[PATCH] thermal: sysfs: Use sysfs_emit_at() in trans_table_show()

[Thorsten Blum <thorsten.blum@linux.dev>]

Replace snprintf() with sysfs_emit_at() in trans_table_show().
sysfs_emit_at() is preferred for formatting sysfs output because it
provides safer bounds checking.

Convert multiple PAGE_SIZE length checks to check the number of bytes
actually copied by sysfs_emit_at(), thus avoiding manual buffer size
accounting.

Consistently return -EFBIG when the transition table output exceeds the
sysfs buffer, including the header row.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 drivers/thermal/thermal_sysfs.c | 49 ++++++++++++++++-----------------
 1 file changed, 24 insertions(+), 25 deletions(-)

diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index b44abfc997ed..adbcb2c011e8 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -706,7 +706,7 @@ static ssize_t trans_table_show(struct device *dev,
 	struct thermal_cooling_device *cdev = to_cooling_device(dev);
 	struct cooling_dev_stats *stats;
 	ssize_t len = 0;
-	int i, j;
+	int i, j, copied;
 
 	guard(cooling_dev)(cdev);
 
@@ -714,41 +714,40 @@ static ssize_t trans_table_show(struct device *dev,
 	if (!stats)
 		return -ENODATA;
 
-	len += snprintf(buf + len, PAGE_SIZE - len, " From  :    To\n");
-	len += snprintf(buf + len, PAGE_SIZE - len, "       : ");
+	len += sysfs_emit_at(buf, len, " From  :    To\n");
+	len += sysfs_emit_at(buf, len, "       : ");
 	for (i = 0; i <= cdev->max_state; i++) {
-		if (len >= PAGE_SIZE)
-			break;
-		len += snprintf(buf + len, PAGE_SIZE - len, "state%2u  ", i);
+		copied = sysfs_emit_at(buf, len, "state%2u  ", i);
+		if (!copied)
+			goto buf_full;
+		len += copied;
 	}
-	if (len >= PAGE_SIZE)
-		return PAGE_SIZE;
-
-	len += snprintf(buf + len, PAGE_SIZE - len, "\n");
+	len += sysfs_emit_at(buf, len, "\n");
 
 	for (i = 0; i <= cdev->max_state; i++) {
-		if (len >= PAGE_SIZE)
-			break;
-
-		len += snprintf(buf + len, PAGE_SIZE - len, "state%2u:", i);
+		copied = sysfs_emit_at(buf, len, "state%2u:", i);
+		if (!copied)
+			goto buf_full;
+		len += copied;
 
 		for (j = 0; j <= cdev->max_state; j++) {
-			if (len >= PAGE_SIZE)
-				break;
-			len += snprintf(buf + len, PAGE_SIZE - len, "%8u ",
+			copied = sysfs_emit_at(buf, len, "%8u ",
 				stats->trans_table[i * (cdev->max_state + 1) + j]);
+			if (!copied)
+				goto buf_full;
+			len += copied;
 		}
-		if (len >= PAGE_SIZE)
-			break;
-		len += snprintf(buf + len, PAGE_SIZE - len, "\n");
-	}
-
-	if (len >= PAGE_SIZE) {
-		pr_warn_once("Thermal transition table exceeds PAGE_SIZE. Disabling\n");
-		len = -EFBIG;
+		copied = sysfs_emit_at(buf, len, "\n");
+		if (!copied)
+			goto buf_full;
+		len += copied;
 	}
 
 	return len;
+
+buf_full:
+	pr_warn_once("Thermal transition table exceeds PAGE_SIZE. Disabling\n");
+	return -EFBIG;
 }
 
 static DEVICE_ATTR_RO(total_trans);