linux-kernel - [PATCH 2/3] fs: namei: Allow follow

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Date:   Wed,  7 Dec 2022 09:43:08 +0100
From:   Richard Weinberger <richard@....at>
To:     linux-nfs@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        jlayton@...nel.org, chuck.lever@...cle.com, anna@...nel.org,
        trond.myklebust@...merspace.com, viro@...iv.linux.org.uk,
        raven@...maw.net, chris.chilvers@...sbroker.com,
        david.young@...sbroker.com, luis.turcitu@...sbroker.com,
        david@...ma-star.at, benmaynard@...gle.com,
        Richard Weinberger <richard@....at>
Subject: [PATCH 2/3] fs: namei: Allow follow_down() to uncover auto mounts

This function is only used by NFSD to cross mount points.
If a mount point is of type auto mount, follow_down() will
not uncover it. Add LOOKUP_AUTOMOUNT to the lookup flags
to have ->d_automount() called when NFSD walks down the
mount tree.

Signed-off-by: Richard Weinberger <richard@....at>
---
 fs/namei.c            | 6 +++---
 fs/nfsd/vfs.c         | 6 +++++-
 include/linux/namei.h | 2 +-
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 578c2110df02..a6bb6863bf0c 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1458,11 +1458,11 @@ EXPORT_SYMBOL(follow_down_one);
  * point, the filesystem owning that dentry may be queried as to whether the
  * caller is permitted to proceed or not.
  */
-int follow_down(struct path *path)
+int follow_down(struct path *path, unsigned int flags)
 {
 	struct vfsmount *mnt = path->mnt;
 	bool jumped;
-	int ret = traverse_mounts(path, &jumped, NULL, 0);
+	int ret = traverse_mounts(path, &jumped, NULL, flags);
 
 	if (path->mnt != mnt)
 		mntput(mnt);
@@ -2864,7 +2864,7 @@ int path_pts(struct path *path)
 
 	path->dentry = child;
 	dput(parent);
-	follow_down(path);
+	follow_down(path, 0);
 	return 0;
 }
 #endif
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 157f0df0e93a..ced04fc2b947 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -63,9 +63,13 @@ nfsd_cross_mnt(struct svc_rqst *rqstp, struct dentry **dpp,
 	struct dentry *dentry = *dpp;
 	struct path path = {.mnt = mntget(exp->ex_path.mnt),
 			    .dentry = dget(dentry)};
+	unsigned int follow_flags = 0;
 	int err = 0;
 
-	err = follow_down(&path);
+	if (exp->ex_flags & NFSEXP_CROSSMOUNT)
+		follow_flags = LOOKUP_AUTOMOUNT;
+
+	err = follow_down(&path, follow_flags);
 	if (err < 0)
 		goto out;
 	if (path.mnt == exp->ex_path.mnt && path.dentry == dentry &&
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 00fee52df842..6f96db73a70a 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -77,7 +77,7 @@ struct dentry *lookup_one_positive_unlocked(struct user_namespace *mnt_userns,
 					    struct dentry *base, int len);
 
 extern int follow_down_one(struct path *);
-extern int follow_down(struct path *);
+extern int follow_down(struct path *, unsigned int flags);
 extern int follow_up(struct path *);
 
 extern struct dentry *lock_rename(struct dentry *, struct dentry *);
-- 
2.26.2