Re: [RFC PATCH 2/7] NFSD: Limit the number of concurrent async COPY operations

On Wed, 2024-08-28 at 13:40 -0400, cel@kernel.org wrote:

From: Chuck Lever chuck.lever@oracle.com

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 Signed-off-by: Chuck Lever chuck.lever@oracle.com

---

fs/nfsd/netns.h | 1 + fs/nfsd/nfs4proc.c | 12 ++++++++++-- fs/nfsd/nfs4state.c | 1 + fs/nfsd/xdr4.h | 1 + 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h index 14ec15656320..5cae26917436 100644 --- 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 60c526adc27c..27f7eceb3b00 100644 --- a/fs/nfsd/nfs4proc.c +++ b/fs/nfsd/nfs4proc.c @@ -1279,6 +1279,7 @@ 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);

} @@ -1833,10 +1834,17 @@ 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);
  

• /* Arbitrary cap on number of pending async copy operations */
  

• int nrthreads = atomic_read(&rqstp->rq_pool->sp_nrthreads);
  

• async_copy = kzalloc(sizeof(struct nfsd4_copy), GFP_KERNEL); if (!async_copy) goto out_err;

• async_copy->cp_nn = nn;
  

• if (atomic_inc_return(&nn->pending_async_copies) > 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);

@@ -1876,7 +1884,7 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, } if (async_copy) cleanup_async_copy(async_copy);

• status = nfserrno(-ENOMEM);

• status = nfserr_jukebox;

ENOMEM gets translated to nfserr_jukebox anyway, so this doesn't change anything (good).

goto out; } diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index a20c2c9d7d45..aaebc60cc77c 100644 --- 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 fbdd42cde1fa..2a21a7662e03 100644 --- 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)

A per-ns limit sounds like a reasonable place to start.

Reviewed-by: Jeff Layton jlayton@kernel.org