From 378397fc612b96d9cd6731db2725aa927d6331ad Mon Sep 17 00:00:00 2001
From: Marcin Kościelnicki <mwk@0x04.net>
Date: Mon, 9 Dec 2019 12:28:41 -0800
Subject: [PATCH] rtld: Check __libc_enable_secure before honoring
 LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126)

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)
---
 sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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 194369174d..e7f0373a70 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;
-- 
2.24.0.393.g34dc348eaf-goog