net: caif: 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().

Cc: "David S . Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/caif/caif_spi.c

@@ -141,29 +141,29 @@ static ssize_t dbgfs_state(struct file *file, char __user *user_buf,
 		return 0;
 
 	/* Print out debug information. */
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"CAIF SPI debug information:\n");
-
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len), FLAVOR);
-
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"STATE: %d\n", cfspi->dbg_state);
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Previous CMD: 0x%x\n", cfspi->pcmd);
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Current CMD: 0x%x\n", cfspi->cmd);
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Previous TX len: %d\n", cfspi->tx_ppck_len);
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Previous RX len: %d\n", cfspi->rx_ppck_len);
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Current TX len: %d\n", cfspi->tx_cpck_len);
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Current RX len: %d\n", cfspi->rx_cpck_len);
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Next TX len: %d\n", cfspi->tx_npck_len);
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Next RX len: %d\n", cfspi->rx_npck_len);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "CAIF SPI debug information:\n");
+
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len), FLAVOR);
+
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "STATE: %d\n", cfspi->dbg_state);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Previous CMD: 0x%x\n", cfspi->pcmd);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Current CMD: 0x%x\n", cfspi->cmd);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Previous TX len: %d\n", cfspi->tx_ppck_len);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Previous RX len: %d\n", cfspi->rx_ppck_len);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Current TX len: %d\n", cfspi->tx_cpck_len);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Current RX len: %d\n", cfspi->rx_cpck_len);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Next TX len: %d\n", cfspi->tx_npck_len);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Next RX len: %d\n", cfspi->rx_npck_len);
 
 	if (len > DEBUGFS_BUF_SIZE)
 		len = DEBUGFS_BUF_SIZE;
@@ -180,23 +180,23 @@ static ssize_t print_frame(char *buf, size_t size, char *frm,
 	int len = 0;
 	int i;
 	for (i = 0; i < count; i++) {
-		len += snprintf((buf + len), (size - len),
+		len += scnprintf((buf + len), (size - len),
 					"[0x" BYTE_HEX_FMT "]",
 					frm[i]);
 		if ((i == cut) && (count > (cut * 2))) {
 			/* Fast forward. */
 			i = count - cut;
-			len += snprintf((buf + len), (size - len),
-					"--- %zu bytes skipped ---\n",
-					count - (cut * 2));
+			len += scnprintf((buf + len), (size - len),
+					 "--- %zu bytes skipped ---\n",
+					 count - (cut * 2));
 		}
 
 		if ((!(i % 10)) && i) {
-			len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-					"\n");
+			len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+					 "\n");
 		}
 	}
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len), "\n");
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len), "\n");
 	return len;
 }
 
@@ -214,18 +214,18 @@ static ssize_t dbgfs_frame(struct file *file, char __user *user_buf,
 		return 0;
 
 	/* Print out debug information. */
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Current frame:\n");
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Current frame:\n");
 
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Tx data (Len: %d):\n", cfspi->tx_cpck_len);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Tx data (Len: %d):\n", cfspi->tx_cpck_len);
 
 	len += print_frame((buf + len), (DEBUGFS_BUF_SIZE - len),
 			   cfspi->xfer.va_tx[0],
 			   (cfspi->tx_cpck_len + SPI_CMD_SZ), 100);
 
-	len += snprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
-			"Rx data (Len: %d):\n", cfspi->rx_cpck_len);
+	len += scnprintf((buf + len), (DEBUGFS_BUF_SIZE - len),
+			 "Rx data (Len: %d):\n", cfspi->rx_cpck_len);
 
 	len += print_frame((buf + len), (DEBUGFS_BUF_SIZE - len),
 			   cfspi->xfer.va_rx,