When reading GNU-style sparse archive entries, handle

the first sparse block correctly (we used to assume
that the first sparse block was always at offset zero).

1 files changed, 18 insertions, 8 deletions

diff --git a/lib/libarchive/archive_read_support_format_tar.c b/lib/libarchive/archive_read_support_format_tar.c
index e854c70..21ae3d3 100644
--- a/lib/libarchive/archive_read_support_format_tar.c
+++ b/lib/libarchive/archive_read_support_format_tar.c
@@ -450,24 +450,34 @@ archive_read_format_tar_read_data(struct archive *a,
 	struct sparse_block *p;
 
 	tar = *(a->pformat_data);
-	if (tar->entry_bytes_remaining > 0) {
-		bytes_read = (a->compression_read_ahead)(a, buff, 1);
-		if (bytes_read <= 0)
-			return (ARCHIVE_FATAL);
-		if (bytes_read > tar->entry_bytes_remaining)
-			bytes_read = tar->entry_bytes_remaining;
+	if (tar->sparse_list != NULL) {
+		/* Remove exhausted entries from sparse list. */
 		while (tar->sparse_list != NULL &&
 		    tar->sparse_list->remaining == 0) {
 			p = tar->sparse_list;
 			tar->sparse_list = p->next;
 			free(p);
-			if (tar->sparse_list != NULL)
-				tar->entry_offset = tar->sparse_list->offset;
 		}
+		if (tar->sparse_list == NULL) {
+			/* We exhausted the entire sparse list. */
+			tar->entry_bytes_remaining = 0;
+		}
+	}
+
+	if (tar->entry_bytes_remaining > 0) {
+		bytes_read = (a->compression_read_ahead)(a, buff, 1);
+		if (bytes_read <= 0)
+			return (ARCHIVE_FATAL);
+		if (bytes_read > tar->entry_bytes_remaining)
+			bytes_read = tar->entry_bytes_remaining;
 		if (tar->sparse_list != NULL) {
+			/* Don't read more than is available in the
+			 * current sparse block. */
 			if (tar->sparse_list->remaining < bytes_read)
 				bytes_read = tar->sparse_list->remaining;
+			tar->entry_offset = tar->sparse_list->offset;
 			tar->sparse_list->remaining -= bytes_read;
+			tar->sparse_list->offset += bytes_read;
 		}
 		*size = bytes_read;
 		*offset = tar->entry_offset;