Support LAUNCHD code on Linux. Enable by default. [v2]

The launchd code allows $DISPLAY to be set to any path name, which
allows placing the X connection socket in a more secure location in
the filesystem than /tmp.

This is intended to help fix the security issue raised here:

    https://www.openwall.com/lists/oss-security/2020/11/09/3
    https://lists.x.org/archives/xorg-devel/2020-November/058626.html

Signed-off-by: Keith Packard <keithp@keithp.com>

----

v2
	Make internal version of strlcpy static so that we don't
	publish this name to applications

configure.ac

@@ -173,6 +173,15 @@ dnl check for support for Solaris Trusted Extensions
 AC_CHECK_HEADERS([tsol/label.h])
 AC_CHECK_FUNCS([is_system_labeled])
 
+dnl check for strlcpy
+AC_SEARCH_LIBS(strlcpy, [bsd], [AC_DEFINE(HAVE_STRLCPY, 1, [strlcpy() function is available])],)
+
+case "$LIBS" in
+	*-lbsd*)
+		AC_DEFINE(HAVE_LIBBSD, 1, [use -lbsd for bsd string functions])
+		;;
+esac	
+
 dnl check for IOV_MAX, and fall back to UIO_MAXIOV on BSDish systems
 AC_CHECK_DECL([IOV_MAX], [],
               [AC_CHECK_DECL([UIO_MAXIOV], [AC_DEFINE([IOV_MAX], [UIO_MAXIOV])],
@@ -247,7 +256,7 @@ XCB_EXTENSION(XTest, yes)
 XCB_EXTENSION(Xv, yes)
 XCB_EXTENSION(XvMC, yes)
 
-AC_ARG_WITH(launchd, AS_HELP_STRING([--with-launchd], [Build with support for Apple's launchd (default: auto)]), [LAUNCHD=$withval], [LAUNCHD=auto])
+AC_ARG_WITH(launchd, AS_HELP_STRING([--with-launchd], [Build with support for Apple's launchd (default: auto)]), [LAUNCHD=$withval], [LAUNCHD=yes])
 if test "x$LAUNCHD" = xauto; then
         unset LAUNCHD
         AC_CHECK_PROG(LAUNCHD, [launchd], [yes], [no], [$PATH$PATH_SEPARATOR/sbin])

src/Makefile.am

@@ -5,7 +5,7 @@ EXTSOURCES =	xproto.c \
 		xc_misc.c
 
 AM_CFLAGS = $(BASE_CFLAGS) $(NEEDED_CFLAGS) $(XDMCP_CFLAGS)
-libxcb_la_LIBADD = $(NEEDED_LIBS) $(XDMCP_LIBS)
+libxcb_la_LIBADD = $(LIBS) $(NEEDED_LIBS) $(XDMCP_LIBS)
 libxcb_la_SOURCES = \
 		xcb_conn.c xcb_out.c xcb_in.c xcb_ext.c xcb_xid.c \
 		xcb_list.c xcb_util.c xcb_auth.c c_client.py

src/strlcpy.c

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 1998 Todd C. Miller <Todd.Miller@courtesan.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND TODD C. MILLER DISCLAIMS ALL
+ * WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL TODD C. MILLER BE LIABLE
+ * FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*
+ * Copy src to string dst of size siz.  At most siz-1 characters
+ * will be copied.  Always NUL terminates (unless siz == 0).
+ * Returns strlen(src); if retval >= siz, truncation occurred.
+ */
+static size_t
+xcb_strlcpy(char *dst, const char *src, size_t siz)
+{
+    register char *d = dst;
+    register const char *s = src;
+    register size_t n = siz;
+
+    /* Copy as many bytes as will fit */
+    if (n != 0 && --n != 0) {
+        do {
+            if ((*d++ = *s++) == 0)
+                break;
+        } while (--n != 0);
+    }
+
+    /* Not enough room in dst, add NUL and traverse rest of src */
+    if (n == 0) {
+        if (siz != 0)
+            *d = '\0';          /* NUL-terminate dst */
+        while (*s++);
+    }
+
+    return s - src - 1;         /* count does not include NUL */
+}

src/xcb_util.c

@@ -83,6 +83,16 @@ int xcb_sumof(uint8_t *list, int len)
 }
 
 #ifdef HAVE_LAUNCHD
+
+#ifdef HAVE_STRLCPY
+# ifdef HAVE_LIBBSD
+#  include <bsd/string.h> /* for strlcpy */
+# endif
+# define xcb_strlcpy(dst, src, size) strlcpy(dst, src, size)
+#else
+# include "strlcpy.c"
+#endif
+
 /* Return true and parse if name matches <path to socket>[.<screen>]
  * Upon success:
  *     host = <path to socket>
@@ -97,7 +107,7 @@ static int _xcb_parse_display_path_to_socket(const char *name, char **host, char
     char path[PATH_MAX];
     int _screen = 0;
 
-    strlcpy(path, name, sizeof(path));
+    xcb_strlcpy(path, name, sizeof(path));
     if (0 != stat(path, &sbuf)) {
         char *dot = strrchr(path, '.');
         if (!dot)
@@ -230,6 +240,9 @@ static int _xcb_open(const char *host, char *protocol, const int display)
     static const char unix_base[] = "/usr/spool/sockets/X11/";
 #else
     static const char unix_base[] = "/tmp/.X11-unix/X";
+#endif
+#ifdef HAVE_LAUNCHD
+    struct stat sbuf;
 #endif
     const char *base = unix_base;
     size_t filelen;
@@ -262,7 +275,6 @@ static int _xcb_open(const char *host, char *protocol, const int display)
 #endif
 
 #ifdef HAVE_LAUNCHD
-    struct stat sbuf;
     if (0 == stat(host, &sbuf)) {
         file = strdup(host);
         if(file == NULL)