mac80211: fix incorrect strlen of .write in debugfs

This fixes strlen mismatch problems happening in some .write callbacks
of debugfs.

When trying to configure airtime_flags in debugfs, an error appeared:
ash: write error: Invalid argument

The error is returned from kstrtou16() since a wrong length makes it
miss the real end of input string.  To fix this, use count as the string
length, and set proper end of string for a char buffer.

The debug print is shown - airtime_flags_write: count = 2, len = 8,
where the actual length is 2, but "len = strlen(buf)" gets 8.

Also cleanup the other similar cases for the sake of consistency.
Signed-off-by: Sujuan Chen <sujuan.chen@mediatek.com>
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Link: https://lore.kernel.org/r/20210112032028.7482-1-shayne.chen@mediatek.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/debugfs.c

@@ -120,18 +120,17 @@ static ssize_t aqm_write(struct file *file,
 {
 	struct ieee80211_local *local = file->private_data;
 	char buf[100];
-	size_t len;
 
-	if (count > sizeof(buf))
+	if (count >= sizeof(buf))
 		return -EINVAL;
 
 	if (copy_from_user(buf, user_buf, count))
 		return -EFAULT;
 
-	buf[sizeof(buf) - 1] = '\0';
-	len = strlen(buf);
-	if (len > 0 && buf[len-1] == '\n')
-		buf[len-1] = 0;
+	if (count && buf[count - 1] == '\n')
+		buf[count - 1] = '\0';
+	else
+		buf[count] = '\0';
 
 	if (sscanf(buf, "fq_limit %u", &local->fq.limit) == 1)
 		return count;
@@ -177,18 +176,17 @@ static ssize_t airtime_flags_write(struct file *file,
 {
 	struct ieee80211_local *local = file->private_data;
 	char buf[16];
-	size_t len;
 
-	if (count > sizeof(buf))
+	if (count >= sizeof(buf))
 		return -EINVAL;
 
 	if (copy_from_user(buf, user_buf, count))
 		return -EFAULT;
 
-	buf[sizeof(buf) - 1] = 0;
-	len = strlen(buf);
-	if (len > 0 && buf[len - 1] == '\n')
-		buf[len - 1] = 0;
+	if (count && buf[count - 1] == '\n')
+		buf[count - 1] = '\0';
+	else
+		buf[count] = '\0';
 
 	if (kstrtou16(buf, 0, &local->airtime_flags))
 		return -EINVAL;
@@ -237,20 +235,19 @@ static ssize_t aql_txq_limit_write(struct file *file,
 {
 	struct ieee80211_local *local = file->private_data;
 	char buf[100];
-	size_t len;
 	u32 ac, q_limit_low, q_limit_high, q_limit_low_old, q_limit_high_old;
 	struct sta_info *sta;
 
-	if (count > sizeof(buf))
+	if (count >= sizeof(buf))
 		return -EINVAL;
 
 	if (copy_from_user(buf, user_buf, count))
 		return -EFAULT;
 
-	buf[sizeof(buf) - 1] = 0;
-	len = strlen(buf);
-	if (len > 0 && buf[len - 1] == '\n')
-		buf[len - 1] = 0;
+	if (count && buf[count - 1] == '\n')
+		buf[count - 1] = '\0';
+	else
+		buf[count] = '\0';
 
 	if (sscanf(buf, "%u %u %u", &ac, &q_limit_low, &q_limit_high) != 3)
 		return -EINVAL;
@@ -306,18 +303,17 @@ static ssize_t force_tx_status_write(struct file *file,
 {
 	struct ieee80211_local *local = file->private_data;
 	char buf[3];
-	size_t len;
 
-	if (count > sizeof(buf))
+	if (count >= sizeof(buf))
 		return -EINVAL;
 
 	if (copy_from_user(buf, user_buf, count))
 		return -EFAULT;
 
-	buf[sizeof(buf) - 1] = '\0';
-	len = strlen(buf);
-	if (len > 0 && buf[len - 1] == '\n')
-		buf[len - 1] = 0;
+	if (count && buf[count - 1] == '\n')
+		buf[count - 1] = '\0';
+	else
+		buf[count] = '\0';
 
 	if (buf[0] == '0' && buf[1] == '\0')
 		local->force_tx_status = 0;