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, 42 insertions, 7 deletions

diff --git a/elf/dl-object.c b/elf/dl-object.c
index c3f5455..e952058 100644
--- a/elf/dl-object.c
+++ b/elf/dl-object.c
@@ -57,14 +57,30 @@ struct link_map *
 _dl_new_object (char *realname, const char *libname, int type,
 		struct link_map *loader, int mode, Lmid_t nsid)
 {
+#ifdef SHARED
+  unsigned int naudit;
+  if (__glibc_unlikely ((mode & __RTLD_OPENEXEC) != 0))
+    {
+      assert (type == lt_executable);
+      assert (nsid == LM_ID_BASE);
+
+      /* Ignore the specified libname for the main executable.  It is
+	 only known with an explicit loader invocation.  */
+      libname = "";
+
+      /* We create the map for the executable before we know whether
+	 we have auditing libraries and if yes, how many.  Assume the
+	 worst.  */
+      naudit = DL_NNS;
+    }
+  else
+    naudit = GLRO (dl_naudit);
+#endif
+
   size_t libname_len = strlen (libname) + 1;
   struct link_map *new;
   struct libname_list *newname;
 #ifdef SHARED
-  /* We create the map for the executable before we know whether we have
-     auditing libraries and if yes, how many.  Assume the worst.  */
-  unsigned int naudit = GLRO(dl_naudit) ?: ((mode & __RTLD_OPENEXEC)
-					    ? DL_NNS : 0);
   size_t audit_space = naudit * sizeof (new->l_audit[0]);
 #else
 # define audit_space 0
@@ -91,8 +107,20 @@ _dl_new_object (char *realname, const char *libname, int type,
      and won't get dumped during core file generation. Therefore to assist
      gdb and to create more self-contained core files we adjust l_name to
      point at the newly allocated copy (which will get dumped) instead of
-     the ld.so rodata copy.  */
-  new->l_name = *realname ? realname : (char *) newname->name + libname_len - 1;
+     the ld.so rodata copy.
+
+     Furthermore, in case of explicit loader invocation, discard the
+     name of the main executable, to match the regular behavior, where
+     name of the executable is not known.  */
+#ifdef SHARED
+  if (*realname != '\0' && (mode & __RTLD_OPENEXEC) == 0)
+#else
+  if (*realname != '\0')
+#endif
+    new->l_name = realname;
+  else
+    new->l_name = (char *) newname->name + libname_len - 1;
+
   new->l_type = type;
   /* If we set the bit now since we know it is never used we avoid
      dirtying the cache line later.  */
@@ -149,7 +177,14 @@ _dl_new_object (char *realname, const char *libname, int type,
 
   new->l_local_scope[0] = &new->l_searchlist;
 
-  /* Don't try to find the origin for the main map which has the name "".  */
+  /* Determine the origin.  If allocating the link map for the main
+     executable, the realname is not known and "".  In this case, the
+     origin needs to be determined by other means.  However, in case
+     of an explicit loader invocation, the pathname of the main
+     executable is known and needs to be processed here: From the
+     point of view of the kernel, the main executable is the
+     dynamic loader, and this would lead to a computation of the wrong
+     origin.  */
   if (realname[0] != '\0')
     {
       size_t realname_len = strlen (realname) + 1;