Re: [Qemu-devel] [PATCH 10/13] block/crypto: implement the encryption key management

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

On Wed, Aug 14, 2019 at 11:22:16PM +0300, Maxim Levitsky wrote:
> This implements the encryption key management
> using the generic code in qcrypto layer
> 
> This code adds another 'write_func' because the initialization
> write_func works directly on the underlying file,
> because during the creation, there is no open instance
> of the luks driver, but during regular use, we have it,
> and should use it instead.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  block/crypto.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 93 insertions(+), 3 deletions(-)
> 
> diff --git a/block/crypto.c b/block/crypto.c
> index 42a3f0898b..415b6db041 100644
> --- a/block/crypto.c
> +++ b/block/crypto.c
> @@ -36,6 +36,7 @@ typedef struct BlockCrypto BlockCrypto;
>  
>  struct BlockCrypto {
>      QCryptoBlock *block;
> +    bool updating_keys;
>  };
>  
>  
> @@ -69,6 +70,24 @@ static ssize_t block_crypto_read_func(QCryptoBlock *block,
>      return ret;
>  }
>  
> +static ssize_t block_crypto_write_func(QCryptoBlock *block,
> +                                      size_t offset,
> +                                      const uint8_t *buf,
> +                                      size_t buflen,
> +                                      void *opaque,
> +                                      Error **errp)
> +{
> +    BlockDriverState *bs = opaque;
> +    ssize_t ret;
> +
> +    ret = bdrv_pwrite(bs->file, offset, buf, buflen);
> +    if (ret < 0) {
> +        error_setg_errno(errp, -ret, "Could not write encryption header");
> +        return ret;
> +    }
> +    return ret;
> +}
> +
>  
>  struct BlockCryptoCreateData {
>      BlockBackend *blk;
> @@ -622,6 +641,78 @@ block_crypto_get_specific_info_luks(BlockDriverState *bs, Error **errp)
>      return spec_info;
>  }
>  
> +
> +static int
> +block_crypto_setup_encryption(BlockDriverState *bs,
> +                              enum BlkSetupEncryptionAction action,
> +                              QCryptoEncryptionSetupOptions *options,
> +                              bool force,
> +                              Error **errp)
> +{
> +    BlockCrypto *crypto = bs->opaque;
> +    int ret;
> +
> +    assert(crypto);
> +    assert(crypto->block);
> +
> +    crypto->updating_keys = true;
> +
> +    ret = bdrv_child_refresh_perms(bs, bs->file, errp);
> +
> +    if (ret) {
> +        crypto->updating_keys = false;
> +        return ret;
> +    }
> +
> +    ret = qcrypto_block_setup_encryption(crypto->block,
> +                                          block_crypto_read_func,
> +                                          block_crypto_write_func,
> +                                          bs,
> +                                          action,
> +                                          options,
> +                                          force,
> +                                          errp);
> +
> +    crypto->updating_keys = false;
> +    bdrv_child_refresh_perms(bs, bs->file, errp);
> +
> +
> +    return ret;
> +
> +}
> +
> +
> +static void
> +block_crypto_child_perms(BlockDriverState *bs, BdrvChild *c,
> +                         const BdrvChildRole *role,
> +                         BlockReopenQueue *reopen_queue,
> +                         uint64_t perm, uint64_t shared,
> +                         uint64_t *nperm, uint64_t *nshared)
> +{
> +
> +    BlockCrypto *crypto = bs->opaque;
> +
> +    /*
> +     * This driver doesn't modify LUKS metadata except
> +     * when updating the encryption slots.
> +     * Allow share-rw=on as a special case.
> +     *
> +     * Encryption update will set the crypto->updating_keys
> +     * during that period and refresh permissions
> +     *
> +     * */
> +
> +    if (crypto->updating_keys) {
> +        /*need exclusive write access for header update  */
> +        perm |= BLK_PERM_WRITE;
> +        shared &= ~BLK_PERM_WRITE;
> +    }

So if 2 QEMU's have the same LUKS image open, this means that
if one tries to update the header, it will fail to upgrade
its lock & thus be blocked from updating header ?

> +
> +    bdrv_filter_default_perms(bs, c, role, reopen_queue,
> +            perm, shared, nperm, nshared);
> +}

Regards,
Daniel
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