[PATCH 5.6 215/254] NFS: finish_automount() requires us to hold 2 refs to the mount record

From: Greg Kroah-Hartman
Date: Thu Apr 16 2020 - 10:43:11 EST


From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>

commit 75da98586af75eb80664714a67a9895bf0a5517e upstream.

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@xxxxxxxxxxxxxxx # v5.5+
Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/nfs/namespace.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/fs/nfs/namespace.c
+++ b/fs/nfs/namespace.c
@@ -145,6 +145,7 @@ struct vfsmount *nfs_d_automount(struct
struct vfsmount *mnt = ERR_PTR(-ENOMEM);
struct nfs_server *server = NFS_SERVER(d_inode(path->dentry));
struct nfs_client *client = server->nfs_client;
+ int timeout = READ_ONCE(nfs_mountpoint_expiry_timeout);
int ret;

if (IS_ROOT(path->dentry))
@@ -190,12 +191,12 @@ struct vfsmount *nfs_d_automount(struct
if (IS_ERR(mnt))
goto out_fc;

- if (nfs_mountpoint_expiry_timeout < 0)
+ mntget(mnt); /* prevent immediate expiration */
+ if (timeout <= 0)
goto out_fc;

- 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_fc:
put_fs_context(fc);
@@ -233,10 +234,11 @@ const struct inode_operations nfs_referr
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)