[Bug nptl/12889] Race condition in pthread_kill

["cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=12889

--- Comment #10 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Florian Weimer <fw@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2849e2f53311b66853cb5159b64cba2bddbfb854

commit 2849e2f53311b66853cb5159b64cba2bddbfb854
Author: Florian Weimer <fweimer@redhat.com>
Date:   Thu Sep 23 09:55:54 2021 +0200

    nptl: Avoid setxid deadlock with blocked signals in thread exit [BZ #28361]

    As part of the fix for bug 12889, signals are blocked during
    thread exit, so that application code cannot run on the thread that
    is about to exit.  This would cause problems if the application
    expected signals to be delivered after the signal handler revealed
    the thread to still exist, despite pthread_kill can no longer be used
    to send signals to it.  However, glibc internally uses the SIGSETXID
    signal in a way that is incompatible with signal blocking, due to the
    way the setxid handshake delays thread exit until the setxid operation
    has completed.  With a blocked SIGSETXID, the handshake can never
    complete, causing a deadlock.

    As a band-aid, restore the previous handshake protocol by not blocking
    SIGSETXID during thread exit.

    The new test sysdeps/pthread/tst-pthread-setuid-loop.c is based on
    a downstream test by Martin Osvald.

    Reviewed-by: Carlos O'Donell <carlos@redhat.com>
    Tested-by: Carlos O'Donell <carlos@redhat.com>

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