of @tbuf.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89Signed-off-by: Azeem Shaikh <azeemshaikh38@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230712214307.2424810-1-azeemshaikh38@gmail.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/max20730.c

@@ -114,6 +114,7 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 	const struct pmbus_driver_info *info;
 	const struct max20730_data *data;
 	char tbuf[DEBUG_FS_DATA_MAX] = { 0 };
+	char *result = tbuf;
 	u16 val;
 
 	info = pmbus_get_driver_info(psu->client);
@@ -148,13 +149,13 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 			>> MAX20730_MFR_DEVSET1_TSTAT_BIT_POS;
 
 		if (val == 0)
-			len = strlcpy(tbuf, "2000\n", DEBUG_FS_DATA_MAX);
+			result = "2000\n";
 		else if (val == 1)
-			len = strlcpy(tbuf, "125\n", DEBUG_FS_DATA_MAX);
+			result = "125\n";
 		else if (val == 2)
-			len = strlcpy(tbuf, "62.5\n", DEBUG_FS_DATA_MAX);
+			result = "62.5\n";
 		else
-			len = strlcpy(tbuf, "32\n", DEBUG_FS_DATA_MAX);
+			result = "32\n";
 		break;
 	case MAX20730_DEBUGFS_INTERNAL_GAIN:
 		val = (data->mfr_devset1 & MAX20730_MFR_DEVSET1_RGAIN_MASK)
@@ -163,35 +164,35 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 		if (data->id == max20734) {
 			/* AN6209 */
 			if (val == 0)
-				len = strlcpy(tbuf, "0.8\n", DEBUG_FS_DATA_MAX);
+				result = "0.8\n";
 			else if (val == 1)
-				len = strlcpy(tbuf, "3.2\n", DEBUG_FS_DATA_MAX);
+				result = "3.2\n";
 			else if (val == 2)
-				len = strlcpy(tbuf, "1.6\n", DEBUG_FS_DATA_MAX);
+				result = "1.6\n";
 			else
-				len = strlcpy(tbuf, "6.4\n", DEBUG_FS_DATA_MAX);
+				result = "6.4\n";
 		} else if (data->id == max20730 || data->id == max20710) {
 			/* AN6042 or AN6140 */
 			if (val == 0)
-				len = strlcpy(tbuf, "0.9\n", DEBUG_FS_DATA_MAX);
+				result = "0.9\n";
 			else if (val == 1)
-				len = strlcpy(tbuf, "3.6\n", DEBUG_FS_DATA_MAX);
+				result = "3.6\n";
 			else if (val == 2)
-				len = strlcpy(tbuf, "1.8\n", DEBUG_FS_DATA_MAX);
+				result = "1.8\n";
 			else
-				len = strlcpy(tbuf, "7.2\n", DEBUG_FS_DATA_MAX);
+				result = "7.2\n";
 		} else if (data->id == max20743) {
 			/* AN6042 */
 			if (val == 0)
-				len = strlcpy(tbuf, "0.45\n", DEBUG_FS_DATA_MAX);
+				result = "0.45\n";
 			else if (val == 1)
-				len = strlcpy(tbuf, "1.8\n", DEBUG_FS_DATA_MAX);
+				result = "1.8\n";
 			else if (val == 2)
-				len = strlcpy(tbuf, "0.9\n", DEBUG_FS_DATA_MAX);
+				result = "0.9\n";
 			else
-				len = strlcpy(tbuf, "3.6\n", DEBUG_FS_DATA_MAX);
+				result = "3.6\n";
 		} else {
-			len = strlcpy(tbuf, "Not supported\n", DEBUG_FS_DATA_MAX);
+			result = "Not supported\n";
 		}
 		break;
 	case MAX20730_DEBUGFS_BOOT_VOLTAGE:
@@ -199,26 +200,26 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 			>> MAX20730_MFR_DEVSET1_VBOOT_BIT_POS;
 
 		if (val == 0)
-			len = strlcpy(tbuf, "0.6484\n", DEBUG_FS_DATA_MAX);
+			result = "0.6484\n";
 		else if (val == 1)
-			len = strlcpy(tbuf, "0.8984\n", DEBUG_FS_DATA_MAX);
+			result = "0.8984\n";
 		else if (val == 2)
-			len = strlcpy(tbuf, "1.0\n", DEBUG_FS_DATA_MAX);
+			result = "1.0\n";
 		else
-			len = strlcpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
+			result = "Invalid\n";
 		break;
 	case MAX20730_DEBUGFS_OUT_V_RAMP_RATE:
 		val = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_VRATE)
 			>> MAX20730_MFR_DEVSET2_VRATE_BIT_POS;
 
 		if (val == 0)
-			len = strlcpy(tbuf, "4\n", DEBUG_FS_DATA_MAX);
+			result = "4\n";
 		else if (val == 1)
-			len = strlcpy(tbuf, "2\n", DEBUG_FS_DATA_MAX);
+			result = "2\n";
 		else if (val == 2)
-			len = strlcpy(tbuf, "1\n", DEBUG_FS_DATA_MAX);
+			result = "1\n";
 		else
-			len = strlcpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
+			result = "Invalid\n";
 		break;
 	case MAX20730_DEBUGFS_OC_PROTECT_MODE:
 		ret = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_OCPM_MASK)
@@ -230,13 +231,13 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 			>> MAX20730_MFR_DEVSET2_SS_BIT_POS;
 
 		if (val == 0)
-			len = strlcpy(tbuf, "0.75\n", DEBUG_FS_DATA_MAX);
+			result = "0.75\n";
 		else if (val == 1)
-			len = strlcpy(tbuf, "1.5\n", DEBUG_FS_DATA_MAX);
+			result = "1.5\n";
 		else if (val == 2)
-			len = strlcpy(tbuf, "3\n", DEBUG_FS_DATA_MAX);
+			result = "3\n";
 		else
-			len = strlcpy(tbuf, "6\n", DEBUG_FS_DATA_MAX);
+			result = "6\n";
 		break;
 	case MAX20730_DEBUGFS_IMAX:
 		ret = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_IMAX_MASK)
@@ -287,10 +288,11 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
 				"%d.%d\n", ret / 10000, ret % 10000);
 		break;
 	default:
-		len = strlcpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
+		result = "Invalid\n";
 	}
 
-	return simple_read_from_buffer(buf, count, ppos, tbuf, len);
+	len = strlen(result);
+	return simple_read_from_buffer(buf, count, ppos, result, len);
 }
 
 static const struct file_operations max20730_fops = {