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Rafael Aquini authored
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1999707
CVE: CVE-2021-3759

This patch is a backport of the following upstream commit:
commit 6a4746ba06191e23d30230738e94334b26590a8a
Author: Vasily Averin <vvs@virtuozzo.com>
Date:   Sat Sep 11 10:40:08 2021 +0300

    ipc: remove memcg accounting for sops objects in do_semtimedop()

    Linus proposes to revert an accounting for sops objects in
    do_semtimedop() because it's really just a temporary buffer
    for a single semtimedop() system call.

    This object can consume up to 2 pages, syscall is sleeping
    one, size and duration can be controlled by user, and this
    allocation can be repeated by many thread at the same time.

    However Shakeel Butt pointed that there are much more popular
    objects with the same life time and similar memory
    consumption, the accounting of which was decided to be
    rejected for performance reasons.

    Considering at least 2 pages for task_struct and 2 pages for
    the kernel stack, a back of the envelope calculation gives a
    footprint amplification of <1.5 so this temporal buffer can be
    safely ignored.

    The factor would IMO be interesting if it was >> 2 (from the
    PoV of excessive (ab)use, fine-grained accounting seems to be
    currently unfeasible due to performance impact).

    Link: https://lore.kernel.org/lkml/90e254df-0dfe-f080-011e-b7c53ee7fd20@virtuozzo.com/


    Fixes: 18319498fdd4 ("memcg: enable accounting of ipc resources")
Signed-off-by: default avatarVasily Averin <vvs@virtuozzo.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Reviewed-by: default avatarMichal Koutný <mkoutny@suse.com>
Acked-by: default avatarShakeel Butt <shakeelb@google.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: default avatarRafael Aquini <aquini@redhat.com>
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