linux-hardening - Re: [RFC] Get siginfo from unreaped task

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Date:   Sat, 12 Feb 2022 12:23:55 +0100
From:   Robert Święcki <robert@...ecki.net>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jann Horn <jannh@...gle.com>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [RFC] Get siginfo from unreaped task

sob., 12 lut 2022 o 05:28 Kees Cook <keescook@...omium.org> napisał(a):
>
> Make siginfo available through PTRACE_GETSIGINFO after process death,
> without needing to have already used PTRACE_ATTACH. Uses 48 more bytes
> in task_struct, though I bet there might be somewhere else we could
> stash a copy of it?

An alternative way of accessing this info could be abusing the
waitid() interface, with some additional, custom to Linux, flag

waitid(P_ALL, 0, &si, __WCHILDSIGINFO);

which would change what is put into si.

But maybe ptrace() is better, because it's mostly incompatible with
other OSes anyway on the behavior/flag level, while waitd() seems to
be POSIX/BSD standard, even if Linux specifies some additional flags.

-- 
Robert Święcki