From 37c90e117310728a4ad1eb998c0bbe7d79c4a398 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Marcin=20Ko=C5=9Bcielnicki?= <mwk@0x04.net>
Date: Thu, 21 Nov 2019 00:20:15 +0100
Subject: [PATCH] rtld: Check __libc_enable_secure before honoring
 LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126) [BZ #25204]

The problem was introduced in glibc 2.23, in commit
b9eb92ab05204df772eb4929eccd018637c9f3e9
("Add Prefer_MAP_32BIT_EXEC to map executable pages with MAP_32BIT").

(cherry picked from commit d5dfad4326fc683c813df1e37bbf5cf920591c8e)

Upstream-Status: Backport [https://sourceware.org/git/gitweb.cgi?p=glibc.git;a=commit;h=37c90e117310728a4ad1eb998c0bbe7d79c4a398]
CVE: CVE-2019-19126
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>
---
diff --git a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
index 975cbe2..df2cdfd 100644
--- a/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
+++ b/sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h
@@ -31,7 +31,8 @@
    environment variable, LD_PREFER_MAP_32BIT_EXEC.  */
 #define EXTRA_LD_ENVVARS \
   case 21:								  \
-    if (memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0)		  \
+    if (!__libc_enable_secure						  \
+	&& memcmp (envline, "PREFER_MAP_32BIT_EXEC", 21) == 0)		  \
       GLRO(dl_x86_cpu_features).feature[index_arch_Prefer_MAP_32BIT_EXEC] \
 	|= bit_arch_Prefer_MAP_32BIT_EXEC;				  \
     break;
-- 
2.9.3