[PATCH] server: Avoid deprecated g_memdup

[Eric Blake <eblake@redhat.com>]

glib now recommends that we use g_memdup2() to avoid accidental 32-bit
truncation bugs on platforms where g_size is larger than guint:

https://discourse.gnome.org/t/port-your-module-from-g-memdup-to-g-memdup2-now/5538

and failure to do so causes noisy compilation due to deprecation
warnings with glib 2.68:

nbd-server.c: In function ‘parse_cfile’:
nbd-server.c:1010:25: warning: ‘g_memdup’ is deprecated: Use 'g_memdup2' instead [-Wdeprecated-declarations]
 1010 |                         SERVER *srv = serve_inc_ref(g_memdup(&s, sizeof(SERVER)));
      |                         ^~~~~~
In file included from /usr/include/glib-2.0/glib.h:82,
                 from nbd-server.c:117:
/usr/include/glib-2.0/glib/gstrfuncs.h:257:23: note: declared here
  257 | gpointer              g_memdup         (gconstpointer mem,
      |                       ^~~~~~~~

Of course, we still want to build on platforms with older glib that
lack g_memdup2().  Thankfully, it's easy enough to audit that all our
current uses of g_memdup() do not overflow 32 bits.
---
 configure.ac | 5 +++++
 nbd-server.c | 7 ++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 48ba507..9504899 100644
--- a/configure.ac
+++ b/configure.ac
@@ -292,7 +292,9 @@ AC_CHECK_HEADERS([arpa/inet.h fcntl.h netdb.h netinet/in.h sys/ioctl.h sys/socke
 PKG_CHECK_MODULES(GLIB, [glib-2.0 >= 2.26.0 gthread-2.0 >= 2.26.0], [HAVE_GLIB=yes], AC_MSG_ERROR([Missing glib]))

 my_save_cflags="$CFLAGS"
+my_save_libs="$LIBS"
 CFLAGS="-Wdeprecated-declarations -Werror $GLIB_CFLAGS"
+LIBS="$GLIB_LIBS"
 AC_MSG_CHECKING([if we are using an old glib 2.0 library])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
 	[[#include <glib.h>]],
@@ -306,7 +308,10 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
 		AC_DEFINE(HAVE_OLD_GLIB, 0, [Define to 1 if you have an old glib library])
 	]
 )
+dnl g_memdup2 added in glib-2.68
+AC_CHECK_FUNCS([g_memdup2])
 CFLAGS="$my_save_cflags"
+LIBS="$my_save_libs"

 AC_MSG_CHECKING([whether _BSD_SOURCE needs to be defined for DT_* macros])
 AC_PREPROC_IFELSE(
diff --git a/nbd-server.c b/nbd-server.c
index 0b32bcd..1eff99d 100644
--- a/nbd-server.c
+++ b/nbd-server.c
@@ -154,6 +154,11 @@
 #include <gnutls/x509.h>
 #endif

+#ifndef HAVE_G_MEMDUP2
+/* Our uses of g_memdup2 below are safe from g_memdup's 32-bit overflow */
+#define g_memdup2 g_memdup
+#endif
+
 /** Where our config file actually is */
 gchar* config_file_pos;

@@ -1007,7 +1012,7 @@ GArray* parse_cfile(gchar* f, struct generic_conf *const genconf, bool expect_ge
 		if(i>0 || !expect_generic) {
 			s.servename = groups[i];

-			SERVER *srv = serve_inc_ref(g_memdup(&s, sizeof(SERVER)));
+			SERVER *srv = serve_inc_ref(g_memdup2(&s, sizeof(SERVER)));
 			g_array_append_val(retval, srv);
 		}
 #ifndef WITH_SDP
-- 
2.31.1