rng-tools: add patch from upstream to fix rngd (#3442)

"rngd" currently crashes (smashed stack) on 64-bit machines that
support the RDRAND instruction, unless you expicitly disable its use.
This fixes the problem.

srcpkgs/rng-tools/patches/rdrand.patch

@@ -0,0 +1,24 @@
+This patch from upstream (https://github.com/nhorman/rng-tools/commit/f12a80185a4bbf65fbc860f2d2e25af67c70ad6b)
+will allow rngd to run. It can safely be deleted as soon as there is another upstream release.
+
+Without this patch, rngd will die with a "smashed stack" on 64-bit machines that support the RDRAND instruction.
+
+
+--- rngd_rdrand.c.orig	2018-09-25 19:54:05.000000000 +0200
++++ rngd_rdrand.c	2018-10-01 05:42:38.655982555 +0200
+@@ -246,7 +246,14 @@
+ 	if (ent_src->rng_options[DRNG_OPT_AES].int_val)
+ 		return xread_drng_with_aes(buf, size, ent_src);
+ 
+-	x86_rdrand_bytes(buf, size);
++	/* NB: x86_rdrand_bytes might overrun end of buffer, if not a multiple of 8 */
++	if (size > 7)
++		x86_rdrand_bytes(buf, (size&~7));
++	if ((size&7) != 0) {
++		unsigned char tempbuf[8];
++		x86_rdrand_bytes(tempbuf, (size&7));
++		memcpy((unsigned char *)buf+(size&~7), tempbuf, (size&7));
++	}
+ 	return 0;
+ }
+ 

srcpkgs/rng-tools/template

@@ -1,7 +1,7 @@
 # Template file for 'rng-tools'
 pkgname=rng-tools
 version=6.5
-revision=1
+revision=2
 wrksrc=${pkgname}-${version}
 build_style=gnu-configure
 makedepends="libgcrypt-devel libsysfs-devel libcurl-devel libxml2-devel"