be_sync: avoid crashing on files in the root of a DB

If a sync DB is malformed and contains entries in the root of the
archive, load_pkg_for_entry will leave the 'filename' variable empty,
leading to a crash in the ensuing strcmp() calls which determine the DB
fragment being examined.

While this isn't a read error, this should be reported to the user so
that it can be addressed by the creator of the DB.

As seen: https://bbs.archlinux.org/viewtopic.php?pid=1297766

Signed-off-by: Dave Reisner <dreisner@archlinux.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/libalpm/be_sync.c b/lib/libalpm/be_sync.c
index bd68739f..0b996843 100644
--- a/lib/libalpm/be_sync.c
+++ b/lib/libalpm/be_sync.c
@@ -562,6 +562,14 @@ static int sync_db_read(alpm_db_t *db, struct archive *archive,
 		return -1;
 	}
 
+	if(filename == NULL) {
+		/* A file exists outside of a subdirectory. This isn't a read error, so return
+		 * success and try to continue on. */
+		_alpm_log(db->handle, ALPM_LOG_WARNING, _("unknown database file: %s\n"),
+				filename);
+		return 0;
+	}
+
 	if(strcmp(filename, "desc") == 0 || strcmp(filename, "depends") == 0
 			|| (strcmp(filename, "deltas") == 0 && db->handle->deltaratio > 0.0) ) {
 		int ret;