Re: [PATCH] fscrypt: restrict IV_INO_LBLK_32 to ino_bits <= 32

[Eric Biggers <ebiggers@kernel.org>]

On Mon, Aug 24, 2020 at 01:38:41PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
> 
> When an encryption policy has the IV_INO_LBLK_32 flag set, the IV
> generation method involves hashing the inode number.  This is different
> from fscrypt's other IV generation methods, where the inode number is
> either not used at all or is included directly in the IVs.
> 
> Therefore, in principle IV_INO_LBLK_32 can work with any length inode
> number.  However, currently fscrypt gets the inode number from
> inode::i_ino, which is 'unsigned long'.  So currently the implementation
> limit is actually 32 bits (like IV_INO_LBLK_64), since longer inode
> numbers will have been truncated by the VFS on 32-bit platforms.
> 
> Fix fscrypt_supported_v2_policy() to enforce the correct limit.
> 
> This doesn't actually matter currently, since only ext4 and f2fs support
> IV_INO_LBLK_32, and they both only support 32-bit inode numbers.  But we
> might as well fix it in case it matters in the future.
> 
> Ideally inode::i_ino would instead be made 64-bit, but for now it's not
> needed.  (Note, this limit does *not* prevent filesystems with 64-bit
> inode numbers from adding fscrypt support, since IV_INO_LBLK_* support
> is optional and is useful only on certain hardware.)
> 
> Fixes: e3b1078bedd3 ("fscrypt: add support for IV_INO_LBLK_32 policies")
> Reported-by: Jeff Layton <jlayton@kernel.org>
> Signed-off-by: Eric Biggers <ebiggers@google.com>

Applied to fscrypt.git#master for 5.10.

- Eric