[RFC PATCH v2] fs: introduce check for inode nlink when delete

[<cheng.lin130@xxxxxxxxxx>]

From: Cheng Lin <cheng.lin130@xxxxxxxxxx>

Do not delete inode which nlink already zero to avoid
inode nlink underflow.

Signed-off-by: Cheng Lin <cheng.lin130@xxxxxxxxxx>
---
 fs/namei.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index e56ff39a7..30bc0d0a6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4197,6 +4197,11 @@ int vfs_rmdir(struct mnt_idmap *idmap, struct inode *dir,
 	if (error)
 		goto out;

+	if (unlikely(dir->i_nlink == 0) ||
+	    unlikely(dentry->d_inode->i_nlink == 0)) {
+		error = -EUCLEAN;
+		goto out;
+	}
 	error = dir->i_op->rmdir(dir, dentry);
 	if (error)
 		goto out;
@@ -4326,6 +4331,10 @@ int vfs_unlink(struct mnt_idmap *idmap, struct inode *dir,
 			error = try_break_deleg(target, delegated_inode);
 			if (error)
 				goto out;
+			if (unlikely(target->i_nlink == 0)) {
+				error = -EUCLEAN;
+				goto out;
+			}
 			error = dir->i_op->unlink(dir, dentry);
 			if (!error) {
 				dont_mount(dentry);
-- 
2.18.1