linux-kernel - Re: [PATCH RESEND] exec: don't force_sigsegv processes with a pending fatal signal

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Message-ID: <20180803133923.GA19752@redhat.com>
Date:   Fri, 3 Aug 2018 15:39:24 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Dmitry Safonov <0x7f454c46@...il.com>
Cc:     Ivan Delalande <colona@...sta.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH RESEND] exec: don't force_sigsegv processes with a
 pending fatal signal

On 08/02, Dmitry Safonov wrote:
>
> Hi Ivan,
>
> 2018-07-31 1:56 GMT+01:00 Ivan Delalande <colona@...sta.com>:
> > We were seeing unexplained segfaults in coreutils processes and other
> > basic utilities that we tracked down to binfmt_elf failing to load
> > segments for ld.so. Digging further, the actual problem seems to occur
> > when a process gets sigkilled while it is still being loaded by the
> > kernel. In our case when _do_page_fault goes for a retry it will return
> > early as it first checks for fatal_signal_pending(), so load_elf_interp
> > also returns with error and as a result search_binary_handler will
> > force_sigsegv() which is pretty confusing as nothing actually failed
> > here.
> >
> > Fixes: 19d860a140be ("handle suicide on late failure exits in execve() in search_binary_handler()")
> > Reference: https://lkml.org/lkml/2013/2/14/5
> > Signed-off-by: Ivan Delalande <colona@...sta.com>
>
> +Cc: Oleg Nesterov <oleg@...hat.com>
> +Cc: Andy Lutomirski <luto@...nel.org>

Thanks...

and sorry, I fail to understand the problem and what/how this patch tries to fix.

Hmm. After I read the next email from Dmitry it seems to me that the whole purpose
of this patch is to avoid print_fatal_signal()? If yes, the changelog should clearly
explain this.

> > --- a/fs/exec.c
> > +++ b/fs/exec.c
> > @@ -1656,7 +1656,8 @@ int search_binary_handler(struct linux_binprm *bprm)
> >                 if (retval < 0 && !bprm->mm) {
> >                         /* we got to flush_old_exec() and failed after it */
> >                         read_unlock(&binfmt_lock);
> > -                       force_sigsegv(SIGSEGV, current);
> > +                       if (!fatal_signal_pending(current))
> > +                               force_sigsegv(SIGSEGV, current);

I won't argue, but may be force_sigsegv() should check fatal_signal_pending()
itself. setup_rt_frame() can too fail if fatal_signal_pending() by the same
reason.

Oleg.