dlopen: Rework handling of pending NODELETE status

Commit a2e8aa0d9ea648068d8be52dd7b15f1b6a008e23 ("Block signals during
the initial part of dlopen") was deemed necessary because of
read-modify-write operations like the one in  add_dependency in
elf/dl-lookup.c.  In the old code, we check for any kind of NODELETE
status and bail out:

      /* Redo the NODELETE check, as when dl_load_lock wasn't held
	 yet this could have changed.  */
      if (map->l_nodelete != link_map_nodelete_inactive)
	goto out;

And then set pending status (during relocation):

	  if (flags & DL_LOOKUP_FOR_RELOCATE)
	    map->l_nodelete = link_map_nodelete_pending;
	  else
	    map->l_nodelete = link_map_nodelete_active;

If a signal arrives during relocation and the signal handler, through
lazy binding, adds a global scope dependency on the same map, it will
set map->l_nodelete to link_map_nodelete_active.  This will be
overwritten with link_map_nodelete_pending by the dlopen relocation
code.

To avoid such problems in relation to the l_nodelete member, this
commit introduces two flags for active NODELETE status (irrevocable)
and pending NODELETE status (revocable until activate_nodelete is
invoked).  As a result, NODELETE processing in dlopen does not
introduce further reasons why lazy binding from signal handlers
is unsafe during dlopen, and a subsequent commit can remove signal
blocking from dlopen.

This does not address pre-existing issues (unrelated to the NODELETE
changes) which make lazy binding in a signal handler during dlopen
unsafe, such as the use of malloc in both cases.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index 075683d729..ea4e304bef 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -164,7 +164,7 @@ elf_get_dynamic_info (struct link_map *l, ElfW(Dyn) *temp)
     {
       l->l_flags_1 = info[VERSYMIDX (DT_FLAGS_1)]->d_un.d_val;
       if (l->l_flags_1 & DF_1_NODELETE)
-	l->l_nodelete = link_map_nodelete_pending;
+	l->l_nodelete_pending = true;
 
       /* Only DT_1_SUPPORTED_MASK bits are supported, and we would like
 	 to assert this, but we can't. Users have been setting