linux-kernel - Re: oopsably broken case-insensitive support in ext4 and f2fs (Re: vfat: Broken case-insensitive support for UTF-8)

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Date:   Thu, 23 Jan 2020 20:29:53 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Pali Rohár <pali.rohar@...il.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Namjae Jeon <linkinjeon@...il.com>,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: oopsably broken case-insensitive support in ext4 and f2fs (Re:
 vfat: Broken case-insensitive support for UTF-8)

On Mon, Jan 20, 2020 at 07:35:58PM +0000, Al Viro wrote:
> On Mon, Jan 20, 2020 at 08:07:21AM +0000, Al Viro wrote:
> 
> > > > I hadn't checked ->d_compare() instances for a while; somebody needs to
> > > > do that again, by the look of it.  The above definitely is broken;
> > > > no idea how many other instaces had grown such bugs...
> > > 
> > > f2fs one also has the same bug.  Anyway, I'm going down right now, will
> > > check the rest tomorrow morning...
> > 
> > We _probably_ can get away with just checking that inode for NULL and
> > buggering off if it is (->d_seq mismatch is guaranteed in that case),
> > but I suspect that we might need READ_ONCE() on both dereferences.
> > I hate memory barriers...
> 
> FWIW, other instances seem to be OK; HFS+ one might or might not be
> OK in the face of concurrent rename (wrong result in that case is
> no problem; oops would be), but it doesn't play silly buggers with
> pointer-chasing.
> 
> ext4 and f2fs do, and ->d_compare() is broken in both of them.

Thanks Al.  I sent out fixes for this:

ext4: https://lore.kernel.org/r/20200124041234.159740-1-ebiggers@kernel.org
f2fs: https://lore.kernel.org/r/20200124041549.159983-1-ebiggers@kernel.org

Note that ->d_hash() was broken too.  In fact, that was much easier to
reproduce.

- Eric