commit d5dfad4326fc683c813df1e37bbf5cf920591c8e

Author: Marcin Kościelnicki <mwk@0x04.net>

Date:   Thu Nov 21 00:20:15 2019 +0100

    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").

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 194369174df08946..ac694c032e7baf87 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;