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 238fc4e56e539715d437a0bd9034f1dbb8ecf77e..37b8bfdcfeea8ec4a1f75afdf353b6bba5d4c40c 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 231c6035602f6b1a45214d92760ac641c813c15a..9655acb407b728bfe7318139f79909b104e13b5f 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 7ade551bc02211b5603cf31a3d743ba5c4058a48..a49aa75bc0b797aaf96840e8e5470dbeb565fa12 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 fbdd42cde1fa5bc6ed7df1aec685dd111b50263c..2a21a7662e030cbd0f54060edd2b91e4d8c86d7e 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)