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SubjectRe: [PATCH v9 05/10] namei: O_BENEATH-style path resolution flags
On Sun, Jul 07, 2019 at 12:57:32AM +1000, Aleksa Sarai wrote:

> @@ -1442,8 +1464,11 @@ 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;

> @@ -1468,6 +1493,8 @@ static int follow_dotdot_rcu(struct nameidata *nd)
> return -ECHILD;
> if (&mparent->mnt == nd->path.mnt)
> break;
> + if (unlikely(nd->flags & LOOKUP_XDEV))
> + return -EXDEV;
> /* we know that mountpoint was pinned */
> nd->path.dentry = mountpoint;
> nd->path.mnt = &mparent->mnt;
> @@ -1482,6 +1509,8 @@ static int follow_dotdot_rcu(struct nameidata *nd)
> return -ECHILD;
> if (!mounted)
> break;
> + if (unlikely(nd->flags & LOOKUP_XDEV))
> + return -EXDEV;

Are you sure these failure exits in follow_dotdot_rcu() won't give
suprious hard errors?

> + if (unlikely(nd->flags & LOOKUP_BENEATH)) {
> + error = dirfd_path_init(nd);
> + if (unlikely(error))
> + return ERR_PTR(error);
> + nd->root = nd->path;
> + if (!(nd->flags & LOOKUP_RCU))
> + path_get(&nd->root);
> + }
> if (*s == '/') {
> if (likely(!nd->root.mnt))
> set_root(nd);
> @@ -2350,9 +2400,11 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
> s = ERR_PTR(error);
> return s;
> }
> - error = dirfd_path_init(nd);
> - if (unlikely(error))
> - return ERR_PTR(error);
> + if (likely(!nd->path.mnt)) {

Is that a weird way of saying "if we hadn't already called dirfd_path_init()"?

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