[Bug dynamic-link/30785] Always call destructors in reverse constructor order

["fweimer at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30785

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Florian Weimer <fweimer at redhat dot com> ---
Fixed in 2.39 via:

commit 6985865bc3ad5b23147ee73466583dd7fdf65892
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Sep 8 12:32:14 2023 +0200

    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 <dj@redhat.com>

Backports in progress.

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