[PATCH] ovl: relax lookup error on mismatch origin ftype

[Amir Goldstein <amir73il@gmail.com>]

We get occasional reports of lookup errors due to mismatched
origin ftype from users that re-format a lower squashfs image.

Commit 13c6ad0f45fd ("ovl: document lower modification caveats")
tries to discourage the practice of re-formating lower layers and
describes the expected behavior as undefined.

Commit b0e0f69731cd ("ovl: restrict lower null uuid for "xino=auto"")
limits the configurations in which origin file handles are followed.

In addition to these measures, change the behavior in case of detecting
a mismatch origin ftype in lookup to issue a warning, not follow origin,
but not fail the lookup operation either.

That should make overall more users happy without any big consequences.

Link: https://lore.kernel.org/linux-unionfs/CAOQ4uxgPq9E9xxwU2CDyHy-_yCZZeymg+3n+-6AqkGGE1YtwvQ@mail.gmail.com/
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---

Miklos,

I am getting tired of dealing with lower squashfs related reports.
How about this?

It passes the xfstests quick tests and no, I do not have a reproducer
for origin mismatch, so will wait for Byron to test the patch.

Thanks,
Amir.

 fs/overlayfs/namei.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 71e264e2f16b..850c0a37f1f0 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -392,7 +392,7 @@ int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
 			    upperdentry, d_inode(upperdentry)->i_mode & S_IFMT,
 			    d_inode(origin)->i_mode & S_IFMT);
 	dput(origin);
-	return -EIO;
+	return -EINVAL;
 }
 
 static int ovl_check_origin(struct ovl_fs *ofs, struct dentry *upperdentry,
@@ -408,7 +408,7 @@ static int ovl_check_origin(struct ovl_fs *ofs, struct dentry *upperdentry,
 	kfree(fh);
 
 	if (err) {
-		if (err == -ESTALE)
+		if (err == -ESTALE || err == -EINVAL)
 			return 0;
 		return err;
 	}
-- 
2.25.1