[PATCH 5.15.y 2/2] exportfs: support idmapped mounts

[Christian Brauner <brauner@kernel.org>]

Make the two locations where exportfs helpers check permission to lookup
a given inode idmapped mount aware by switching it to the lookup_one()
helper. This is a bugfix for the open_by_handle_at() system call which
doesn't take idmapped mounts into account currently. It's not tied to a
specific commit so we'll just Cc stable.

In addition this is required to support idmapped base layers in overlay.
The overlay filesystem uses exportfs to encode and decode file handles
for its index=on mount option and when nfs_export=on.

Cc: <stable@vger.kernel.org>
Cc: <linux-fsdevel@vger.kernel.org>
Tested-by: Giuseppe Scrivano <gscrivan@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
---
Hey Greg,

This was missing a preliminary commit.
My build machines are currently down so I couldn't do a test build but
this should build cleanly.

Thanks!
Christian
---
 fs/exportfs/expfs.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
index 0106eba46d5a..3ef80d000e13 100644
--- a/fs/exportfs/expfs.c
+++ b/fs/exportfs/expfs.c
@@ -145,7 +145,7 @@ static struct dentry *reconnect_one(struct vfsmount *mnt,
 	if (err)
 		goto out_err;
 	dprintk("%s: found name: %s\n", __func__, nbuf);
-	tmp = lookup_one_len_unlocked(nbuf, parent, strlen(nbuf));
+	tmp = lookup_one_unlocked(mnt_user_ns(mnt), nbuf, parent, strlen(nbuf));
 	if (IS_ERR(tmp)) {
 		dprintk("%s: lookup failed: %d\n", __func__, PTR_ERR(tmp));
 		err = PTR_ERR(tmp);
@@ -525,7 +525,8 @@ exportfs_decode_fh_raw(struct vfsmount *mnt, struct fid *fid, int fh_len,
 		}
 
 		inode_lock(target_dir->d_inode);
-		nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf));
+		nresult = lookup_one(mnt_user_ns(mnt), nbuf,
+				     target_dir, strlen(nbuf));
 		if (!IS_ERR(nresult)) {
 			if (unlikely(nresult->d_inode != result->d_inode)) {
 				dput(nresult);
-- 
2.34.1