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@xxxxxxxxxx>
---
fs/nfsd/netns.h | 1 +
fs/nfsd/nfs4state.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++
fs/nfsd/state.h | 2 ++
3 files changed, 65 insertions(+)
diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 5fbf3bbd00d0..b10d557f9c9e 100644
--- 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 ca0db4974e5b..6c74d9a45163 100644
--- 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 @@ out:
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 f6ffeac391f4..abf0fe251f50 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -588,6 +588,8 @@ 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;
--
2.7.4
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