Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200903142242.925828-1-hch@lst.de> <20200903142242.925828-6-hch@lst.de>
 <20201001223852.GA855@sol.localdomain> <20201001224051.GI3421308@ZenIV.linux.org.uk>
 <CAHk-=wgj=mKeN-EfV5tKwJNeHPLG0dybq+R5ZyGuc4WeUnqcmA@mail.gmail.com>
 <20201009220633.GA1122@sol.localdomain> <CAHk-=whcEzYjkqdpZciHh+iAdUttvfWZYoiHiF67XuTXB1YJLw@mail.gmail.com>
 <20201010011919.GC1122@sol.localdomain>
In-Reply-To: <20201010011919.GC1122@sol.localdomain>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 9 Oct 2020 18:29:13 -0700
Message-ID: <CAHk-=wigvcmp-jcgoNCbx45W7j3=0jA320CfpskwuoEjefM7nQ@mail.gmail.com>
Subject: Re: [PATCH 05/14] fs: don't allow kernel reads and writes without
 iter ops
To:     Eric Biggers <ebiggers@kernel.org>,
        Alexander Viro <aviro@redhat.com>
Cc:     Al Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@lst.de>,
        Michael Ellerman <mpe@ellerman.id.au>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Oct 9, 2020 at 6:19 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> Okay, that makes more sense.  So the patchset from Matthew
> https://lkml.kernel.org/linux-fsdevel/20201003025534.21045-1-willy@infradead.org/T/#u
> isn't what you had in mind.

No.

That first patch makes sense - it's just the "ppos can be NULL" patch.

But as mentioned, NULL isn't "shorthand for zero". It's just "pipes
don't _have_ a pos, trying to pass in some explicit position is
crazy".

So no, the other patches in that set are a bit odd, I think.

SOME of them look potentially fine - the bpfilter one seems to be
valid, for example, because it's literally about reading/writing a
pipe. And maybe the sysctl one is similarly sensible - I didn't check
the context of that one.

But no, NULL shouldn't mean "start at position zero, and we don't care
about the result".

              Linus