DT_RUNPATH of executable not found when loader and dl_caller is libasan.so

Navin P navinp0304@gmail.com
Mon Feb 22 09:35:45 GMT 2021

 My scenario is    $HOME/package/ contains ./a.out and dso libplugin.so.
  Without address sanitizer(asan) libasan.so mode using gcc , if i run
./a.out from $HOME/package i'm able to find libplugin.so and it prints
dlopen succeeded.
Now if i go to the parent directy and cd ..  . If i run
./package/a.out , it is able to find and prints dlopen succeeded .
Everything is good until here.
libplugin.so is an empty shared object without asan..


int main(){
        void *handle=dlopen("libplugin.so",RTLD_NOW);
                printf("dlopen succeeded\n");
        } else {
                printf("dlopen failed\n");
        return 0;

Now i compile the example and .so with -fsanitize=address. Now in the
case of running a.out from  $HOME/package , it prints dlopen
Now if i do cd.. and run ./package/a.out from $HOME it fails and
prints dlopen failed. This is because the loader is changed to
libasan.so and this
time the DT_RUNPATH is checked for RUNPATH of libasan. This works for
RPATH because we check for all the list of loaders and we find the
base loader whose rpath is $HOME/package. But in case of DT_RUNPATH we
don't .
I think an additional lookup needs to be performed after the old
RUNPATH code in dl-load.c which looks up for
GL(dl_ns)[LM_ID_BASE]._ns_loaded when fd==-1.

I've tested this patch and it works fine for me.

>From d2cb9bba3de58af3516eb7099d0452e2ee6365d2 Mon Sep 17 00:00:00 2001
From: Navin P <navinp0304@gmail.com>
Date: Mon, 22 Feb 2021 15:02:00 +0530
Subject: [PATCH] If executables are compiled with asan, it should perform
 additional LM_ID_BASE D_RUNPATH also.

 elf/dl-load.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 9e2089cfaa..fe88c8c9ea 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -2161,6 +2161,34 @@ _dl_map_object (struct link_map *loader, const
char *name,
  &loader->l_runpath_dirs, &realname, &fb, loader,
  LA_SER_RUNPATH, &found_other_class);

+      /*
+       * This is not transitive dependency.It it just an additional
+       * lookup into executable/dso runpath when loader is different
+       * from LM_ID_BASE loader.
+       * In usual cases like direct call to executable, then main_map
+       * is same as loader and no lookup is performed.
+       * In cases like libasan.so being the parent caller with dl_caller
+       * set to libasan.so which is called by GL(dls_ns)[LIM_ID_BASE],
+       * we need to additionally search the executable/dso link_map
+       * other than loader link_map which is performed above.
+       */
+      struct link_map *main_map = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
+      /* Look at the RUNPATH information for this binary using main_map.
+       * This lookup is only done when the binary is in namespace 0.
+       * For nested namespaces from dlmopen LM_ID_NEWLM, we don't search
+       * in namespace 0 because it is detached from LM_ID_BASE.
+       * In that case lookup is done in the callers RUNPATH above.
+       */
+      if (fd == -1 && (nsid == LM_ID_BASE ) && main_map != NULL
+          && main_map != loader
+   && cache_rpath (main_map, &main_map->l_runpath_dirs,
+ fd = open_path (name, namelen, mode,
+ &main_map->l_runpath_dirs, &realname, &fb, main_map,
+ LA_SER_RUNPATH, &found_other_class);
       if (fd == -1)
           realname = _dl_sysdep_open_object (name, namelen, &fd);

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