Re: [Qemu-devel] [PATCH v5 3/4] crypto.c: cleanup created file when block_crypto_co_create_opts_luks fails

[John Snow]

On 8/7/19 10:21 AM, Daniel Henrique Barboza wrote:
> When using a non-UTF8 secret to create a volume using qemu-img, the
> following error happens:
> 
> $ qemu-img create -f luks --object 
> secret,id=vol_1_encrypt0,file=vol_resize_pool.vol_1.secret.qzVQrI -o 
> key-secret=vol_1_encrypt0 /var/tmp/pool_target/vol_1 10240K
> 
> Formatting '/var/tmp/pool_target/vol_1', fmt=luks size=10485760 
> key-secret=vol_1_encrypt0
> qemu-img: /var/tmp/pool_target/vol_1: Data from secret vol_1_encrypt0 is not 
> valid UTF-8
> 
> However, the created file '/var/tmp/pool_target/vol_1' is left behind in the
> file system after the failure. This behavior can be observed when creating
> the volume using Libvirt, via 'virsh vol-create', and then getting "volume
> target path already exist" errors when trying to re-create the volume.
> 
> The volume file is created inside block_crypto_co_create_opts_luks(), in
> block/crypto.c. If the bdrv_create_file() call is successful but any
> succeeding step fails*, the existing 'fail' label does not take into
> account the created file, leaving it behind.
> 
> This patch changes block_crypto_co_create_opts_luks() to delete
> 'filename' in case of failure. A failure in this point means that
> the volume is now truncated/corrupted, so even if 'filename' was an
> existing volume before calling qemu-img, it is now unusable. Deleting
> the file it is not much worse than leaving it in the filesystem in
> this scenario, and we don't have to deal with checking the file
> pre-existence in the code.
> 
> * in our case, block_crypto_co_create_generic calls qcrypto_block_create,
> which calls qcrypto_block_luks_create, and this function fails when
> calling qcrypto_secret_lookup_as_utf8.
> 
> Reported-by: Srikanth Aithal <address@hidden>
> Suggested-by: Kevin Wolf <address@hidden>
> Signed-off-by: Daniel Henrique Barboza <address@hidden>
> ---
>  block/crypto.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/block/crypto.c b/block/crypto.c
> index 8237424ae6..8ffca81df6 100644
> --- a/block/crypto.c
> +++ b/block/crypto.c
> @@ -30,6 +30,7 @@
>  #include "qapi/error.h"
>  #include "qemu/module.h"
>  #include "qemu/option.h"
> +#include "qemu/cutils.h"
>  #include "crypto.h"
>  
>  typedef struct BlockCrypto BlockCrypto;
> @@ -575,6 +576,25 @@ fail:
>      bdrv_unref(bs);
>      qapi_free_QCryptoBlockCreateOptions(create_opts);
>      qobject_unref(cryptoopts);
> +
> +    /*
> +     * If an error occurred, delete the file. Even if the file existed
> +     * beforehand, it has been truncated and corrupted in the process.
> +     */
> +    if (ret) {
> +        Error *local_err;
> +        int r_del = bdrv_delete_file(filename, &local_err);
> +        /*
> +         * ENOTSUP will happen if the block driver doesn't support
> +         * 'bdrv_co_delete_file'. ENOENT will happen if the file
> +         * doesn't exist. Both are predictable and shouldn't be
> +         * reported back to the user.
> +         */

Hm, actually, didn't you use ENOENT to mean that we couldn't figure out
which driver to use?

> +        if ((r_del < 0) && (r_del != -ENOTSUP) && (r_del != -ENOENT)) {
> +            error_reportf_err(local_err, "%s: ", bs->filename);
> +        }> +    }
> +
>      return ret;
>  }
>  
>