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

Eric Biggers
2020-06-09T20:28:27Z

On Mon, Jun 01, 2020 at 01:05:43PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.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@vger.kernel.org> # v5.2+
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Daniel Rosenberg <drosen@google.com>
> Cc: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
> Signed-off-by: Eric Biggers <ebiggers@google.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