linux-kernel - Re: [PATCH V6 01/10] Use copy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <68ba89ae-108e-c14a-02a0-db72b169c9b1@oracle.com>
Date:   Tue, 18 Jan 2022 12:51:27 -0600
From:   Mike Christie <michael.christie@...cle.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     geert@...ux-m68k.org, vverma@...italocean.com, hdanton@...a.com,
        hch@...radead.org, stefanha@...hat.com, jasowang@...hat.com,
        mst@...hat.com, sgarzare@...hat.com,
        virtualization@...ts.linux-foundation.org,
        christian.brauner@...ntu.com, axboe@...nel.dk,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 01/10] Use copy_process in vhost layer

On 1/17/22 11:31 AM, Eric W. Biederman wrote:
> Mike Christie <michael.christie@...cle.com> writes:
> 
>> On 12/22/21 12:24 PM, Eric W. Biederman wrote:
>>> All I am certain of is that you need to set
>>> "args->exit_signal = -1;".  This prevents having to play games with
>>> do_notify_parent.
>>
>> Hi Eric,
>>
>> I have all your review comments handled except this one. It's looking like it's
>> more difficult than just setting the exit_signal=-1, so I wanted to check that
>> I understood you.
> 
> [snip problems with exit_signal = -1]
> 
>>
>> What do you think?
> 
> I was wrong.  I appear to have confused the thread and the non-thread
> cases.
> 
> Perhaps I meant "args->exit_signal = 0".  That looks like
> do_notify_parent won't send it, and thread_group_leader continues to do
> the right thing.

That doesn't work too. exit_notify will call do_notify_parent but 
our parent, qemu, does not ignore SIGCHILD so we will not drop
down in into this chunk:

        psig = tsk->parent->sighand;
        spin_lock_irqsave(&psig->siglock, flags);
        if (!tsk->ptrace && sig == SIGCHLD &&
            (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN ||
             (psig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT))) {

do_notify_parent will return false and so autoreap in exit_notify will
be false.



> 
> Baring any additional confusion on my part that cleanly solves the
> problem of how not to send a signal from a child process cleanly.
> 
> My apologies for sending you on a wild goose chase.
> 

It's no problem. I learned a lot about signal handling :)