linux-kernel - [PATCH 5.5 251/257] NFS: finish_automount() requires us to hold 2 refs to the mount record

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Date:   Thu, 16 Apr 2020 15:25:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.5 251/257] NFS: finish_automount() requires us to hold 2 refs to the mount record

From: Trond Myklebust <trond.myklebust@...merspace.com>

[ 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@...r.kernel.org # v5.5+
Signed-off-by: Trond Myklebust <trond.myklebust@...merspace.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/nfs/namespace.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index 5e0e9d29f5c57..0c5db17607411 100644
--- 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)
-- 
2.20.1