Thread (30 messages) 30 messages, 4 authors, 2019-11-14

Re: [PATCH v15 4/9] namei: LOOKUP_BENEATH: O_BENEATH-like scoped resolution

From: Aleksa Sarai <hidden>
Date: 2019-11-14 04:58:19
Also in: linux-alpha, linux-arch, linux-arm-kernel, linux-fsdevel, linux-kselftest, linux-mips, linux-s390, linux-sh, linuxppc-dev, lkml, sparclinux

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/>

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