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nfsd: add a LRU list for blocked locks

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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>
This commit is contained in:
Jeff Layton 2016-09-16 16:28:25 -04:00 committed by J. Bruce Fields
parent 76d348fadf
commit 7919d0a27f
3 changed files with 65 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

1
fs/nfsd/netns.h
View file

@ -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;

62
fs/nfsd/nfs4state.c
View file

@ -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);
}

2
fs/nfsd/state.h
View file

@ -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;