From 7919d0a27f1e7cb324e023776aa1cbff00f1ee7b Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Fri, 16 Sep 2016 16:28:25 -0400 Subject: 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 Signed-off-by: J. Bruce Fields diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h index 5fbf3bb..b10d557 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 ca0db49..6c74d9a 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 e45c183..c939936 100644 --- 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; -- cgit v0.10.2