staging: usbip: fix potential segfault because of unchecked return value of strchr.

This doesn't happen with the usbip virtual hci module, but another
module wanting to interface with this user space code could cause a
seg-fault by sending data without newlines.
Signed-off-by: NChristopher Harvey <charvey@matrox.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/usbip/userspace/libsrc/vhci_driver.c

@@ -59,7 +59,10 @@ static int parse_status(char *value)
 
 
 	/* skip a header line */
-	c = strchr(value, '\n') + 1;
+	c = strchr(value, '\n');
+	if (!c)
+		return -1;
+	c++;
 
 	while (*c != '\0') {
 		int port, status, speed, devid;
@@ -109,7 +112,10 @@ static int parse_status(char *value)
 
 
 		/* go to the next line */
-		c = strchr(c, '\n') + 1;
+		c = strchr(c, '\n');
+		if (!c)
+			break;
+		c++;
 	}
 
 	dbg("exit");
@@ -264,11 +270,17 @@ static int get_nports(void)
 	    attr_status->method, attr_status->value);
 
 	/* skip a header line */
-	c = strchr(attr_status->value, '\n') + 1;
+	c = strchr(attr_status->value, '\n');
+	if (!c)
+		return 0;
+	c++;
 
 	while (*c != '\0') {
 		/* go to the next line */
-		c = strchr(c, '\n') + 1;
+		c = strchr(c, '\n');
+		if (!c)
+			return nports;
+		c++;
 		nports += 1;
 	}