Re: [PATCH] f2fs: don't use casefolded comparison for "." and ".."

[Gabriel Krisman Bertazi <krisman@collabora.com>]

Eric Biggers <ebiggers@kernel.org> writes:

> From: Eric Biggers <ebiggers@google.com>
>
> Tryng to rename a directory that has all following properties fails with
> EINVAL and triggers the 'WARN_ON_ONCE(!fscrypt_has_encryption_key(dir))'
> in f2fs_match_ci_name():
>
>     - The directory is casefolded
>     - The directory is encrypted
>     - The directory's encryption key is not yet set up
>     - The parent directory is *not* encrypted
>
> The problem is incorrect handling of the lookup of ".." to get the
> parent reference to update.  fscrypt_setup_filename() treats ".." (and
> ".") specially, as it's never encrypted.  It's passed through as-is, and
> setting up the directory's key is not attempted.  As the name isn't a
> no-key name, f2fs treats it as a "normal" name and attempts a casefolded
> comparison.  That breaks the assumption of the WARN_ON_ONCE() in
> f2fs_match_ci_name() which assumes that for encrypted directories,
> casefolded comparisons only happen when the directory's key is set up.
>
> We could just remove this WARN_ON_ONCE().  However, since casefolding is
> always a no-op on "." and ".." anyway, let's instead just not casefold
> these names.  This results in the standard bytewise comparison.
>
> Fixes: 7ad08a58bf67 ("f2fs: Handle casefolding with Encryption")
> Cc: <stable@vger.kernel.org> # v5.11+
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  fs/f2fs/dir.c  |  3 ++-
>  fs/f2fs/f2fs.h | 10 +++++-----
>  fs/f2fs/hash.c | 11 ++++++-----
>  3 files changed, 13 insertions(+), 11 deletions(-)

Hi Eric,

This looks good to me:

Reviewed-by: Gabriel Krisman Bertazi <krisman@collabora.com>

Thanks,

-- 
Gabriel Krisman Bertazi