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

commit 598bb8913d015150b7734b55443c0e53e7189fc7 upstream.

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
[ Gao Xiang: Since earlier kernels don't define EFSCORRUPTED,
             let's use EIO instead. ]
Signed-off-by: Gao Xiang <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 c2359321ca134701332aeb2aaa7a379cfbfe540f..30e6d02d30de7ff571078fc0d0a666ffabea99d0 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 (!m->delta[0]) {
+                       errln("invalid lookback distance 0 at nid %llu",
+                             vi->nid);
+                       DBG_BUGON(1);
+                       return -EIO;
+               }
                return vle_extent_lookback(m, m->delta[0]);
        case Z_EROFS_VLE_CLUSTER_TYPE_PLAIN:
                map->m_flags &= ~EROFS_MAP_ZIPPED;