[PATCH 5.4.y 1/2] erofs: fix order >= MAX_ORDER warning due to crafted negative i_size

[Gao Xiang]

commit 1dd73601a1cba37a0ed5f89a8662c90191df5873 upstream.

As syzbot reported [1], the root cause is that i_size field is a
signed type, and negative i_size is also less than EROFS_BLKSIZ.
As a consequence, it's handled as fast symlink unexpectedly.

Let's fall back to the generic path to deal with such unusual i_size.

[1] https://lore.kernel.org/r/000000000000ac8efa05e7feaa1f@google.com

Reported-by: syzbot+f966c13b1b4fc0403b19 at syzkaller.appspotmail.com
Fixes: 431339ba9042 ("staging: erofs: add inode operations")
Reviewed-by: Yue Hu <huyue2 at coolpad.com>
Link: https://lore.kernel.org/r/20220909023948.28925-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
---
 fs/erofs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
index 0dbeaf68e1d6..ba981076d6f2 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -202,7 +202,7 @@ static int erofs_fill_symlink(struct inode *inode, void *data,
 
 	/* if it cannot be handled with fast symlink scheme */
 	if (vi->datalayout != EROFS_INODE_FLAT_INLINE ||
-	    inode->i_size >= PAGE_SIZE) {
+	    inode->i_size >= PAGE_SIZE || inode->i_size < 0) {
 		inode->i_op = &erofs_symlink_iops;
 		return 0;
 	}
-- 
2.43.5