[pve-devel] [PATCH proxmox-backup-qemu 2/2] invalidate bitmap when crypto key changes

[Stefan Reiter]

On 10/21/20 1:49 PM, Fabian Grünbichler wrote:
> by computing and remembering the ID digest of a static string, we can
> detect when the passed in key has changed without keeping a copy of it
> around inbetween backup jobs.
> 
> this is a follow-up/fixup for
> 
> 104fae9111cd9a4e4dd7779172d39580a393165d fix #2866: invalidate bitmap on crypt_mode change
> 
> which implemented detection for crypt MODE changes.
> 
> Signed-off-by: Fabian Grünbichler <f.gruenbichler at proxmox.com>
> ---
> note: the string is just an implementation detail right now, but once we
> start sending that along with migration or persisting it together with
> bitmaps, we probably want a more robust scheme and store the input
> string + digest

I'm not sure I follow... as long as this string stays the same it 
shouldn't ever be necessary to store it alongside the digest?

In any case, this works fine:

Reviewed-by: Stefan Reiter <s.reiter at proxmox.com>

> 
>   src/backup.rs   |  1 +
>   src/commands.rs | 36 ++++++++++++++++++++++++++++++++++++
>   2 files changed, 37 insertions(+)
> 
> diff --git a/src/backup.rs b/src/backup.rs
> index 7945575..9f6d176 100644
> --- a/src/backup.rs
> +++ b/src/backup.rs
> @@ -203,6 +203,7 @@ impl BackupTask {
>               Some(ref manifest) => {
>                   check_last_incremental_csum(Arc::clone(manifest), &device_name, size)
>                       && check_last_encryption_mode(Arc::clone(manifest), &device_name, self.crypt_mode)
> +                    && check_last_encryption_key(self.crypt_config.clone())
>               },
>               None => false,
>           }
> diff --git a/src/commands.rs b/src/commands.rs
> index b9b0161..f7e0f62 100644
> --- a/src/commands.rs
> +++ b/src/commands.rs
> @@ -19,6 +19,10 @@ lazy_static!{
>       static ref PREVIOUS_CSUMS: Mutex<HashMap<String, [u8;32]>> = {
>           Mutex::new(HashMap::new())
>       };
> +
> +    static ref PREVIOUS_CRYPT_CONFIG_DIGEST: Mutex<Option<[u8;32]>> = {
> +        Mutex::new(None)
> +    };
>   }
>   
>   pub struct ImageUploadInfo {
> @@ -82,6 +86,15 @@ fn archive_name(device_name: &str) -> String {
>       format!("{}.img.fidx", device_name)
>   }
>   
> +const CRYPT_CONFIG_HASH_INPUT:&[u8] = b"this is just a static string to protect against key changes";
> +
> +/// Create an identifying digest for the crypt config
> +pub(crate) fn crypt_config_digest(
> +    config: Arc<CryptConfig>,
> +) -> [u8;32] {
> +    config.compute_digest(CRYPT_CONFIG_HASH_INPUT)
> +}
> +
>   pub(crate) fn check_last_incremental_csum(
>       manifest: Arc<BackupManifest>,
>       device_name: &str,
> @@ -114,6 +127,19 @@ pub(crate) fn check_last_encryption_mode(
>       }
>   }
>   
> +pub(crate) fn check_last_encryption_key(
> +    config: Option<Arc<CryptConfig>>,
> +) -> bool {
> +    let digest_guard = PREVIOUS_CRYPT_CONFIG_DIGEST.lock().unwrap();
> +    match (*digest_guard, config)  {
> +        (Some(last_digest), Some(current_config)) => {
> +            crypt_config_digest(current_config) == last_digest
> +        },
> +        (None, None) => true,
> +        _ => false,
> +    }
> +}
> +
>   #[allow(clippy::too_many_arguments)]
>   pub(crate) async fn register_image(
>       client: Arc<BackupWriter>,
> @@ -393,6 +419,16 @@ pub(crate) async fn finish_backup(
>               .map_err(|err| format_err!("unable to format manifest - {}", err))?
>       };
>   
> +    {
> +        let crypt_config_digest = match crypt_config {
> +            Some(current_config) => Some(crypt_config_digest(current_config)),
> +            None => None,
> +        };
> +
> +        let mut crypt_config_digest_guard = PREVIOUS_CRYPT_CONFIG_DIGEST.lock().unwrap();
> +        *crypt_config_digest_guard = crypt_config_digest;
> +    }
> +
>       client
>           .upload_blob_from_data(manifest.into_bytes(), MANIFEST_BLOB_NAME, true, false)
>           .await?;
>