[PATCH proxmox-backup 20/20] sync: pull: decrypt snapshots with matching encryption key fingerprint

[Christian Ebner <c.ebner@proxmox.com>]

Decrypt any backup snapshot during pull which was encrypted with a
matching encryption key. Matching of keys is performed by comparing
the fingerprint of the key as stored in the source manifest and the
key configured for the pull sync jobs.

If matching, pass along the key's crypto config to the index and chunk
readers and write the local files unencrypted instead of simply
downloading them. A new manifest file is written instead of the
original one and files registered accordingly.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 src/server/pull.rs | 78 ++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 76 insertions(+), 2 deletions(-)

diff --git a/src/server/pull.rs b/src/server/pull.rs
index 05152d0dd..22b058056 100644
--- a/src/server/pull.rs
+++ b/src/server/pull.rs
@@ -3,6 +3,7 @@
 use std::collections::hash_map::Entry;
 use std::collections::{HashMap, HashSet};
 use std::io::{BufReader, Read, Seek, Write};
+use std::os::fd::AsRawFd;
 use std::sync::atomic::{AtomicU64, AtomicUsize, Ordering};
 use std::sync::{Arc, Mutex};
 use std::time::SystemTime;
@@ -10,11 +11,14 @@ use std::time::SystemTime;
 use anyhow::{bail, format_err, Context, Error};
 use pbs_tools::crypt_config::CryptConfig;
 use proxmox_human_byte::HumanByte;
+use serde_json::Value;
+use tokio::fs::OpenOptions;
+use tokio::io::AsyncWriteExt;
 use tracing::{info, warn};
 
 use pbs_api_types::{
     print_store_and_ns, ArchiveType, Authid, BackupArchiveName, BackupDir, BackupGroup,
-    BackupNamespace, GroupFilter, Operation, RateLimitConfig, Remote, SnapshotListItem,
+    BackupNamespace, CryptMode, GroupFilter, Operation, RateLimitConfig, Remote, SnapshotListItem,
     VerifyState, CLIENT_LOG_BLOB_NAME, MANIFEST_BLOB_NAME, MAX_NAMESPACE_DEPTH,
     PRIV_DATASTORE_AUDIT, PRIV_DATASTORE_BACKUP,
 };
@@ -397,6 +401,7 @@ async fn pull_single_archive<'a>(
     encountered_chunks: Arc<Mutex<EncounteredChunks>>,
     crypt_config: Option<Arc<CryptConfig>>,
     backend: &DatastoreBackend,
+    new_manifest: Option<Arc<Mutex<BackupManifest>>>,
 ) -> Result<SyncStats, Error> {
     let archive_name = &archive_info.filename;
     let mut path = snapshot.full_path();
@@ -446,6 +451,17 @@ async fn pull_single_archive<'a>(
 
                     // Overwrite current tmp file so it will be persisted instead
                     std::fs::rename(&path, &tmp_path)?;
+
+                    if let Some(new_manifest) = new_manifest {
+                        let name = archive_name.as_str().try_into()?;
+                        // size is indetical to original, encrypted index
+                        new_manifest.lock().unwrap().add_file(
+                            &name,
+                            size,
+                            csum,
+                            CryptMode::None,
+                        )?;
+                    }
                 }
 
                 sync_stats.add(stats);
@@ -484,6 +500,17 @@ async fn pull_single_archive<'a>(
 
                     // Overwrite current tmp file so it will be persisted instead
                     std::fs::rename(&path, &tmp_path)?;
+
+                    if let Some(new_manifest) = new_manifest {
+                        let name = archive_name.as_str().try_into()?;
+                        // size is indetical to original, encrypted index
+                        new_manifest.lock().unwrap().add_file(
+                            &name,
+                            size,
+                            csum,
+                            CryptMode::None,
+                        )?;
+                    }
                 }
 
                 sync_stats.add(stats);
@@ -522,6 +549,14 @@ async fn pull_single_archive<'a>(
                     decrypted_tmpfile.rewind()?;
                     let (csum, size) = sha256(&mut decrypted_tmpfile)?;
 
+                    if let Some(new_manifest) = new_manifest {
+                        let mut new_manifest = new_manifest.lock().unwrap();
+                        let name = archive_name.as_str().try_into()?;
+                        new_manifest.add_file(&name, size, csum, CryptMode::None)?;
+                    }
+
+                    nix::unistd::fsync(decrypted_tmpfile.as_raw_fd())?;
+
                     std::fs::rename(&decrypted_tmp_path, &tmp_path)?;
 
                     Ok::<(), Error>(())
@@ -607,9 +642,11 @@ async fn pull_snapshot<'a>(
             let _ = std::fs::remove_file(&tmp_manifest_name);
             return Ok(sync_stats); // nothing changed
         }
+        // redownload also in case of encrypted, even if key would match as cannot
+        // fully verify otherwise due to file checksum mismatches.
     }
 
-    let manifest_data = tmp_manifest_blob.raw_data().to_vec();
+    let mut manifest_data = tmp_manifest_blob.raw_data().to_vec();
     let manifest = BackupManifest::try_from(tmp_manifest_blob)?;
 
     if ignore_not_verified_or_encrypted(
@@ -629,6 +666,16 @@ async fn pull_snapshot<'a>(
     }
 
     let mut crypt_config = None;
+    let mut new_manifest = None;
+    if let Ok(Some(source_fingerprint)) = manifest.fingerprint() {
+        if let Some(config) = &params.crypt_config {
+            if config.fingerprint() == *source_fingerprint.bytes() {
+                crypt_config = Some(Arc::clone(config));
+                new_manifest = Some(Arc::new(Mutex::new(BackupManifest::new(snapshot.into()))));
+                info!("Found matching key fingerprint {source_fingerprint}, decrypt on pull");
+            }
+        }
+    }
 
     let backend = &params.target.backend;
     for item in manifest.files() {
@@ -678,11 +725,38 @@ async fn pull_snapshot<'a>(
             encountered_chunks.clone(),
             crypt_config.clone(),
             backend,
+            new_manifest.clone(),
         )
         .await?;
         sync_stats.add(stats);
     }
 
+    if let Some(new_manifest) = new_manifest {
+        let mut new_manifest = Arc::try_unwrap(new_manifest)
+            .map_err(|_arc| {
+                format_err!("failed to take ownership of still referenced new manifest")
+            })?
+            .into_inner()
+            .unwrap();
+
+        // copy over notes ecc, but drop encryption key fingerprint
+        new_manifest.unprotected = manifest.unprotected.clone();
+        new_manifest.unprotected["key-fingerprint"] = Value::Null;
+
+        let manifest_string = new_manifest.to_string(None)?;
+        let manifest_blob = DataBlob::encode(manifest_string.as_bytes(), None, true)?;
+        // update contents to be uploaded to backend
+        manifest_data = manifest_blob.raw_data().to_vec();
+
+        let mut tmp_manifest_file = OpenOptions::new()
+            .write(true)
+            .truncate(true) // clear pre-existing manifest content
+            .open(&tmp_manifest_name)
+            .await?;
+        tmp_manifest_file.write_all(&manifest_data).await?;
+        tmp_manifest_file.flush().await?;
+    }
+
     if let Err(err) = std::fs::rename(&tmp_manifest_name, &manifest_name) {
         bail!("Atomic rename file {:?} failed - {}", manifest_name, err);
     }
-- 
2.47.3