nfsd: add a LRU list for blocked locks

It's possible for a client to call in on a lock that is blocked for a
long time, but discontinue polling for it. A malicious client could
even set a lock on a file, and then spam the server with failing lock
requests from different lockowners that pile up in a DoS attack.

Add the blocked lock structures to a per-net namespace LRU when hashing
them, and timestamp them. If the lock request is not revisited after a
lease period, we'll drop it under the assumption that the client is no
longer interested.

This also gives us a mechanism to clean up these objects at server
shutdown time as well.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 5fbf3bbd00d04656f1a459cc6c4027989fbb977e..b10d557f9c9ef0033a6dcbcfcf30141745132e8f 100644 (file)
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -84,6 +84,7 @@ struct nfsd_net {
        struct list_head client_lru;
        struct list_head close_lru;
        struct list_head del_recall_lru;
+       struct list_head blocked_locks_lru;
 
        struct delayed_work laundromat_work;
 

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index ca0db4974e5b194aa9454f19128788c56345212f..6c74d9a45163e1e94bfbda6d577c1f6a57709958 100644 (file)
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -221,6 +221,7 @@ find_blocked_lock(struct nfs4_lockowner *lo, struct knfsd_fh *fh,
        list_for_each_entry(cur, &lo->lo_blocked, nbl_list) {
                if (fh_match(fh, &cur->nbl_fh)) {
                        list_del_init(&cur->nbl_list);
+                       list_del_init(&cur->nbl_lru);
                        found = cur;
                        break;
                }
@@ -4580,6 +4581,7 @@ nfs4_laundromat(struct nfsd_net *nn)
        struct nfs4_openowner *oo;
        struct nfs4_delegation *dp;
        struct nfs4_ol_stateid *stp;
+       struct nfsd4_blocked_lock *nbl;
        struct list_head *pos, *next, reaplist;
        time_t cutoff = get_seconds() - nn->nfsd4_lease;
        time_t t, new_timeo = nn->nfsd4_lease;
@@ -4648,6 +4650,41 @@ nfs4_laundromat(struct nfsd_net *nn)
        }
        spin_unlock(&nn->client_lock);
 
+       /*
+        * It's possible for a client to try and acquire an already held lock
+        * that is being held for a long time, and then lose interest in it.
+        * So, we clean out any un-revisited request after a lease period
+        * under the assumption that the client is no longer interested.
+        *
+        * RFC5661, sec. 9.6 states that the client must not rely on getting
+        * notifications and must continue to poll for locks, even when the
+        * server supports them. Thus this shouldn't lead to clients blocking
+        * indefinitely once the lock does become free.
+        */
+       BUG_ON(!list_empty(&reaplist));
+       spin_lock(&nn->client_lock);
+       while (!list_empty(&nn->blocked_locks_lru)) {
+               nbl = list_first_entry(&nn->blocked_locks_lru,
+                                       struct nfsd4_blocked_lock, nbl_lru);
+               if (time_after((unsigned long)nbl->nbl_time,
+                              (unsigned long)cutoff)) {
+                       t = nbl->nbl_time - cutoff;
+                       new_timeo = min(new_timeo, t);
+                       break;
+               }
+               list_move(&nbl->nbl_lru, &reaplist);
+               list_del_init(&nbl->nbl_list);
+       }
+       spin_unlock(&nn->client_lock);
+
+       while (!list_empty(&reaplist)) {
+               nbl = list_first_entry(&nn->blocked_locks_lru,
+                                       struct nfsd4_blocked_lock, nbl_lru);
+               list_del_init(&nbl->nbl_lru);
+               posix_unblock_lock(&nbl->nbl_lock);
+               free_blocked_lock(nbl);
+       }
+
        new_timeo = max_t(time_t, new_timeo, NFSD_LAUNDROMAT_MINTIMEOUT);
        return new_timeo;
 }
@@ -5398,9 +5435,11 @@ nfsd4_lm_notify(struct file_lock *fl)
                                                struct nfsd4_blocked_lock, nbl_lock);
        bool queue = false;
 
+       /* An empty list means that something else is going to be using it */
        spin_lock(&nn->client_lock);
        if (!list_empty(&nbl->nbl_list)) {
                list_del_init(&nbl->nbl_list);
+               list_del_init(&nbl->nbl_lru);
                queue = true;
        }
        spin_unlock(&nn->client_lock);
@@ -5825,8 +5864,10 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
        }
 
        if (fl_flags & FL_SLEEP) {
+               nbl->nbl_time = jiffies;
                spin_lock(&nn->client_lock);
                list_add_tail(&nbl->nbl_list, &lock_sop->lo_blocked);
+               list_add_tail(&nbl->nbl_lru, &nn->blocked_locks_lru);
                spin_unlock(&nn->client_lock);
        }
 
@@ -5858,6 +5899,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
                if (fl_flags & FL_SLEEP) {
                        spin_lock(&nn->client_lock);
                        list_del_init(&nbl->nbl_list);
+                       list_del_init(&nbl->nbl_lru);
                        spin_unlock(&nn->client_lock);
                }
                free_blocked_lock(nbl);
@@ -6898,6 +6940,7 @@ static int nfs4_state_create_net(struct net *net)
        INIT_LIST_HEAD(&nn->client_lru);
        INIT_LIST_HEAD(&nn->close_lru);
        INIT_LIST_HEAD(&nn->del_recall_lru);
+       INIT_LIST_HEAD(&nn->blocked_locks_lru);
        spin_lock_init(&nn->client_lock);
 
        INIT_DELAYED_WORK(&nn->laundromat_work, laundromat_main);
@@ -6995,6 +7038,7 @@ nfs4_state_shutdown_net(struct net *net)
        struct nfs4_delegation *dp = NULL;
        struct list_head *pos, *next, reaplist;
        struct nfsd_net *nn = net_generic(net, nfsd_net_id);
+       struct nfsd4_blocked_lock *nbl;
 
        cancel_delayed_work_sync(&nn->laundromat_work);
        locks_end_grace(&nn->nfsd4_manager);
@@ -7015,6 +7059,24 @@ nfs4_state_shutdown_net(struct net *net)
                nfs4_put_stid(&dp->dl_stid);
        }
 
+       BUG_ON(!list_empty(&reaplist));
+       spin_lock(&nn->client_lock);
+       while (!list_empty(&nn->blocked_locks_lru)) {
+               nbl = list_first_entry(&nn->blocked_locks_lru,
+                                       struct nfsd4_blocked_lock, nbl_lru);
+               list_move(&nbl->nbl_lru, &reaplist);
+               list_del_init(&nbl->nbl_list);
+       }
+       spin_unlock(&nn->client_lock);
+
+       while (!list_empty(&reaplist)) {
+               nbl = list_first_entry(&nn->blocked_locks_lru,
+                                       struct nfsd4_blocked_lock, nbl_lru);
+               list_del_init(&nbl->nbl_lru);
+               posix_unblock_lock(&nbl->nbl_lock);
+               free_blocked_lock(nbl);
+       }
+
        nfsd4_client_tracking_exit(net);
        nfs4_state_destroy_net(net);
 }

diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index e45c183a8bf79a25a4ff37781587b49213af7156..c9399366f9dfc73b343d079fbad2dc2127927aae 100644 (file)
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -587,6 +587,8 @@ static inline bool nfsd4_stateid_generation_after(stateid_t *a, stateid_t *b)
  */
 struct nfsd4_blocked_lock {
        struct list_head        nbl_list;
+       struct list_head        nbl_lru;
+       unsigned long           nbl_time;
        struct file_lock        nbl_lock;
        struct knfsd_fh         nbl_fh;
        struct nfsd4_callback   nbl_cb;