elf: Self-dlopen failure with explict loader invocation [BZ #24900]

In case of an explicit loader invocation, ld.so essentially performs
a dlopen call to load the main executable.  Since the pathname of
the executable is known at this point, it gets stored in the link
map.  In regular mode, the pathname is not known and "" is used
instead.

As a result, if a program calls dlopen on the pathname of the main
program, the dlopen call succeeds and returns a handle for the main
map.  This results in an unnecessary difference between glibc
testing (without --enable-hardcoded-path-in-tests) and production
usage.

This commit discards the names when building the link map in
_dl_new_object for the main executable, but it still determines
the origin at this point in case of an explict loader invocation.
The reason is that the specified pathname has to be used; the kernel
has a different notion of the main executable.

1 files changed, 30 insertions, 17 deletions

diff --git a/elf/tst-dlopen-aout.c b/elf/tst-dlopen-aout.c
index 25cfe2f740..3e39fc6067 100644
--- a/elf/tst-dlopen-aout.c
+++ b/elf/tst-dlopen-aout.c
@@ -1,7 +1,8 @@
-/* Test case for BZ #16634.
+/* Test case for BZ #16634 and BZ#24900.
 
    Verify that incorrectly dlopen()ing an executable without
-   __RTLD_OPENEXEC does not cause assertion in ld.so.
+   __RTLD_OPENEXEC does not cause assertion in ld.so, and that it
+   actually results in an error.
 
    Copyright (C) 2014-2019 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
@@ -24,6 +25,8 @@
 #include <pthread.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
 #include <support/support.h>
 #include <support/xthread.h>
 
@@ -35,28 +38,35 @@ fn (void *p)
   return p;
 }
 
+/* Call dlopen on PATH and check that fails with an error message
+   indicating an attempt to open an ET_EXEC or PIE object.  */
+static void
+check_dlopen_failure (const char *path)
+{
+  void *handle = dlopen (path, RTLD_LAZY);
+  if (handle != NULL)
+    FAIL_EXIT1 ("dlopen succeeded unexpectedly: %s", path);
+
+  const char *message = dlerror ();
+  TEST_VERIFY_EXIT (message != NULL);
+  if ((strstr (message,
+	       "cannot dynamically load position-independent executable")
+       == NULL)
+      && strstr (message, "cannot dynamically load executable") == NULL)
+    FAIL_EXIT1 ("invalid dlopen error message: \"%s\"", message);
+}
+
 static int
 do_test (int argc, char *argv[])
 {
   int j;
 
-  /* Use the full path so that the dynamic loader does not recognize
-     the main program as already loaded (even with an explicit ld.so
-     invocation).  */
-  char *path = xasprintf ("%s/%s", support_objdir_root, "tst-dlopen-aout");
-  printf ("info: dlopen object: %s\n", path);
-
   for (j = 0; j < 100; ++j)
     {
       pthread_t thr;
-      void *p;
-
-      p = dlopen (path, RTLD_LAZY);
-      if (p != NULL)
-        {
-          puts ("error: dlopen succeeded unexpectedly");
-          return 1;
-        }
+
+      check_dlopen_failure (argv[0]);
+
       /* We create threads to force TLS allocation, which triggers
 	 the original bug i.e. running out of surplus slotinfo entries
 	 for TLS.  */
@@ -64,7 +74,10 @@ do_test (int argc, char *argv[])
       xpthread_join (thr);
     }
 
-  free (path);
+  /* The elf subdirectory (or $ORIGIN in the container case) is on the
+     library search path.  */
+  check_dlopen_failure ("tst-dlopen-aout");
+
   return 0;
 }