FAILED: patch "[PATCH] staging: erofs: avoid endless loop of invalid lookback" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 598bb8913d015150b7734b55443c0e53e7189fc7 Mon Sep 17 00:00:00 2001
From: Gao Xiang <[email protected]>
Date: Mon, 19 Aug 2019 18:34:26 +0800
Subject: [PATCH] staging: erofs: avoid endless loop of invalid lookback
distance 0

As reported by erofs-utils fuzzer, Lookback distance should be a positive number, so it should be actually looked back rather than spinning.

index 7408e86823a4..774dacbc5b32 100644
@@ -350,6 +350,12 @@ static int vle_extent_lookback(struct z_erofs_maprecorder *m,
 
 	switch (m->type) {
 	case Z_EROFS_VLE_CLUSTER_TYPE_NONHEAD:
+		if (unlikely(!m->delta[0])) {
+			errln("invalid lookback distance 0 at nid %llu",
+			      vi->nid);
+			DBG_BUGON(1);
+			return -EFSCORRUPTED;
+		}
 		return vle_extent_lookback(m, m->delta[0]);
 	case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
 		map->m_flags &= ~EROFS_MAP_ZIPPED;