Add additional safety check against invalid backup label file

It was already checking for invalid data after "BACKUP FROM", but
would possibly crash if "BACKUP FROM" was missing altogether.

found by Coverity

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 18fc23286aa30fa2534b6d0fa56365a6f790195e..ff7f521a1b1bb33b010221c0deef1a7ec8591266 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -9481,7 +9481,7 @@ do_pg_stop_backup(char *labelfile, bool waitforarchive)
     * during the backup.
     */
    ptr = strstr(remaining, "BACKUP FROM:");
-   if (sscanf(ptr, "BACKUP FROM: %19s\n", backupfrom) != 1)
+   if (!ptr || sscanf(ptr, "BACKUP FROM: %19s\n", backupfrom) != 1)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                 errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));