[PATCH 6/6] staging: erofs: avoid endless loop of invalid lookback distance 0

From: Gao Xiang <gaoxiang25@huawei.com>
To: Chao Yu <yuchao0@huawei.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	<devel@driverdev.osuosl.org>, <linux-fsdevel@vger.kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	<linux-erofs@lists.ozlabs.org>, "Chao Yu" <chao@kernel.org>,
	Miao Xie <miaoxie@huawei.com>, <weidu.du@huawei.com>,
	Fang Wei <fangwei1@huawei.com>, Gao Xiang <gaoxiang25@huawei.com>,
	<stable@vger.kernel.org>
Subject: [PATCH 6/6] staging: erofs: avoid endless loop of invalid lookback distance 0
Date: Mon, 19 Aug 2019 18:34:26 +0800	[thread overview]
Message-ID: <20190819103426.87579-7-gaoxiang25@huawei.com> (raw)
In-Reply-To: <20190819103426.87579-1-gaoxiang25@huawei.com>

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>
---
 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;
-- 
2.17.1

