[PATCH v6] xfs: introduce protection for drop nlink

[PATCH v6] xfs: introduce protection for drop nlink

[cheng.lin130]

From: Cheng Lin <cheng.lin130@zte.com.cn>

When abnormal drop_nlink are detected on the inode,
return error, to avoid corruption propagation.

Signed-off-by: Cheng Lin <cheng.lin130@zte.com.cn>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
---
 fs/xfs/xfs_inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 9e62cc500..0fa1ac5e0 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -919,6 +919,13 @@ xfs_droplink(
 	xfs_trans_t *tp,
 	xfs_inode_t *ip)
 {
+	if (VFS_I(ip)->i_nlink == 0) {
+		xfs_alert(ip->i_mount,
+			  "%s: Attempt to drop inode (%llu) with nlink zero.",
+			  __func__, ip->i_ino);
+		return -EFSCORRUPTED;
+	}
+
 	xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG);

 	drop_nlink(VFS_I(ip));
-- 
2.18.1

Re: [PATCH v6] xfs: introduce protection for drop nlink

[Christoph Hellwig]

On Tue, Oct 10, 2023 at 10:09:01AM +0800, cheng.lin130@zte.com.cn wrote:
> From: Cheng Lin <cheng.lin130@zte.com.cn>
> 
> When abnormal drop_nlink are detected on the inode,
> return error, to avoid corruption propagation.

I know this has been through a few cycles, but wouldn't it be useful
to have at least a little description here how that case could happen?

Re: [PATCH v6] xfs: introduce protection for drop nlink

[cheng.lin130]

> On Tue, Oct 10, 2023 at 10:09:01AM +0800, cheng.lin130@zte.com.cn wrote:
> > From: Cheng Lin <cheng.lin130@zte.com.cn>
> > 
> > When abnormal drop_nlink are detected on the inode,
> > return error, to avoid corruption propagation.
> I know this has been through a few cycles, but wouldn't it be useful
> to have at least a little description here how that case could happen?
Unfortunately, I don't know how the underflow happened. The purpose
of this patch is to prevent the situation from getting worse and provide
users can repair it at the appropriate moment afterwards.