Commit 2857bd59 authored by NeilBrown's avatar NeilBrown Committed by Chuck Lever
Browse files

nfsd: provide locking for v4_end_grace 



Writing to v4_end_grace can race with server shutdown and result in
memory being accessed after it was freed - reclaim_str_hashtbl in
particularly.

We cannot hold nfsd_mutex across the nfsd4_end_grace() call as that is
held while client_tracking_op->init() is called and that can wait for
an upcall to nfsdcltrack which can write to v4_end_grace, resulting in a
deadlock.

nfsd4_end_grace() is also called by the landromat work queue and this
doesn't require locking as server shutdown will stop the work and wait
for it before freeing anything that nfsd4_end_grace() might access.

However, we must be sure that writing to v4_end_grace doesn't restart
the work item after shutdown has already waited for it.  For this we
add a new flag protected with nn->client_lock.  It is set only while it
is safe to make client tracking calls, and v4_end_grace only schedules
work while the flag is set with the spinlock held.

So this patch adds a nfsd_net field "client_tracking_active" which is
set as described.  Another field "grace_end_forced", is set when
v4_end_grace is written.  After this is set, and providing
client_tracking_active is set, the laundromat is scheduled.
This "grace_end_forced" field bypasses other checks for whether the
grace period has finished.

This resolves a race which can result in use-after-free.

Reported-by: default avatarLi Lingfeng <lilingfeng3@huawei.com>
Closes: https://lore.kernel.org/linux-nfs/20250623030015.2353515-1-neil@brown.name/T/#t


Fixes: 7f5ef2e9 ("nfsd: add a v4_end_grace file to /proc/fs/nfsd")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarNeilBrown <neil@brown.name>
Tested-by: default avatarLi Lingfeng <lilingfeng3@huawei.com>
Reviewed-by: default avatarJeff Layton <jlayton@kernel.org>
Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
parent e901c7fc

fs/nfsd/netns.h

+2 −0
Original line number Diff line number Diff line
@@ -66,6 +66,8 @@ struct nfsd_net { 


	struct lock_manager nfsd4_manager;

	bool grace_ended;

	bool grace_end_forced;

	bool client_tracking_active;

	time64_t boot_time;



	struct dentry *nfsd_client_dir;

fs/nfsd/nfs4state.c

+40 −2
Original line number Diff line number Diff line
@@ -84,7 +84,7 @@ static u64 current_sessionid = 1; 
/* forward declarations */

static bool check_for_locks(struct nfs4_file *fp, struct nfs4_lockowner *lowner);

static void nfs4_free_ol_stateid(struct nfs4_stid *stid);

void nfsd4_end_grace(struct nfsd_net *nn);

static void nfsd4_end_grace(struct nfsd_net *nn);

static void _free_cpntf_state_locked(struct nfsd_net *nn, struct nfs4_cpntf_state *cps);

static void nfsd4_file_hash_remove(struct nfs4_file *fi);

static void deleg_reaper(struct nfsd_net *nn);
@@ -6570,7 +6570,7 @@ nfsd4_renew(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, 
	return nfs_ok;

}



void

static void

nfsd4_end_grace(struct nfsd_net *nn)

{

	/* do nothing if grace period already ended */
@@ -6603,6 +6603,33 @@ nfsd4_end_grace(struct nfsd_net *nn) 
	 */

}



/**

 * nfsd4_force_end_grace - forcibly end the NFSv4 grace period

 * @nn: network namespace for the server instance to be updated

 *

 * Forces bypass of normal grace period completion, then schedules

 * the laundromat to end the grace period immediately. Does not wait

 * for the grace period to fully terminate before returning.

 *

 * Return values:

 *   %true: Grace termination schedule

 *   %false: No action was taken

 */

bool nfsd4_force_end_grace(struct nfsd_net *nn)

{

	if (!nn->client_tracking_ops)

		return false;

	spin_lock(&nn->client_lock);

	if (nn->grace_ended || !nn->client_tracking_active) {

		spin_unlock(&nn->client_lock);

		return false;

	}

	WRITE_ONCE(nn->grace_end_forced, true);

	mod_delayed_work(laundry_wq, &nn->laundromat_work, 0);

	spin_unlock(&nn->client_lock);

	return true;

}



/*

 * If we've waited a lease period but there are still clients trying to

 * reclaim, wait a little longer to give them a chance to finish.
@@ -6612,6 +6639,8 @@ static bool clients_still_reclaiming(struct nfsd_net *nn) 
	time64_t double_grace_period_end = nn->boot_time +

					   2 * nn->nfsd4_lease;



	if (READ_ONCE(nn->grace_end_forced))

		return false;

	if (nn->track_reclaim_completes &&

			atomic_read(&nn->nr_reclaim_complete) ==

			nn->reclaim_str_hashtbl_size)
@@ -8931,6 +8960,8 @@ static int nfs4_state_create_net(struct net *net) 
	nn->unconf_name_tree = RB_ROOT;

	nn->boot_time = ktime_get_real_seconds();

	nn->grace_ended = false;

	nn->grace_end_forced = false;

	nn->client_tracking_active = false;

	nn->nfsd4_manager.block_opens = true;

	INIT_LIST_HEAD(&nn->nfsd4_manager.list);

	INIT_LIST_HEAD(&nn->client_lru);
@@ -9011,6 +9042,10 @@ nfs4_state_start_net(struct net *net) 
		return ret;

	locks_start_grace(net, &nn->nfsd4_manager);

	nfsd4_client_tracking_init(net);

	/* safe for laundromat to run now */

	spin_lock(&nn->client_lock);

	nn->client_tracking_active = true;

	spin_unlock(&nn->client_lock);

	if (nn->track_reclaim_completes && nn->reclaim_str_hashtbl_size == 0)

		goto skip_grace;

	printk(KERN_INFO "NFSD: starting %lld-second grace period (net %x)\n",
@@ -9059,6 +9094,9 @@ nfs4_state_shutdown_net(struct net *net) 


	shrinker_free(nn->nfsd_client_shrinker);

	cancel_work_sync(&nn->nfsd_shrinker_work);

	spin_lock(&nn->client_lock);

	nn->client_tracking_active = false;

	spin_unlock(&nn->client_lock);

	cancel_delayed_work_sync(&nn->laundromat_work);

	locks_end_grace(&nn->nfsd4_manager);

fs/nfsd/nfsctl.c

+1 −2
Original line number Diff line number Diff line
@@ -1082,10 +1082,9 @@ static ssize_t write_v4_end_grace(struct file *file, char *buf, size_t size) 
		case 'Y':

		case 'y':

		case '1':

			if (!nn->nfsd_serv)

			if (!nfsd4_force_end_grace(nn))

				return -EBUSY;

			trace_nfsd_end_grace(netns(file));

			nfsd4_end_grace(nn);

			break;

		default:

			return -EINVAL;

fs/nfsd/state.h

+1 −1
Original line number Diff line number Diff line
@@ -849,7 +849,7 @@ static inline void nfsd4_revoke_states(struct net *net, struct super_block *sb) 
#endif



/* grace period management */

void nfsd4_end_grace(struct nfsd_net *nn);

bool nfsd4_force_end_grace(struct nfsd_net *nn);



/* nfs4recover operations */

extern int nfsd4_client_tracking_init(struct net *net);