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>

diff --git a/drivers/staging/erofs/zmap.c b/drivers/staging/erofs/zmap.c
index 7408e86823a4d41a2bfeceed4016ea6e905aaf7b..774dacbc5b323f6a8f2a981ec997e64f9cb67faf 100644 (file)
--- 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;