Re: [Qemu-devel] [PATCH v4 13/18] qcow2: add support for LUKS encryption format

["Daniel P. Berrange" <berrange@redhat.com>]

On Thu, Feb 16, 2017 at 02:42:04PM +0100, Alberto Garcia wrote:
> On Fri 10 Feb 2017 06:09:05 PM CET, Daniel P. Berrange wrote:
> > @@ -990,12 +1123,6 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
> >      s->refcount_max = UINT64_C(1) << (s->refcount_bits - 1);
> >      s->refcount_max += s->refcount_max - 1;
> >  
> > -    if (header.crypt_method > QCOW_CRYPT_AES) {
> > -        error_setg(errp, "Unsupported encryption method: %" PRIu32,
> > -                   header.crypt_method);
> > -        ret = -EINVAL;
> > -        goto fail;
> > -    }
> 
> Here you remove the check for a valid encryption method...
> 
> >      s->crypt_method_header = header.crypt_method;
> >      if (s->crypt_method_header) {
> >          if (bdrv_uses_whitelist() &&
> > @@ -1012,6 +1139,12 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
> >              goto fail;
> >          }
> >  
> > +        if (s->crypt_method_header == QCOW_CRYPT_AES) {
> > +            s->crypt_physical_offset = false;
> > +        } else {
> > +            s->crypt_physical_offset = true;
> > +        }
> > +
> 
> ...and here you assume that if it's not AES then it must be LUKS.
> However at this point crypt_method_header hasn't been verified yet and
> can have any value.
> 
> The image will fail to open anyway because of the qcow2_update_options()
> call later in this function, but I think it wouldn't hurt to have an
> explicit check here, or at least an explanatory comment.

Yes, we're assuming LUKS and any future scheme we implement will
use the else{} code path, the first path is insecure.

> 
> > +static int qcow2_crypt_method_from_format(const char *format)
> > +{
> > +    if (g_str_equal(format, "luks")) {
> > +        return QCOW_CRYPT_LUKS;
> > +    } else if (g_str_equal(format, "aes")) {
> > +        return QCOW_CRYPT_AES;
> > +    } else {
> > +        return -EINVAL;
> > +    }
> > +}
> >  
> >  static int qcow2_set_up_encryption(BlockDriverState *bs, QemuOpts *opts,
> > -                                   Error **errp)
> > +                                   const char *format, Error **errp)
> >  {
> >      BDRVQcow2State *s = bs->opaque;
> >      QCryptoBlockCreateOptions *cryptoopts = NULL;
> >      QCryptoBlock *crypto = NULL;
> >      int ret = -EINVAL;
> >  
> > -    cryptoopts = block_crypto_create_opts_init(
> > -        Q_CRYPTO_BLOCK_FORMAT_QCOW, opts, "aes-", errp);
> > +    if (g_str_equal(format, "luks")) {
> > +        cryptoopts = block_crypto_create_opts_init(
> > +            Q_CRYPTO_BLOCK_FORMAT_LUKS, opts, "luks-", errp);
> > +        s->crypt_method_header = QCOW_CRYPT_LUKS;
> > +    } else if (g_str_equal(format, "aes")) {
> > +        cryptoopts = block_crypto_create_opts_init(
> > +            Q_CRYPTO_BLOCK_FORMAT_QCOW, opts, "aes-", errp);
> > +        s->crypt_method_header = QCOW_CRYPT_AES;
> > +    } else {
> 
> You just added a nice qcow2_crypt_method_from_format() function
> immediately before this one, I think this one would be more readable if
> you use it here.

Yes, it lets us turn it into a nicer switch()


Regards,
Daniel
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