File dlopen-filter-object.patch of Package glibc.15121
From eb447b7b4bd6177f876ba9420ad9e048c27bae91 Mon Sep 17 00:00:00 2001
From: David Kilroy <David.Kilroy@arm.com>
Date: Wed, 12 Feb 2020 14:28:15 -0300
Subject: [PATCH] elf: Allow dlopen of filter object to work [BZ #16272]
There are two fixes that are needed to be able to dlopen filter
objects. First _dl_map_object_deps cannot assume that map will be at
the beginning of l_searchlist.r_list[], as filtees are inserted before
map. Secondly dl_open_worker needs to ensure that filtees get
relocated.
In _dl_map_object_deps:
* avoiding removing relocation dependencies of map by setting
l_reserved to 0 and otherwise processing the rest of the search
list.
* ensure that map remains at the beginning of l_initfini - the list
of things that need initialisation (and destruction). Do this by
splitting the copy up. This may not be required, but matches the
initialization order without dlopen.
Modify dl_open_worker to relocate the objects in new->l_inifini.
new->l_initfini is constructed in _dl_map_object_deps, and lists the
objects that need initialization and destruction. Originally the list
of objects in new->l_next are relocated. All of these objects should
also be included in new->l_initfini (both lists are populated with
dependencies in _dl_map_object_deps). We can't use new->l_prev to pick
up filtees, as during a recursive dlopen from an interposed malloc
call, l->prev can contain objects that are not ready for relocation.
Add tests to verify that symbols resolve to the filtee implementation
when auxiliary and filter objects are used, both as a normal link and
when dlopen'd.
Tested by running the testsuite on x86_64.
Index: glibc-2.26/elf/dl-deps.c
===================================================================
--- glibc-2.26.orig/elf/dl-deps.c
+++ glibc-2.26/elf/dl-deps.c
@@ -506,14 +506,18 @@ _dl_map_object_deps (struct link_map *ma
map->l_searchlist.r_list = &l_initfini[nlist + 1];
map->l_searchlist.r_nlist = nlist;
+ unsigned int map_index = UINT_MAX;
for (nlist = 0, runp = known; runp; runp = runp->next)
{
if (__builtin_expect (trace_mode, 0) && runp->map->l_faked)
/* This can happen when we trace the loading. */
--map->l_searchlist.r_nlist;
- else
+ else {
+ if (runp->map == map)
+ map_index = nlist;
map->l_searchlist.r_list[nlist++] = runp->map;
+ }
/* Now clear all the mark bits we set in the objects on the search list
to avoid duplicates, so the next call starts fresh. */
@@ -571,13 +575,14 @@ Filters not supported with LD_TRACE_PREL
}
/* Maybe we can remove some relocation dependencies now. */
- assert (map->l_searchlist.r_list[0] == map);
struct link_map_reldeps *l_reldeps = NULL;
if (map->l_reldeps != NULL)
{
- for (i = 1; i < nlist; ++i)
+ for (i = 0; i < nlist; ++i)
map->l_searchlist.r_list[i]->l_reserved = 1;
+ /* Avoid removing relocation dependencies of the main binary. */
+ map->l_reserved = 0;
struct link_map **list = &map->l_reldeps->list[0];
for (i = 0; i < map->l_reldeps->act; ++i)
if (list[i]->l_reserved)
@@ -602,16 +607,30 @@ Filters not supported with LD_TRACE_PREL
}
}
- for (i = 1; i < nlist; ++i)
+ for (i = 0; i < nlist; ++i)
map->l_searchlist.r_list[i]->l_reserved = 0;
}
- /* Sort the initializer list to take dependencies into account. The binary
- itself will always be initialize last. */
- memcpy (l_initfini, map->l_searchlist.r_list,
- nlist * sizeof (struct link_map *));
- /* We can skip looking for the binary itself which is at the front of
- the search list. */
+ /* Sort the initializer list to take dependencies into account. Always
+ initialize the binary itself last. */
+ assert (map_index < nlist);
+ if (map_index > 0)
+ {
+ /* Copy the binary into position 0. */
+ l_initfini[0] = map->l_searchlist.r_list[map_index];
+
+ /* Copy the filtees. */
+ for (i = 0; i < map_index; ++i)
+ l_initfini[i+1] = map->l_searchlist.r_list[i];
+
+ /* Copy the remainder. */
+ for (i = map_index + 1; i < nlist; ++i)
+ l_initfini[i] = map->l_searchlist.r_list[i];
+ }
+ else
+ memcpy (l_initfini, map->l_searchlist.r_list,
+ nlist * sizeof (struct link_map *));
+
_dl_sort_maps (&l_initfini[1], nlist - 1, NULL, false);
/* Terminate the list of dependencies. */
Index: glibc-2.26/elf/dl-open.c
===================================================================
--- glibc-2.26.orig/elf/dl-open.c
+++ glibc-2.26/elf/dl-open.c
@@ -314,22 +314,25 @@ dl_open_worker (void *a)
allows IFUNC relocations to work and it also means copy
relocation of dependencies are if necessary overwritten. */
unsigned int nmaps = 0;
- struct link_map *l = new;
+ unsigned int j = 0;
+ struct link_map *l = new->l_initfini[0];
do
{
if (! l->l_real->l_relocated)
++nmaps;
- l = l->l_next;
+ l = new->l_initfini[++j];
}
while (l != NULL);
+ /* Stack allocation is limited by the number of loaded objects. */
struct link_map *maps[nmaps];
nmaps = 0;
- l = new;
+ j = 0;
+ l = new->l_initfini[0];
do
{
if (! l->l_real->l_relocated)
maps[nmaps++] = l;
- l = l->l_next;
+ l = new->l_initfini[++j];
}
while (l != NULL);
_dl_sort_maps (maps, nmaps, NULL, false);