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

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Date:   Tue, 9 Jun 2020 13:28:21 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Daniel Rosenberg <drosen@...gle.com>, stable@...r.kernel.org,
        linux-ext4@...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 01:05:43PM -0700, Eric Biggers 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>
> ---
> 
> v2: use memcpy() + barrier() instead of a byte-by-byte copy.
> 
>  fs/ext4/dir.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)

Ted, could you take this through the ext4 tree as a fix for 5.8?
The f2fs patch has been merged already.

- Eric