linux-kernel - Re: [PATCH v2 1/6] fs/readdir: Fix filldir() and filldir64() use of user_access

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Message-ID: <CAHk-=whCk8z2_kggSCoAGMne8PNSvcT2T4bBH62ngoFrsTyV6w@mail.gmail.com>
Date:   Thu, 23 Jan 2020 10:38:29 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/6] fs/readdir: Fix filldir() and filldir64() use of user_access_begin()

On Thu, Jan 23, 2020 at 4:00 AM Michael Ellerman <mpe@...erman.id.au> wrote:
>
> So I guess I'll wait and see what happens with patch 1.

I've committed my fixes to filldir[64]() directly - they really were
fixing me being lazy about the range, and the name length checking
really is a theoretical "access wrong user space pointer" issue with
corrupted filesystems regardless (even though I suspect it's entirely
theoretical - even a corrupt filesystem hopefully won't be passing in
negative directory entry lengths or something like that).

The "pass in read/write" part I'm not entirely convinced about.
Honestly, if this is just for ppc32 and nobody else really needs it,
make the ppc32s thing always just enable both user space reads and
writes. That's the semantics for x86 and arm as is, I'm not convinced
that we should complicate this for a legacy platform.

                Linus