linux-kernel - Re: [PATCH 1/9] kernel: add a PF_FORCE

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Message-ID: <20200920181208.GO3421308@ZenIV.linux.org.uk>
Date:   Sun, 20 Sep 2020 19:12:08 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Linux SCSI List <linux-scsi@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        linux-aio <linux-aio@...ck.org>, io-uring@...r.kernel.org,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Network Development <netdev@...r.kernel.org>,
        keyrings@...r.kernel.org,
        LSM List <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag

On Sun, Sep 20, 2020 at 09:59:36AM -0700, Andy Lutomirski wrote:

> As one example, look at __sys_setsockopt().  It's called for the
> native and compat versions, and it contains an in_compat_syscall()
> check.  (This particularly check looks dubious to me, but that's
> another story.)  If this were to be done with equivalent semantics
> without a separate COMPAT_DEFINE_SYSCALL and without
> in_compat_syscall(), there would need to be some indication as to
> whether this is compat or native setsockopt.  There are other
> setsockopt implementations in the net stack with more
> legitimate-seeming uses of in_compat_syscall() that would need some
> other mechanism if in_compat_syscall() were to go away.
> 
> setsockopt is (I hope!) out of scope for io_uring, but the situation
> isn't fundamentally different from read and write.

	Except that setsockopt() had that crap very widespread; for read()
and write() those are very rare exceptions.

	Andy, please RTFS.  Or dig through archives.  The situation
with setsockopt() is *NOT* a good thing - it's (probably) the least
of the evils.  The last thing we need is making that the norm.