[2.25 COMMITTED] CVE-2017-1000366: Ignore LD_LIBRARY_PATH for AT_SECURE=1 programs [BZ #21624]

[Florian Weimer]

LD_LIBRARY_PATH can only be used to reorder system search paths, which
is not useful functionality.

This makes an exploitable unbounded alloca in _dl_init_paths unreachable
for AT_SECURE=1 programs.

(cherry picked from commit f6110a8fee2ca36f8e2d2abecf3cba9fa7b8ea7d)

2017-06-19  Florian Weimer  <fweimer@redhat.com>

	[BZ #21624]
	CVE-2017-1000366
	* elf/rtld.c (process_envvars): Ignore LD_LIBRARY_PATH for
	__libc_enable_secure.

diff --git a/NEWS b/NEWS
index d528723..29079e8 100644
--- a/NEWS
+++ b/NEWS
@@ -15,6 +15,7 @@ The following bugs are resolved with this release:
   [21115] sunrpc: Use-after-free in error path in clntudp_call
   [21289] Fix symbol redirect for fts_set
   [21386] Assertion in fork for distinct parent PID is incorrect
+  [21624] Unsafe alloca allows local attackers to alias stack and heap (CVE-2017-1000366)
 
 Version 2.25
 
diff --git a/elf/rtld.c b/elf/rtld.c
index a036ece..2fc33a6 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -2418,7 +2418,8 @@ process_envvars (enum mode *modep)
 
 	case 12:
 	  /* The library search path.  */
-	  if (memcmp (envline, "LIBRARY_PATH", 12) == 0)
+	  if (!__libc_enable_secure
+	      && memcmp (envline, "LIBRARY_PATH", 12) == 0)
 	    {
 	      library_path = &envline[13];
 	      break;