NFS: finish_automount() requires us to hold 2 refs to the mount record

[ Upstream commit 75da98586af75eb80664714a67a9895bf0a5517e ]

We must not return from nfs_d_automount() without holding 2 references
to the mount record. Doing so, will trigger the BUG() in finish_automount().
Also ensure that we don't try to reschedule the automount timer with
a negative or zero timeout value.

Fixes: 22a1ae9a93fb ("NFS: If nfs_mountpoint_expiry_timeout < 0, do not expire submounts")
Cc: stable@vger.kernel.org # v5.5+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index 5e0e9d29f5c57f91a7ab1956d5ff740afd18e3be..0c5db17607411efc7f4584ed2e74a025f31a9beb 100644 (file)
--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -143,6 +143,7 @@ struct vfsmount *nfs_d_automount(struct path *path)
        struct nfs_server *server = NFS_SERVER(d_inode(path->dentry));
        struct nfs_fh *fh = NULL;
        struct nfs_fattr *fattr = NULL;
+       int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
 
        if (IS_ROOT(path->dentry))
                return ERR_PTR(-ESTALE);
@@ -157,12 +158,12 @@ struct vfsmount *nfs_d_automount(struct path *path)
        if (IS_ERR(mnt))
                goto out;
 
-       if (nfs_mountpoint_expiry_timeout < 0)
+       mntget(mnt); /* prevent immediate expiration */
+       if (timeout <= 0)
                goto out;
 
-       mntget(mnt); /* prevent immediate expiration */
        mnt_set_expiry(mnt, &nfs_automount_list);
-       schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
+       schedule_delayed_work(&nfs_automount_task, timeout);
 
 out:
        nfs_free_fattr(fattr);
@@ -201,10 +202,11 @@ const struct inode_operations nfs_referral_inode_operations = {
 static void nfs_expire_automounts(struct work_struct *work)
 {
        struct list_head *list = &nfs_automount_list;
+       int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
 
        mark_mounts_for_expiry(list);
-       if (!list_empty(list))
-               schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
+       if (!list_empty(list) && timeout > 0)
+               schedule_delayed_work(&nfs_automount_task, timeout);
 }
 
 void nfs_release_automount_timer(void)