[syslog] Strip invalid characters from hostname

Avoid generating syntactically invalid log messages by ensuring that
invalid characters are not present in the hostname.  In particular,
ensure that any whitespace is stripped, since whitespace functions as
a field separator for syslog messages.

Reported-by: Alex Davies <adavies@jumptrading.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/udp/syslog.c

@@ -27,6 +27,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 
 #include <stdint.h>
 #include <stdlib.h>
+#include <ctype.h>
 #include <byteswap.h>
 #include <ipxe/xfer.h>
 #include <ipxe/open.h>
@@ -91,15 +92,15 @@ static char *syslog_domain;
  */
 int syslog_send ( struct interface *xfer, unsigned int severity,
 		  const char *message, const char *terminator ) {
+	const char *hostname = ( syslog_hostname ? syslog_hostname : "" );
+	const char *domain = ( ( hostname[0] && syslog_domain ) ?
+			       syslog_domain : "" );
 
 	return xfer_printf ( xfer, "<%d>%s%s%s%sipxe: %s%s",
 			     SYSLOG_PRIORITY ( SYSLOG_DEFAULT_FACILITY,
-					       severity ),
-			     ( syslog_hostname ? syslog_hostname : "" ),
-			     ( syslog_domain ? "." : "" ),
-			     ( syslog_domain ? syslog_domain : "" ),
-			     ( ( syslog_hostname || syslog_domain ) ? " " : ""),
-			     message, terminator );
+					       severity ), hostname,
+			     ( domain[0] ? "." : "" ), domain,
+			     ( hostname[0] ? " " : "" ), message, terminator );
 }
 
 /******************************************************************************
@@ -211,6 +212,28 @@ const struct setting syslog6_setting __setting ( SETTING_MISC, syslog6 ) = {
 	.scope = &ipv6_scope,
 };
 
+/**
+ * Strip invalid characters from host/domain name
+ *
+ * @v name		Name to strip
+ */
+static void syslog_fix_name ( char *name ) {
+	char *fixed = name;
+	int c;
+
+	/* Do nothing if name does not exist */
+	if ( ! name )
+		return;
+
+	/* Strip any non-printable or whitespace characters from the name */
+	do {
+		c = *(name++);
+		*fixed = c;
+		if ( isprint ( c ) && ! isspace ( c ) )
+			fixed++;
+	} while ( c );
+}
+
 /**
  * Apply syslog settings
  *
@@ -223,8 +246,10 @@ static int apply_syslog_settings ( void ) {
 	/* Fetch hostname and domain name */
 	free ( syslog_hostname );
 	fetch_string_setting_copy ( NULL, &hostname_setting, &syslog_hostname );
+	syslog_fix_name ( syslog_hostname );
 	free ( syslog_domain );
 	fetch_string_setting_copy ( NULL, &domain_setting, &syslog_domain );
+	syslog_fix_name ( syslog_domain );
 
 	/* Fetch log server */
 	syslog_console.disabled = CONSOLE_DISABLED;