NFSD: Limit the number of concurrent async COPY operations

Nothing appears to limit the number of concurrent async COPY
operations that clients can start. In addition, AFAICT each async
COPY can copy an unlimited number of 4MB chunks, so can run for a
long time. Thus IMO async COPY can become a DoS vector.

Add a restriction mechanism that bounds the number of concurrent
background COPY operations. Start simple and try to be fair -- this
patch implements a per-namespace limit.

An async COPY request that occurs while this limit is exceeded gets
NFS4ERR_DELAY. The requesting client can choose to send the request
again after a delay or fall back to a traditional read/write style
copy.

If there is need to make the mechanism more sophisticated, we can
visit that in future patches.

Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 238fc4e..37b8bfd 100644 (file)
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -148,6 +148,7 @@ struct nfsd_net {
        u32             s2s_cp_cl_id;
        struct idr      s2s_cp_stateids;
        spinlock_t      s2s_cp_lock;
+       atomic_t        pending_async_copies;
 
        /*
         * Version information

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 231c603..9655acb 100644 (file)
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1280,6 +1280,7 @@ static void nfs4_put_copy(struct nfsd4_copy *copy)
 {
        if (!refcount_dec_and_test(&copy->refcount))
                return;
+       atomic_dec(&copy->cp_nn->pending_async_copies);
        kfree(copy->cp_src);
        kfree(copy);
 }
@@ -1835,10 +1836,16 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
        memcpy(&copy->fh, &cstate->current_fh.fh_handle,
                sizeof(struct knfsd_fh));
        if (nfsd4_copy_is_async(copy)) {
-               status = nfserrno(-ENOMEM);
                async_copy = kzalloc(sizeof(struct nfsd4_copy), GFP_KERNEL);
                if (!async_copy)
                        goto out_err;
+               async_copy->cp_nn = nn;
+               /* Arbitrary cap on number of pending async copy operations */
+               if (atomic_inc_return(&nn->pending_async_copies) >
+                               (int)rqstp->rq_pool->sp_nrthreads) {
+                       atomic_dec(&nn->pending_async_copies);
+                       goto out_err;
+               }
                INIT_LIST_HEAD(&async_copy->copies);
                refcount_set(&async_copy->refcount, 1);
                async_copy->cp_src = kmalloc(sizeof(*async_copy->cp_src), GFP_KERNEL);
@@ -1878,7 +1885,7 @@ out_err:
        }
        if (async_copy)
                cleanup_async_copy(async_copy);
-       status = nfserrno(-ENOMEM);
+       status = nfserr_jukebox;
        goto out;
 }
 

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 7ade551..a49aa75 100644 (file)
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -8554,6 +8554,7 @@ static int nfs4_state_create_net(struct net *net)
        spin_lock_init(&nn->client_lock);
        spin_lock_init(&nn->s2s_cp_lock);
        idr_init(&nn->s2s_cp_stateids);
+       atomic_set(&nn->pending_async_copies, 0);
 
        spin_lock_init(&nn->blocked_locks_lock);
        INIT_LIST_HEAD(&nn->blocked_locks_lru);

diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
index fbdd42c..2a21a76 100644 (file)
--- a/fs/nfsd/xdr4.h
+++ b/fs/nfsd/xdr4.h
@@ -713,6 +713,7 @@ struct nfsd4_copy {
        struct nfsd4_ssc_umount_item *ss_nsui;
        struct nfs_fh           c_fh;
        nfs4_stateid            stateid;
+       struct nfsd_net         *cp_nn;
 };
 
 static inline void nfsd4_copy_set_sync(struct nfsd4_copy *copy, bool sync)