elf: Always set l in _dl_init_paths (bug 23462)

After d1d5471579eb0426671bf94f2d71e61dfb204c30 ("Remove dead
DL_DST_REQ_STATIC code.") we always setup the link map l to make the
static and shared cases the same.  The bug is that in elf/dl-load.c
(_dl_init_paths) we conditionally set l only in the #ifdef SHARED
case, but unconditionally use it later.  The simple solution is to
remove the #ifdef SHARED conditional, because it's no longer needed,
and unconditionally setup l for both the static and shared cases. A
regression test is added to run a static binary with
LD_LIBRARY_PATH='$ORIGIN' which crashes before the fix and runs after
the fix.

Co-Authored-By: Florian Weimer <fweimer@redhat.com>

3 files changed, 65 insertions, 35 deletions

diff --git a/elf/Makefile b/elf/Makefile
index b06bf6c..4c9e63d 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -164,7 +164,8 @@ tests-static-normal := tst-leaks1-static tst-array1-static tst-array5-static \
 	       tst-dl-iter-static \
 	       tst-tlsalign-static tst-tlsalign-extern-static \
 	       tst-linkall-static tst-env-setuid tst-env-setuid-tunables \
-	       tst-single_threaded-static tst-single_threaded-pthread-static
+	       tst-single_threaded-static tst-single_threaded-pthread-static \
+	       tst-dst-static
 
 tests-static-internal := tst-tls1-static tst-tls2-static \
 	       tst-ptrguard1-static tst-stackguard1-static \
@@ -1904,3 +1905,5 @@ $(objpfx)list-tunables.out: tst-rtld-list-tunables.sh $(objpfx)ld.so
 	cmp tst-rtld-list-tunables.exp \
 	    $(objpfx)/tst-rtld-list-tunables.out > $@; \
 	$(evaluate-test)
+
+tst-dst-static-ENV = LD_LIBRARY_PATH='$$ORIGIN'
diff --git a/elf/dl-load.c b/elf/dl-load.c
index 9e2089c..376a2e6 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -758,50 +758,45 @@ _dl_init_paths (const char *llp, const char *source,
   max_dirnamelen = SYSTEM_DIRS_MAX_LEN;
   *aelem = NULL;
 
-#ifdef SHARED
   /* This points to the map of the main object.  */
   l = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
-  if (l != NULL)
+  assert (l->l_type != lt_loaded);
+
+  if (l->l_info[DT_RUNPATH])
+    {
+      /* Allocate room for the search path and fill in information
+	 from RUNPATH.  */
+      decompose_rpath (&l->l_runpath_dirs,
+		       (const void *) (D_PTR (l, l_info[DT_STRTAB])
+				       + l->l_info[DT_RUNPATH]->d_un.d_val),
+		       l, "RUNPATH");
+      /* During rtld init the memory is allocated by the stub malloc,
+	 prevent any attempt to free it by the normal malloc.  */
+      l->l_runpath_dirs.malloced = 0;
+
+      /* The RPATH is ignored.  */
+      l->l_rpath_dirs.dirs = (void *) -1;
+    }
+  else
     {
-      assert (l->l_type != lt_loaded);
+      l->l_runpath_dirs.dirs = (void *) -1;
 
-      if (l->l_info[DT_RUNPATH])
+      if (l->l_info[DT_RPATH])
 	{
 	  /* Allocate room for the search path and fill in information
-	     from RUNPATH.  */
-	  decompose_rpath (&l->l_runpath_dirs,
+	     from RPATH.  */
+	  decompose_rpath (&l->l_rpath_dirs,
 			   (const void *) (D_PTR (l, l_info[DT_STRTAB])
-					   + l->l_info[DT_RUNPATH]->d_un.d_val),
-			   l, "RUNPATH");
-	  /* During rtld init the memory is allocated by the stub malloc,
-	     prevent any attempt to free it by the normal malloc.  */
-	  l->l_runpath_dirs.malloced = 0;
-
-	  /* The RPATH is ignored.  */
-	  l->l_rpath_dirs.dirs = (void *) -1;
+					   + l->l_info[DT_RPATH]->d_un.d_val),
+			   l, "RPATH");
+	  /* During rtld init the memory is allocated by the stub
+	     malloc, prevent any attempt to free it by the normal
+	     malloc.  */
+	  l->l_rpath_dirs.malloced = 0;
 	}
       else
-	{
-	  l->l_runpath_dirs.dirs = (void *) -1;
-
-	  if (l->l_info[DT_RPATH])
-	    {
-	      /* Allocate room for the search path and fill in information
-		 from RPATH.  */
-	      decompose_rpath (&l->l_rpath_dirs,
-			       (const void *) (D_PTR (l, l_info[DT_STRTAB])
-					       + l->l_info[DT_RPATH]->d_un.d_val),
-			       l, "RPATH");
-	      /* During rtld init the memory is allocated by the stub
-		 malloc, prevent any attempt to free it by the normal
-		 malloc.  */
-	      l->l_rpath_dirs.malloced = 0;
-	    }
-	  else
-	    l->l_rpath_dirs.dirs = (void *) -1;
-	}
+	l->l_rpath_dirs.dirs = (void *) -1;
     }
-#endif	/* SHARED */
 
   if (llp != NULL && *llp != '\0')
     {
diff --git a/elf/tst-dst-static.c b/elf/tst-dst-static.c
new file mode 100644
index 0000000..56eb371
--- /dev/null
+++ b/elf/tst-dst-static.c
@@ -0,0 +1,32 @@
+/* Test DST expansion for static binaries doesn't carsh.  Bug 23462.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+/* The purpose of this test is to exercise the code in elf/dl-loac.c
+   (_dl_init_paths) or thereabout and ensure that static binaries
+   don't crash when expanding DSTs.
+
+   If the dynamic loader code linked into the static binary cannot
+   handle expanding the DSTs e.g. null-deref on an incomplete link
+   map, then it will crash before reaching main, so the test harness
+   is unnecessary.  */
+
+int
+main (void)
+{
+  return 0;
+}