From c9cc7dd3d7117bb4a07a09e7ffff4f8d2d612fb1 Mon Sep 17 00:00:00 2001
From: Sebastian Pipping <sebastian@pipping.org>
Date: Thu, 25 May 2017 17:46:42 +0200
Subject: [PATCH] Start using getrandom for entropy extraction with glibc 2.25+

---
 expat/configure.ac   | 17 +++++++++++++++++
 expat/lib/xmlparse.c | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/expat/configure.ac b/expat/configure.ac
index 75b6500f..5ae840fe 100644
--- a/expat/configure.ac
+++ b/expat/configure.ac
@@ -99,6 +99,23 @@ AC_C_CONST
 AC_TYPE_SIZE_T
 AC_CHECK_FUNCS(memmove bcopy)
 
+
+AC_MSG_CHECKING([for getrandom (Linux 3.17+, glibc 2.25+)])
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+  #include <stdlib.h>  /* for NULL */
+  #include <sys/random.h>
+  int main() {
+    return getrandom(NULL, 0U, 0U);
+  }
+])], [
+    AC_DEFINE([HAVE_GETRANDOM], [1],
+        [Define to 1 if you have the `getrandom' function.])
+    AC_MSG_RESULT([yes])
+], [
+    AC_MSG_RESULT([no])
+])
+
+
 dnl Only needed for xmlwf:
 AC_CHECK_HEADERS(fcntl.h unistd.h)
 AC_TYPE_OFF_T
diff --git a/expat/lib/xmlparse.c b/expat/lib/xmlparse.c
index 177b0b5f..af3c7890 100644
--- a/expat/lib/xmlparse.c
+++ b/expat/lib/xmlparse.c
@@ -698,6 +698,36 @@ static const XML_Char implicitContext[] = {
 };
 
 
+#if defined(HAVE_GETRANDOM)
+# include <sys/random.h>
+# include <errno.h>
+
+/* Obtain entropy on Linux 3.17+ with glibc 2.25+ */
+static int
+writeRandomBytes_getrandom(void * target, size_t count) {
+  int success = 0;  /* full count bytes written? */
+  size_t bytesWrittenTotal = 0;
+  const unsigned int getrandomFlags = 0;
+
+  do {
+    void * const currentTarget = (void*)((char*)target + bytesWrittenTotal);
+    const size_t bytesToWrite = count - bytesWrittenTotal;
+
+    const int bytesWrittenMore
+        = getrandom(currentTarget, bytesToWrite, getrandomFlags);
+    if (bytesWrittenMore > 0) {
+      bytesWrittenTotal += bytesWrittenMore;
+      if (bytesWrittenTotal >= count)
+        success = 1;
+    }
+  } while (! success && (errno == EINTR || errno == EAGAIN));
+
+  return success;
+}
+
+#endif  /* defined(HAVE_GETRANDOM) */
+
+
 #ifdef _WIN32
 
 typedef BOOLEAN (APIENTRY *RTLGENRANDOM_FUNC)(PVOID, ULONG);
@@ -774,6 +804,10 @@ generate_hash_secret_salt(XML_Parser parser)
   if (writeRandomBytes_RtlGenRandom((void *)&entropy, sizeof(entropy))) {
     return entropy;
   }
+#elif defined(HAVE_GETRANDOM)
+  if (writeRandomBytes_getrandom((void *)&entropy, sizeof(entropy))) {
+    return entropy;
+  }
 #endif
   /* .. and self-made low quality for backup: */