linux-kernel - Re: [RFC][PATCH 1/5] exit: kill struct waitid

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Message-ID: <20190725094051.GC4707@redhat.com>
Date:   Thu, 25 Jul 2019 11:40:52 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian@...uner.io>
Cc:     linux-kernel@...r.kernel.org, arnd@...db.de, ebiederm@...ssion.com,
        keescook@...omium.org, joel@...lfernandes.org, tglx@...utronix.de,
        tj@...nel.org, dhowells@...hat.com, jannh@...gle.com,
        luto@...nel.org, akpm@...ux-foundation.org, cyphar@...har.com,
        torvalds@...ux-foundation.org, viro@...iv.linux.org.uk,
        kernel-team@...roid.com
Subject: Re: [RFC][PATCH 1/5] exit: kill struct waitid_info

On 07/24, Christian Brauner wrote:
>
> Note that this changes how struct siginfo is filled in for users of
> waitid.

Namely, copy_siginfo_to_user() will nullify the extra SI_EXPANSION_SIZE
bytes + 2*sizeof(__ARCH_SI_CLOCK_T) from _sigchld (waitid doesn't report
utime/stime in siginfo).

Looks correct... even the compat case, but please double-check
copy_siginfo_to_user32/siginfo_layout. Looks like both SIL_KILL and
SIL_CHLD cases are fine in that this patch can't add other user-visible
changes, but I could easily miss something.

> In case
> anyone relies on the old behavior we can just revert

we won't need to rever the whole patch, we can just replace
copy_siginfo_to_user() with copy_to_user(offsetof(si_utime)).

I see you are going to update the changelog and resend, feel free to add
my reviewed-by.

Oleg.