[PATCH v2] nfsd: Invoke tracking callbacks only after initialization is complete

[Li Lingfeng]

Checking whether tracking callbacks can be called based on whether
nn->client_tracking_ops is NULL may lead to callbacks being invoked
before tracking initialization completes, causing resource access
violations (UAF, NULL pointer dereference). Examples:

1) nfsd4_client_tracking_init
   // set nn->client_tracking_ops
   nfsd4_cld_tracking_init
    nfs4_cld_state_init
     nn->reclaim_str_hashtbl = kmalloc_array
    ... // error path, goto err
    nfs4_cld_state_shutdown
     kfree(nn->reclaim_str_hashtbl)
                                      write_v4_end_grace
                                       nfsd4_end_grace
                                        nfsd4_record_grace_done
                                         nfsd4_cld_grace_done
                                          nfs4_release_reclaim
                                           nn->reclaim_str_hashtbl[i]
                                           // UAF
   // clear nn->client_tracking_ops

2) nfsd4_client_tracking_init
   // set nn->client_tracking_ops
   nfsd4_cld_tracking_init
                                      write_v4_end_grace
                                       nfsd4_end_grace
                                        nfsd4_record_grace_done
                                         nfsd4_cld_grace_done
                                          alloc_cld_upcall
                                           cn = nn->cld_net
                                           spin_lock // cn->cn_lock
                                           // NULL deref
   // error path, skip init pipe
   __nfsd4_init_cld_pipe
    cn = kzalloc
    nn->cld_net = cn
   // clear nn->client_tracking_ops

After nfsd mounts, users can trigger grace_done callbacks via
/proc/fs/nfsd/v4_end_grace. If resources are uninitialized or freed
in error paths, this causes access violations.

Resolve the issue by leveraging nfsd_mutex to prevent concurrency.

Fixes: 52e19c09a183 ("nfsd: make reclaim_str_hashtbl allocated per net")
Signed-off-by: Li Lingfeng <lilingfeng3@xxxxxxxxxx>
---
  Changes in v2:
    Use nfsd_mutex instead of adding a new flag to prevent concurrency.
 fs/nfsd/nfs4recover.c | 8 ++++++++
 fs/nfsd/nfs4state.c   | 4 ++++
 fs/nfsd/nfsctl.c      | 2 ++
 3 files changed, 14 insertions(+)

diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 82785db730d9..8ac089f8134c 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -162,7 +162,9 @@ legacy_recdir_name_error(struct nfs4_client *clp, int error)
 	if (error == -ENOENT) {
 		printk(KERN_ERR "NFSD: disabling legacy clientid tracking. "
 			"Reboot recovery will not function correctly!\n");
+		mutex_lock(&nfsd_mutex);
 		nfsd4_client_tracking_exit(clp->net);
+		mutex_unlock(&nfsd_mutex);
 	}
 }
 
@@ -2083,8 +2085,10 @@ nfsd4_client_record_create(struct nfs4_client *clp)
 {
 	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
 
+	mutex_lock(&nfsd_mutex);
 	if (nn->client_tracking_ops)
 		nn->client_tracking_ops->create(clp);
+	mutex_unlock(&nfsd_mutex);
 }
 
 void
@@ -2092,8 +2096,10 @@ nfsd4_client_record_remove(struct nfs4_client *clp)
 {
 	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
 
+	mutex_lock(&nfsd_mutex);
 	if (nn->client_tracking_ops)
 		nn->client_tracking_ops->remove(clp);
+	mutex_unlock(&nfsd_mutex);
 }
 
 int
@@ -2101,8 +2107,10 @@ nfsd4_client_record_check(struct nfs4_client *clp)
 {
 	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
 
+	mutex_lock(&nfsd_mutex);
 	if (nn->client_tracking_ops)
 		return nn->client_tracking_ops->check(clp);
+	mutex_unlock(&nfsd_mutex);
 
 	return -EOPNOTSUPP;
 }
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index d5694987f86f..2794fdc8b678 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -2529,7 +2529,9 @@ static void inc_reclaim_complete(struct nfs4_client *clp)
 			nn->reclaim_str_hashtbl_size) {
 		printk(KERN_INFO "NFSD: all clients done reclaiming, ending NFSv4 grace period (net %x)\n",
 				clp->net->ns.inum);
+		mutex_lock(&nfsd_mutex);
 		nfsd4_end_grace(nn);
+		mutex_unlock(&nfsd_mutex);
 	}
 }
 
@@ -6773,7 +6775,9 @@ nfs4_laundromat(struct nfsd_net *nn)
 		lt.new_timeo = 0;
 		goto out;
 	}
+	mutex_lock(&nfsd_mutex);
 	nfsd4_end_grace(nn);
+	mutex_unlock(&nfsd_mutex);
 
 	spin_lock(&nn->s2s_cp_lock);
 	idr_for_each_entry(&nn->s2s_cp_stateids, cps_t, i) {
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 3f3e9f6c4250..649850b4bb60 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1085,7 +1085,9 @@ static ssize_t write_v4_end_grace(struct file *file, char *buf, size_t size)
 			if (!nn->nfsd_serv)
 				return -EBUSY;
 			trace_nfsd_end_grace(netns(file));
+			mutex_lock(&nfsd_mutex);
 			nfsd4_end_grace(nn);
+			mutex_lock(&nfsd_mutex);
 			break;
 		default:
 			return -EINVAL;
-- 
2.46.1