thermal: sysfs: Use sysfs_emit_at() in trans_table_show()

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>
Link: https://patch.msgid.link/20260719132251.31936-3-thorsten.blum@linux.dev
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index b44abfc997edf3a98197b50c7aa84d190123a87d..adbcb2c011e83dfa0d4e66e983bb085db282467f 100644 (file)
--- 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);