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elf: Include libc.so.6 as main program in dependency sort (bug 20972)

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_dl_map_object_deps always sorts the initially loaded object first
during dependency sorting.  This means it is relocated last in
dl_open_worker.  This results in crashes in IFUNC resolvers without
lazy bindings if libraries are preloaded that refer to IFUNCs in
libc.so.6: the resolvers are called when libc.so.6 has not been
relocated yet, so references to _rtld_global_ro etc. crash.

The fix is to check against the libc.so.6 link map recorded by the
__libc_early_init framework, and let it participate in the dependency
sort.

This fixes bug 20972.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Florian Weimer
2020-12-11 17:30:03 +01:00
parent cb81264fd9
commit 9ffa50b26b
3 changed files with 43 additions and 2 deletions
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7
elf/dl-deps.c
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@ -611,7 +611,12 @@ Filters not supported with LD_TRACE_PRELINKING"));
memcpy (l_initfini, map->l_searchlist.r_list,
nlist * sizeof (struct link_map *));
_dl_sort_maps (&l_initfini[1], nlist - 1, NULL, false);
/* If libc.so.6 is the main map, it participates in the sort, so
that the relocation order is correct regarding libc.so.6. */
if (l_initfini[0] == GL (dl_ns)[l_initfini[0]->l_ns].libc_map)
_dl_sort_maps (l_initfini, nlist, NULL, false);
else
_dl_sort_maps (&l_initfini[1], nlist - 1, NULL, false);
/* Terminate the list of dependencies. */
l_initfini[nlist] = NULL;