linux-ext4 - Re: [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name

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Date:   Thu, 11 Jun 2020 11:01:50 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     Eric Biggers <ebiggers@...nel.org>, linux-ext4@...r.kernel.org,
        Daniel Rosenberg <drosen@...gle.com>, stable@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.co.uk>
Subject: Re: [PATCH v2] ext4: avoid utf8_strncasecmp() with unstable name

On Mon, Jun 01, 2020 at 02:49:51PM -0600, Andreas Dilger wrote:
> On Jun 1, 2020, at 2:05 PM, Eric Biggers <ebiggers@...nel.org> wrote:
> > 
> > From: Eric Biggers <ebiggers@...gle.com>
> > 
> > If the dentry name passed to ->d_compare() fits in dentry::d_iname, then
> > it may be concurrently modified by a rename.  This can cause undefined
> > behavior (possibly out-of-bounds memory accesses or crashes) in
> > utf8_strncasecmp(), since fs/unicode/ isn't written to handle strings
> > that may be concurrently modified.
> > 
> > Fix this by first copying the filename to a stack buffer if needed.
> > This way we get a stable snapshot of the filename.
> > 
> > Fixes: b886ee3e778e ("ext4: Support case-insensitive file name lookups")
> > Cc: <stable@...r.kernel.org> # v5.2+
> > Cc: Al Viro <viro@...iv.linux.org.uk>
> > Cc: Daniel Rosenberg <drosen@...gle.com>
> > Cc: Gabriel Krisman Bertazi <krisman@...labora.co.uk>
> > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> 
> LGTM.
> 
> Reviewed-by: Andreas Dilger <adilger@...ger.ca>

Thanks, applied.

					- Ted