os: handle 256 character hostnames

Fix a (rather academic) buffer overflow. MAXHOSTNAMELEN is 256 on most
platforms, which means the buffer wasn't big enough to hold the
trailing nul byte on a system with a maximum length hostname.

src/node_os.cc

@@ -33,7 +33,9 @@
 #endif
 
 #ifdef __POSIX__
+# include <netdb.h>         // MAXHOSTNAMELEN on Solaris.
 # include <unistd.h>        // gethostname, sysconf
+# include <sys/param.h>     // MAXHOSTNAMELEN on Linux and the BSDs.
 # include <sys/utsname.h>
 #endif
 
@@ -51,10 +53,9 @@ static Handle<Value> GetEndianness(const Arguments& args) {
 
 static Handle<Value> GetHostname(const Arguments& args) {
   HandleScope scope;
-  char s[255];
-  int r = gethostname(s, 255);
+  char buf[MAXHOSTNAMELEN + 1];
 
-  if (r < 0) {
+  if (gethostname(buf, sizeof(buf))) {
 #ifdef __POSIX__
     return ThrowException(ErrnoException(errno, "gethostname"));
 #else // __MINGW32__
@@ -62,7 +63,7 @@ static Handle<Value> GetHostname(const Arguments& args) {
 #endif // __MINGW32__
   }
 
-  return scope.Close(String::New(s));
+  return scope.Close(String::New(buf));
 }
 
 static Handle<Value> GetOSType(const Arguments& args) {