From: Trond Myklebust <trond.myklebust@hammerspace.com>
Date: Thu, 6 Jan 2022 18:24:02 -0500
Subject: [PATCH] NFSv4: Handle case where the lookup of a directory fails
Git-commit: ac795161c93699d600db16c1a8cc23a65a1eceaf
Patch-mainline: v5.17
References: git-fixes

If the application sets the O_DIRECTORY flag, and tries to open a
regular file, nfs_atomic_open() will punt to doing a regular lookup.
If the server then returns a regular file, we will happily return a
file descriptor with uninitialised open state.

The fix is to return the expected ENOTDIR error in these cases.

Reported-by: Lyu Tao <tao.lyu@epfl.ch>
Fixes: 0dd2b474d0b6 ("nfs: implement i_op->atomic_open()")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
Acked-by: NeilBrown <neilb@suse.com>

---
 fs/nfs/dir.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -1657,6 +1657,19 @@ out:
 
 no_open:
 	res = nfs_lookup(dir, dentry, lookup_flags);
+	if (!res) {
+		inode = d_inode(dentry);
+		if ((lookup_flags & LOOKUP_DIRECTORY) && inode &&
+		    !S_ISDIR(inode->i_mode))
+			res = ERR_PTR(-ENOTDIR);
+	} else if (!IS_ERR(res)) {
+		inode = d_inode(res);
+		if ((lookup_flags & LOOKUP_DIRECTORY) && inode &&
+		    !S_ISDIR(inode->i_mode)) {
+			dput(res);
+			res = ERR_PTR(-ENOTDIR);
+		}
+	}
 	if (switched) {
 		d_lookup_done(dentry);
 		if (!res)