ldso: let people disable to lookup into LD_LIBRARY_PATH

On hardened system it could be useful to disable the use
of LD_LIBRARY_PATH.

Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>

extra/Configs/Config.in

@@ -409,6 +409,17 @@ config LDSO_SEARCH_INTERP_PATH
 
 	  If unsure, simply say Y here.
 
+config LDSO_LD_LIBRARY_PATH
+	bool "Add LD_LIBRARY_PATH to lib search path"
+	depends on HAVE_SHARED
+	default y
+	help
+	  On hardened system it could be useful to disable the use of
+	  LD_LIBRARY_PATH environment variable (a colon-separated list of
+	  directories in which to search for ELF libraries at execution-time).
+
+	  If unsure, simply say Y here.
+
 config LDSO_NO_CLEANUP
 	bool "Disable automatic unloading of dynamically loaded shared objects"
 	depends on HAVE_SHARED

ldso/ldso/dl-elf.c

@@ -236,6 +236,7 @@ struct elf_resolve *_dl_load_shared_library(int secure, struct dyn_elf **rpnt,
 	}
 #endif
 
+#ifdef __LDSO_LD_LIBRARY_PATH__
 	/* Check in LD_{ELF_}LIBRARY_PATH, if specified and allowed */
 	if (_dl_library_path) {
 		_dl_if_debug_dprint("\tsearching LD_LIBRARY_PATH='%s'\n", _dl_library_path);
@@ -244,7 +245,7 @@ struct elf_resolve *_dl_load_shared_library(int secure, struct dyn_elf **rpnt,
 			return tpnt1;
 		}
 	}
-
+#endif
 	/*
 	 * The ABI specifies that RUNPATH is searched after LD_LIBRARY_PATH.
 	 */

ldso/ldso/ldso.c

@@ -46,7 +46,9 @@
 #include LDSO_ELFINTERP
 
 /* Global variables used within the shared library loader */
+#ifdef __LDSO_LD_LIBRARY_PATH__
 char *_dl_library_path         = NULL;	/* Where we look for libraries */
+#endif
 #ifdef __LDSO_PRELOAD_ENV_SUPPORT__
 char *_dl_preload              = NULL;	/* Things to be loaded before the libs */
 #endif
@@ -457,7 +459,9 @@ void *_dl_get_ready_to_run(struct elf_resolve *tpnt, DL_LOADADDR_TYPE load_addr,
 #ifdef __LDSO_PRELOAD_ENV_SUPPORT__
 		_dl_preload = _dl_getenv("LD_PRELOAD", envp);
 #endif
+#ifdef __LDSO_LD_LIBRARY_PATH__
 		_dl_library_path = _dl_getenv("LD_LIBRARY_PATH", envp);
+#endif
 	} else {
 		static const char unsecure_envvars[] =
 #ifdef EXTRA_UNSECURE_ENVVARS
@@ -476,7 +480,9 @@ void *_dl_get_ready_to_run(struct elf_resolve *tpnt, DL_LOADADDR_TYPE load_addr,
 #ifdef __LDSO_PRELOAD_ENV_SUPPORT__
 		_dl_preload = NULL;
 #endif
+#ifdef __LDSO_LD_LIBRARY_PATH__
 		_dl_library_path = NULL;
+#endif
 		/* SUID binaries can be exploited if they do LAZY relocation. */
 		unlazy = RTLD_NOW;
 	}
@@ -494,7 +500,9 @@ void *_dl_get_ready_to_run(struct elf_resolve *tpnt, DL_LOADADDR_TYPE load_addr,
 		tpnt->libname = argv[0];
 		while (argc > 1)
 			if (! _dl_strcmp (argv[1], "--library-path") && argc > 2) {
+#ifdef __LDSO_LD_LIBRARY_PATH__
 				_dl_library_path = argv[2];
+#endif
 				_dl_skip_args += 2;
 				argc -= 2;
 				argv += 2;

ldso/libdl/libdl.c

@@ -100,7 +100,9 @@ int   _dl_debug_file      = 2;
 const char *_dl_progname       = "";        /* Program name */
 void *(*_dl_malloc_function)(size_t);
 void (*_dl_free_function) (void *p);
+#ifdef __LDSO_LD_LIBRARY_PATH__
 char *_dl_library_path         = NULL;         /* Where we look for libraries */
+#endif
 int _dl_errno                  = 0;         /* We can't use the real errno in ldso */
 size_t _dl_pagesize            = PAGE_SIZE; /* Store the page size for use later */
 /* This global variable is also to communicate with debuggers such as gdb. */
@@ -368,7 +370,7 @@ void *dlopen(const char *libname, int flag)
 	if (getenv("LD_BIND_NOW"))
 		now_flag = RTLD_NOW;
 
-#ifndef SHARED
+#if !defined SHARED && defined __LDSO_LIBRARY_PATH__
 	/* When statically linked, the _dl_library_path is not yet initialized */
 	_dl_library_path = getenv("LD_LIBRARY_PATH");
 #endif