From 6985865bc3ad5b23147ee73466583dd7fdf65892 Mon Sep 17 00:00:00 2001 From: Florian Weimer Date: Fri, 8 Sep 2023 12:32:14 +0200 Subject: elf: Always call destructors in reverse constructor order (bug 30785) The current implementation of dlclose (and process exit) re-sorts the link maps before calling ELF destructors. Destructor order is not the reverse of the constructor order as a result: The second sort takes relocation dependencies into account, and other differences can result from ambiguous inputs, such as cycles. (The force_first handling in _dl_sort_maps is not effective for dlclose.) After the changes in this commit, there is still a required difference due to dlopen/dlclose ordering by the application, but the previous discrepancies went beyond that. A new global (namespace-spanning) list of link maps, _dl_init_called_list, is updated right before ELF constructors are called from _dl_init. In dl_close_worker, the maps variable, an on-stack variable length array, is eliminated. (VLAs are problematic, and dlclose should not call malloc because it cannot readily deal with malloc failure.) Marking still-used objects uses the namespace list directly, with next and next_idx replacing the done_index variable. After marking, _dl_init_called_list is used to call the destructors of now-unused maps in reverse destructor order. These destructors can call dlopen. Previously, new objects do not have l_map_used set. This had to change: There is no copy of the link map list anymore, so processing would cover newly opened (and unmarked) mappings, unloading them. Now, _dl_init (indirectly) sets l_map_used, too. (dlclose is handled by the existing reentrancy guard.) After _dl_init_called_list traversal, two more loops follow. The processing order changes to the original link map order in the namespace. Previously, dependency order was used. The difference should not matter because relocation dependencies could already reorder link maps in the old code. The changes to _dl_fini remove the sorting step and replace it with a traversal of _dl_init_called_list. The l_direct_opencount decrement outside the loader lock is removed because it appears incorrect: the counter manipulation could race with other dynamic loader operations. tst-audit23 needs adjustments to the changes in LA_ACT_DELETE notifications. The new approach for checking la_activity should make it clearer that la_activty calls come in pairs around namespace updates. The dependency sorting test cases need updates because the destructor order is always the opposite order of constructor order, even with relocation dependencies or cycles present. There is a future cleanup opportunity to remove the now-constant force_first and for_fini arguments from the _dl_sort_maps function. Fixes commit 1df71d32fe5f5905ffd5d100e5e9ca8ad62 ("elf: Implement force_first handling in _dl_sort_maps_dfs (bug 28937)"). Reviewed-by: DJ Delorie --- include/link.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include') diff --git a/include/link.h b/include/link.h index 1d74feb2bd..69bda3ed17 100644 --- a/include/link.h +++ b/include/link.h @@ -278,6 +278,10 @@ struct link_map /* List of object in order of the init and fini calls. */ struct link_map **l_initfini; + /* Linked list of objects in reverse ELF constructor execution + order. Head of list is stored in _dl_init_called_list. */ + struct link_map *l_init_called_next; + /* List of the dependencies introduced through symbol binding. */ struct link_map_reldeps { -- cgit 1.4.1