[pbs-devel] [PATCH proxmox-backup] pxar: client: fix missing file size check for metadata comparison

[Christian Ebner]

Change detection mode set to metadata compares regular file entries
metadata to the reference metadata archive of the previous run. The
`pxar::format::Stat` as stored in `pxar::Metadata` however does not
include the actual file size, it only partially stores information
gathered from stating the file.

This means however that the actual file size is never compared and
therefore, that if the file size did change, but the other metadata
information did not (including the mtime which might have been
restored), that file will be incorrectly reused.
A subsequent restore will however fail, because the expected file size
as encoded in the metadata archive does not match the file size as
stored in the payload archive.

Fix this by adding the missing file size check, comparing the size
for the given file against the one stored in the metadata archive.

Link to issue reported in community forum:
https://forum.proxmox.com/threads/158722/

Signed-off-by: Christian Ebner <c.ebner at proxmox.com>
---
 pbs-client/src/pxar/create.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/pbs-client/src/pxar/create.rs b/pbs-client/src/pxar/create.rs
index c7d274b8c..33a4c29e6 100644
--- a/pbs-client/src/pxar/create.rs
+++ b/pbs-client/src/pxar/create.rs
@@ -423,6 +423,7 @@ impl Archiver {
         previous_metadata_accessor: &Option<Directory<MetadataArchiveReader>>,
         file_name: &Path,
         metadata: &Metadata,
+        file_size: u64,
     ) -> Result<Option<Range<u64>>, Error> {
         if let Some(previous_metadata_accessor) = previous_metadata_accessor {
             if let Some(file_entry) = previous_metadata_accessor.lookup(file_name).await? {
@@ -433,6 +434,9 @@ impl Archiver {
                         ..
                     } = file_entry.entry().kind()
                     {
+                        if file_size != *size {
+                            return Ok(None);
+                        }
                         let range =
                             *offset..*offset + size + size_of::<pxar::format::Header>() as u64;
                         debug!(
@@ -798,8 +802,9 @@ impl Archiver {
             }
 
             let file_name: &Path = OsStr::from_bytes(c_file_name.to_bytes()).as_ref();
+            let file_size = stat.st_size as u64;
             if let Some(payload_range) = self
-                .is_reusable_entry(previous_metadata, file_name, &metadata)
+                .is_reusable_entry(previous_metadata, file_name, &metadata, file_size)
                 .await?
             {
                 if !self.cache.try_extend_range(payload_range.clone()) {
-- 
2.39.5