linux-kernel - Re: [PATCH 14/20] exit/syscall_user_dispatch: Send ordinary signals on failure

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Message-ID: <875ytq1gkj.fsf@collabora.com>
Date:   Thu, 21 Oct 2021 13:35:40 -0300
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 14/20] exit/syscall_user_dispatch: Send ordinary signals
 on failure

"Eric W. Biederman" <ebiederm@...ssion.com> writes:

> Use force_fatal_sig instead of calling do_exit directly.  This ensures
> the ordinary signal handling path gets invoked, core dumps as
> appropriate get created, and for multi-threaded processes all of the
> threads are terminated not just a single thread.
>
> When asked Gabriel Krisman Bertazi <krisman@...labora.com> said [1]:
>> ebiederm@...ssion.com (Eric W. Biederman) asked:
>>
>> > Why does do_syscal_user_dispatch call do_exit(SIGSEGV) and
>> > do_exit(SIGSYS) instead of force_sig(SIGSEGV) and force_sig(SIGSYS)?
>> >
>> > Looking at the code these cases are not expected to happen, so I would
>> > be surprised if userspace depends on any particular behaviour on the
>> > failure path so I think we can change this.
>>
>> Hi Eric,
>>
>> There is not really a good reason, and the use case that originated the
>> feature doesn't rely on it.
>>
>> Unless I'm missing yet another problem and others correct me, I think
>> it makes sense to change it as you described.
>>
>> > Is using do_exit in this way something you copied from seccomp?
>>
>> I'm not sure, its been a while, but I think it might be just that.  The
>> first prototype of SUD was implemented as a seccomp mode.
>
> If at some point it becomes interesting we could relax
> "force_fatal_sig(SIGSEGV)" to instead say
> "force_sig_fault(SIGSEGV, SEGV_MAPERR, sd->selector)".
>
> I avoid doing that in this patch to avoid making it possible
> to catch currently uncatchable signals.
>
> Cc: Gabriel Krisman Bertazi <krisman@...labora.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> [1] https://lkml.kernel.org/r/87mtr6gdvi.fsf@collabora.com
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>  kernel/entry/syscall_user_dispatch.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>

Hi Eric,

Feel free to add:

Reviewed-by: Gabriel Krisman Bertazi <krisman@...labora.com>

Thanks,

-- 
Gabriel Krisman Bertazi