staging: rtl8192e: Use scnprintf() for avoiding potential buffer overflow

Since snprintf() returns the would-be-output size instead of the
actual output size, the succeeding calls may go beyond the given
buffer limit.  Fix it by replacing with scnprintf().
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20200311092451.23933-3-tiwai@suse.deSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192e/rtllib_rx.c

@@ -2092,7 +2092,7 @@ int rtllib_parse_info_param(struct rtllib_device *ieee,
 						 MAX_RATES_LENGTH);
 			for (i = 0; i < network->rates_len; i++) {
 				network->rates[i] = info_element->data[i];
-				p += snprintf(p, sizeof(rates_str) -
+				p += scnprintf(p, sizeof(rates_str) -
 					      (p - rates_str), "%02X ",
 					      network->rates[i]);
 				if (rtllib_is_ofdm_rate
@@ -2120,7 +2120,7 @@ int rtllib_parse_info_param(struct rtllib_device *ieee,
 						    MAX_RATES_EX_LENGTH);
 			for (i = 0; i < network->rates_ex_len; i++) {
 				network->rates_ex[i] = info_element->data[i];
-				p += snprintf(p, sizeof(rates_str) -
+				p += scnprintf(p, sizeof(rates_str) -
 					      (p - rates_str), "%02X ",
 					      network->rates_ex[i]);
 				if (rtllib_is_ofdm_rate

drivers/staging/rtl8192e/rtllib_wx.c

@@ -114,7 +114,7 @@ static inline char *rtl819x_translate_scan(struct rtllib_device *ieee,
 	/* Add basic and extended rates */
 	max_rate = 0;
 	p = custom;
-	p += snprintf(p, MAX_CUSTOM_LEN - (p - custom), " Rates (Mb/s): ");
+	p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom), " Rates (Mb/s): ");
 	for (i = 0, j = 0; i < network->rates_len;) {
 		if (j < network->rates_ex_len &&
 		    ((network->rates_ex[j] & 0x7F) <
@@ -124,12 +124,12 @@ static inline char *rtl819x_translate_scan(struct rtllib_device *ieee,
 			rate = network->rates[i++] & 0x7F;
 		if (rate > max_rate)
 			max_rate = rate;
-		p += snprintf(p, MAX_CUSTOM_LEN - (p - custom),
+		p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom),
 			      "%d%s ", rate >> 1, (rate & 1) ? ".5" : "");
 	}
 	for (; j < network->rates_ex_len; j++) {
 		rate = network->rates_ex[j] & 0x7F;
-		p += snprintf(p, MAX_CUSTOM_LEN - (p - custom),
+		p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom),
 			      "%d%s ", rate >> 1, (rate & 1) ? ".5" : "");
 		if (rate > max_rate)
 			max_rate = rate;
@@ -226,7 +226,7 @@ static inline char *rtl819x_translate_scan(struct rtllib_device *ieee,
 	 */
 	iwe.cmd = IWEVCUSTOM;
 	p = custom;
-	p += snprintf(p, MAX_CUSTOM_LEN - (p - custom),
+	p += scnprintf(p, MAX_CUSTOM_LEN - (p - custom),
 		      " Last beacon: %lums ago",
 		      (jiffies - network->last_scanned) / (HZ / 100));
 	iwe.u.data.length = p - custom;