fix: harden the per-user IPC endpoint

srv.c

@@ -1,7 +1,10 @@
 #include "dat.h"
 #include "fn.h"
 
-static char adir[40];
+#include <sys/stat.h>
+#include <sys/un.h>
+
+static char adir[256];
 static Channel *clientc;
 
 typedef struct Client Client;
@@ -71,12 +74,16 @@ clientthread(void *arg)
 static void
 srvinit(void)
 {
-	char addr[64];
+	char addr[128], path[sizeof(((struct sockaddr_un*)0)->sun_path)];
 
-	snprint(addr, sizeof(addr), "unix!" IPCPATH, getuid());
-	remove(addr + 5);
+	if(ipcpath(path, sizeof path) < 0)
+		die("IPC path is too long");
+	if(snprint(addr, sizeof addr, "unix!%s", path) >= (int)sizeof addr)
+		die("IPC address is too long");
 	if(announce(addr, adir) < 0)
-		die("announce: %r");
+		die("IPC endpoint is already in use: %r");
+	if(chmod(path, 0600) < 0)
+		die("can't protect IPC endpoint: %s", path);
 }
 
 void