linux-kernel - Re: [PATCH v2 00/20] Fix handling of compat_siginfo

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Date:	Mon, 9 Nov 2015 16:12:04 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"Amanieu d'Antras" <amanieu@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
	linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	sparclinux@...r.kernel.org,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Kenton Varda <kenton@...dstorm.io>
Subject: Re: [PATCH v2 00/20] Fix handling of compat_siginfo_t

On 11/07, Andy Lutomirski wrote:
>
> On Wed, Nov 4, 2015 at 4:50 PM, Amanieu d'Antras <amanieu@...il.com> wrote:
> > One issue that isn't resolved in this series is sending signals between a 32-bit
> > process and 64-bit process. Sending a si_int will work correctly, but a si_ptr
> > value will likely get corrupted due to the different layouts of the 32-bit and
> > 64-bit siginfo_t structures.
>
> This is so screwed up it's not even funny.

Agreed,

> A 64-bit big-endian compat calls rt_sigqueueinfo.  It passes in (among
> other things) a sigval_t.  The kernel can choose to interpret it

I always thought that the kernel should not interpret it at all. And indeed,
copy_siginfo_to_user() does

	if (from->si_code < 0)
		return __copy_to_user(to, from, sizeof(siginfo_t))

probably copy_siginfo_to_user32() should do something similar, at least
it should not truncate ->si_code it it is less than zero.

Not sure what signalfd_copyinfo() should do.

But perhaps I was wrong, I failed to find man sigqueueinfo, and man
sigqueue() documents that it passes sigval_t.


> BTW, x86 has its own set of screwups here.  Somehow cr2 and error_code
> ended up as part of ucontext instead of siginfo, which makes
> absolutely no sense to me and bloats task_struct.

Yes, and probably ->ip should have been the part of siginfo too. Say,
if you get SIGBUS you can't trust sc->ip if another signal was dequeued
before SIGBUS, in this case sc->ip will point to the handler of that
another signal. That is why we have SYNCHRONOUS_MASK and it helps, but
still this doesn't look nice.

Oleg.

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