[glibc/release/2.30/master] rtld: Check __libc_enable_secure before honoring LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126) [BZ #2520

[glibc/release/2.30/master] rtld: Check __libc_enable_secure before honoring LD_PREFER_MAP_32BIT_EXEC (CVE-2019-19126) [BZ #2520

[Florian Weimer]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain; charset="us-ascii", Size: 2383 bytes --]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=37c90e117310728a4ad1eb998c0bbe7d79c4a398

commit 37c90e117310728a4ad1eb998c0bbe7d79c4a398
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").
    
    (cherry picked from commit d5dfad4326fc683c813df1e37bbf5cf920591c8e)

Diff:
---
 NEWS                                            | 9 +++++++++
 sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h | 3 ++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index c7dcb54..b0d2167 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,14 @@ using `glibc' in the "product" field.
 \f
 Version 2.30.1
 
+Security related changes:
+
+CVE-2019-19126: ld.so failed to ignore the LD_PREFER_MAP_32BIT_EXEC
+  environment variable during program execution after a security
+  transition, allowing local attackers to restrict the possible mapping
+  addresses for loaded libraries and thus bypass ASLR for a setuid
+  program.  Reported by Marcin Kościelnicki.
+
 The following bugs are resolved with this release:
 
   [24682] localedata: zh_CN first weekday should be Monday per GB/T
@@ -15,6 +23,7 @@ The following bugs are resolved with this release:
   [24986] alpha: new getegid, geteuid and getppid syscalls used
     unconditionally
   [25189] Don't use a custom wrapper macro around __has_include
+  [25204] Ignore LD_PREFER_MAP_32BIT_EXEC for SUID programs
 
 \f
 Version 2.30
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;