patch "staging: erofs: avoid endless loop of invalid lookback distance 0" added to staging-testing

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    staging: erofs: avoid endless loop of invalid lookback distance 0

to my staging git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-testing branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will be merged to the staging-next branch sometime soon,
after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.


From 07ae24a38ac0254a5d955e4646806b756a426c0c Mon Sep 17 00:00:00 2001
From: Gao Xiang <gaoxiang25@huawei.com>
Date: Mon, 19 Aug 2019 18:34:26 +0800
Subject: 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.

Fixes: 02827e1796b3 ("staging: erofs: add erofs_map_blocks_iter")
Cc: <stable@vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Link: https://lore.kernel.org/r/20190819103426.87579-7-gaoxiang25@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/staging/erofs/zmap.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/staging/erofs/zmap.c b/drivers/staging/erofs/zmap.c
index 7408e86823a4..774dacbc5b32 100644
--- a/drivers/staging/erofs/zmap.c
+++ b/drivers/staging/erofs/zmap.c
@@ -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;
-- 
2.23.0