linux-kernel - [PATCH] erofs: fix order >= MAX_ORDER warning due to crafted nagative i

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Date:   Fri,  9 Sep 2022 10:39:48 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     linux-erofs@...ts.ozlabs.org
Cc:     LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Gao Xiang <hsiangkao@...ux.alibaba.com>,
        syzbot+f966c13b1b4fc0403b19@...kaller.appspotmail.com
Subject: [PATCH] erofs: fix order >= MAX_ORDER warning due to crafted nagative i_size

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@...kaller.appspotmail.com
Fixes: 431339ba9042 ("staging: erofs: add inode operations")
Signed-off-by: Gao Xiang <hsiangkao@...ux.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 95a403720e8c..16cf9a283557 100644
--- a/fs/erofs/inode.c
+++ b/fs/erofs/inode.c
@@ -214,7 +214,7 @@ static int erofs_fill_symlink(struct inode *inode, void *kaddr,
 
 	/* if it cannot be handled with fast symlink scheme */
 	if (vi->datalayout != EROFS_INODE_FLAT_INLINE ||
-	    inode->i_size >= EROFS_BLKSIZ) {
+	    inode->i_size >= EROFS_BLKSIZ || inode->i_size < 0) {
 		inode->i_op = &erofs_symlink_iops;
 		return 0;
 	}
-- 
2.24.4