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authorMarcin Koƛcielnicki <mwk@0x04.net>2019-11-21 00:20:15 +0100
committerFlorian Weimer <fweimer@redhat.com>2019-11-21 12:56:44 +0100
commitd5dfad4326fc683c813df1e37bbf5cf920591c8e (patch)
treecaf191d9e8e3dc6f42b0b5e2a04370ecc2858198
parent2a764c6ee848dfe92cb2921ed3b14085f15d9e79 (diff)
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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").
-rw-r--r--NEWS6
-rw-r--r--sysdeps/unix/sysv/linux/x86_64/64/dl-librecon.h3
2 files changed, 7 insertions, 2 deletions
diff --git a/NEWS b/NEWS
index 50479f17c9..df03f4dc48 100644
--- a/NEWS
+++ b/NEWS
@@ -86,7 +86,11 @@ Changes to build and runtime requirements:
 
 Security related changes:
 
-  [Add security related changes here]
+  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 Koƛcielnicki.
 
 The following bugs are resolved with this release:
 
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 0e95221908..e3af239faa 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;