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

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

[fweimer at redhat dot com]

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

            Bug ID: 30785
           Summary: Always call destructors in reverse constructor order
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
  Target Milestone: ---

Since

commit 1df71d32fe5f5905ffd5d100e5e9ca8ad6210891
Author: Florian Weimer <fweimer@redhat.com>
Date:   Tue Sep 20 11:00:42 2022 +0200

    elf: Implement force_first handling in _dl_sort_maps_dfs (bug 28937)

    The implementation in _dl_close_worker requires that the first
    element of l_initfini is always this very map (“We are always the
    zeroth entry, and since we don't include ourselves in the
    dependency analysis start at 1.”).  Rather than fixing that
    assumption, this commit adds an implementation of the force_first
    argument to the new dependency sorting algorithm.  This also means
    that the directly dlopen'ed shared object is always initialized last,
    which is the least surprising behavior in the presence of cycles.

    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

it is very likely that with cyclic dependencies, the destructor ordering is not
the reverse of the constructor ordering because there is no working force_first
handling for _dl_fini/dlclose. Reportedly, this results in application
problems.

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

[fweimer at redhat dot com]

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

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fweimer at redhat dot com
              Flags|                            |security-
           See Also|                            |https://bugzilla.redhat.com
                   |                            |/show_bug.cgi?id=2233338

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

[fweimer at redhat dot com]

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

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=28937

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

[fweimer at redhat dot com]

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

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at sourceware dot org   |fweimer at redhat dot com

--- Comment #1 from Florian Weimer <fweimer at redhat dot com> ---
Patch posted:

[PATCH v3 0/2] Predictable ELF destructor ordering (bug 30785)
<https://inbox.sourceware.org/libc-alpha/cover.1692701787.git.fweimer@redhat.com/>

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

[sam at gentoo dot org]

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

Sam James <sam at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sam at gentoo dot org

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

[fweimer at redhat dot com]

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

[sam at gentoo dot org]

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

Sam James <sam at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=15903

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

[sam at gentoo dot org]

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

Sam James <sam at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |2.39

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

[fweimer at redhat dot com]

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

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=30869

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

[fweimer at redhat dot com]

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

Florian Weimer <fweimer at redhat dot com> changed:

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

--- Comment #3 from Florian Weimer <fweimer at redhat dot com> ---
I think this change needs to be reverted.

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

[fweimer at redhat dot com]

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

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|2.39                        |---

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

[fweimer at redhat dot com]

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

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|REOPENED                    |RESOLVED

--- Comment #4 from Florian Weimer <fweimer at redhat dot com> ---
The change has been reverted on all branches due to unforeseen application
compatibility issues.

I will file a new bug for a concrete issue in dlclose that I identified
regarding destructor ordering. We can work on a targeted fix for that.

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

[fweimer at redhat dot com]

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

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://sourceware.org/bugz
                   |                            |illa/show_bug.cgi?id=30981

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

[fweimer at redhat dot com]

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

--- Comment #5 from Florian Weimer <fweimer at redhat dot com> ---
Bug 30981 is the continuation issue for dlclose.

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