[PATCH] erofs: refuse crafted out-of-file-range encoded extents

[Gao Xiang]

Crafted encoded extents could record out-of-range `lstart`, which should
not happen in normal cases.

It caused an iomap_iter_done() complaint [1] reported by syzbot.

[1] https://lore.kernel.org/r/684cb499.a00a0220.c6bd7.0010.GAE@xxxxxxxxxx
Fixes: 1d191b4ca51d ("erofs: implement encoded extent metadata")
Reported-by: syzbot+d8f000c609f05f52d9b5@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=d8f000c609f05f52d9b5
Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
---
 fs/erofs/zmap.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index 14ea47f954f5..6afcb054780d 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -597,6 +597,10 @@ static int z_erofs_map_blocks_ext(struct inode *inode,
 
 			if (la > map->m_la) {
 				r = mid;
+				if (la > lend) {
+					DBG_BUGON(1);
+					return -EFSCORRUPTED;
+				}
 				lend = la;
 			} else {
 				l = mid + 1;
-- 
2.43.5