On 2019-11-13, Aleksa Sarai [off-list ref] wrote:

On 2019-11-13, Al Viro [off-list ref] wrote:

quoted

Minor nit here - I'd split "move the conditional call of set_root()
into nd_jump_root()" into a separate patch before that one.  Makes
for fewer distractions in this one.  I'd probably fold "and be
ready for errors other than -ECHILD" into the same preliminary
patch.

Will do.

quoted

quoted

+			/* Not currently safe for scoped-lookups. */
+			if (unlikely(nd->flags & LOOKUP_IS_SCOPED))
+				return ERR_PTR(-EXDEV);

Also a candidate for doing in nd_jump_link()...

quoted

@@ -1373,8 +1403,11 @@ static int follow_dotdot_rcu(struct nameidata *nd)
 	struct inode *inode = nd->inode;
 
 	while (1) {
-		if (path_equal(&nd->path, &nd->root))
+		if (path_equal(&nd->path, &nd->root)) {
+			if (unlikely(nd->flags & LOOKUP_BENEATH))
+				return -EXDEV;

Umm...  Are you sure it's not -ECHILD?

It wouldn't hurt to be -ECHILD -- though it's not clear to me how likely
a success would be in REF-walk if the parent components didn't already
trigger an unlazy_walk() in RCU-walk.

I guess that also means LOOKUP_NO_XDEV should trigger -ECHILD in
follow_dotdot_rcu()?

Scratch the last question -- AFAICS we don't need to do that for
LOOKUP_NO_XDEV because we check against mount_lock so it's very unlikely
that -ECHILD will have any benefit.

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>