rafs: add special handling of invalid zero blob index

The rafs v6 format reserves blob index 0 for meta blobs, so ensure
invalid zero blob index doesn't cause abnormal behavior.

Signed-off-by: Jiang Liu <gerry@linux.alibaba.com>

rafs/src/metadata/direct_v6.rs

@@ -537,8 +537,17 @@ impl OndiskInodeWrapper {
         is_tarfs_mode: bool,
         is_tail: bool,
     ) -> Option<BlobIoDesc> {
-        let blob_index = chunk_addr.blob_index();
         let chunk_index = chunk_addr.blob_ci_index();
+        let blob_index = match chunk_addr.blob_index() {
+            Err(e) => {
+                warn!(
+                    "failed to get blob index for chunk address {:?}, {}",
+                    chunk_addr, e
+                );
+                return None;
+            }
+            Ok(v) => v,
+        };
 
         match state.blob_table.get(blob_index) {
             Err(e) => {
@@ -1310,7 +1319,7 @@ impl RafsInodeExt for OndiskInodeWrapper {
         let has_device = self.mapping.device.lock().unwrap().has_device();
 
         if state.meta.has_inlined_chunk_digest() && has_device {
-            let blob_index = chunk_addr.blob_index();
+            let blob_index = chunk_addr.blob_index()?;
             let chunk_index = chunk_addr.blob_ci_index();
             let device = self.mapping.device.lock().unwrap();
             device
@@ -1322,7 +1331,7 @@ impl RafsInodeExt for OndiskInodeWrapper {
                     ))
                 })
         } else if state.is_tarfs() {
-            let blob_index = chunk_addr.blob_index();
+            let blob_index = chunk_addr.blob_index()?;
             let chunk_index = chunk_addr.blob_ci_index();
             let offset = (chunk_addr.block_addr() as u64) << EROFS_BLOCK_BITS_9;
             let size = if idx == self.get_chunk_count() - 1 {
@@ -1340,7 +1349,7 @@ impl RafsInodeExt for OndiskInodeWrapper {
             match chunk_map.as_ref().unwrap().get(chunk_addr) {
                 None => Err(enoent!(format!(
                     "failed to get chunk info for chunk {}/{}/{}",
-                    chunk_addr.blob_index(),
+                    chunk_addr.blob_index().unwrap_or_default(),
                     chunk_addr.blob_ci_index(),
                     chunk_addr.block_addr()
                 ))),

rafs/src/metadata/layout/v6.rs

@@ -1196,8 +1196,13 @@ impl RafsV6InodeChunkAddr {
     /// The index in BlobInfo grows from 0, so when using this method to index the corresponding blob,
     /// the index always needs to be minus 1
     /// Get the blob index of the chunk.
-    pub fn blob_index(&self) -> u32 {
-        (u16::from_le(self.c_blob_addr_hi) & 0x00ff) as u32 - 1
+    pub fn blob_index(&self) -> Result<u32> {
+        let idx = (u16::from_le(self.c_blob_addr_hi) & 0x00ff) as u32;
+        if idx == 0 {
+            Err(einval!("invalid zero blob index from RafsV6InodeChunkAddr"))
+        } else {
+            Ok(idx - 1)
+        }
     }
 
     /// Set the blob index of the chunk.
@@ -2356,4 +2361,20 @@ mod tests {
             assert!(entry2 == target1);
         }
     }
+
+    #[test]
+    fn test_invalid_blob_idx_from_chunk_addr() {
+        let mut addr = RafsV6InodeChunkAddr::new();
+        assert!(addr.blob_index().is_err());
+        addr.set_blob_index(8);
+        assert_eq!(addr.blob_index(), 8);
+
+        assert_eq!(addr.blob_ci_index(), 0);
+        addr.set_blob_ci_index(131);
+        assert_eq!(addr.blob_ci_index(), 131);
+
+        assert_eq!(addr.block_addr(), 0);
+        addr.set_block_addr(179);
+        assert_eq!(addr.block_addr(), 179);
+    }
 }