[gnome-keyring] egg: Request that secure memory not be dumped to disk

[Daiki Ueno <dueno src gnome org>]

commit e6822428ebfe3b61bfa5df7e04a5e1af7f2048ca
Author: Matthew Garrett <matthewgarrett google com>
Date:   Fri Apr 19 13:08:32 2019 -0700

    egg: Request that secure memory not be dumped to disk
    
    Linux 3.4 added support for the MADV_DONTDUMP option to madvise(), which
    requests that the covered memory not be included in coredumps. It makes
    sense to use this to prevent cases where application crashes could
    result in secrets being persisted to disk or included in dumps that are
    uploaded to remote servers for analysis. I've avoided making this fatal
    since there's a chance this code could be built on systems that have
    MADV_DONTDUMP but run on systems that don't.

 configure.ac            |  8 ++++++++
 egg/egg-secure-memory.c | 13 +++++++++++++
 2 files changed, 21 insertions(+)
---
diff --git a/configure.ac b/configure.ac
index 4b836641..de0c759b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -183,6 +183,14 @@ AC_CHECK_FUNCS(gettimeofday fsync)
 
 AC_CHECK_FUNCS(mlock)
 
+# --------------------------------------------------------------------
+# Prevent memory from being included in core dumps
+#
+
+AC_CHECK_DEFINE([sys/mman.h],[MADV_DONTDUMP],
+  AC_DEFINE([HAVE_MADV_DONTDUMP], [1],
+    [Define if madvise knows about MADV_DONTDUMP]))
+
 # --------------------------------------------------------------------
 # socket()
 #
diff --git a/egg/egg-secure-memory.c b/egg/egg-secure-memory.c
index bc82184a..3dca8fb5 100644
--- a/egg/egg-secure-memory.c
+++ b/egg/egg-secure-memory.c
@@ -885,6 +885,19 @@ sec_acquire_pages (size_t *sz,
 
        DEBUG_ALLOC ("gkr-secure-memory: new block ", *sz);
 
+#if defined(HAVE_MADV_DONTDUMP)
+       if (madvise (pages, *sz, MADV_DONTDUMP) < 0) {
+               if (show_warning && egg_secure_warnings) {
+                       /*
+                        * Not fatal - this was added in Linux 3.4 and older
+                        * kernels will legitimately fail this at runtime
+                        */
+                       fprintf (stderr, "couldn't MADV_DONTDUMP %lu bytes of memory (%s): %s\n",
+                                (unsigned long)*sz, during_tag, strerror (errno));
+               }
+       }
+#endif
+
        show_warning = 1;
        return pages;