Patch "NFSD: Limit the number of concurrent async COPY operations" has been added to the 6.11-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    NFSD: Limit the number of concurrent async COPY operations

to the 6.11-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nfsd-limit-the-number-of-concurrent-async-copy-opera.patch
and it can be found in the queue-6.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 616f16bf68cf75b449a2432f034abfded43f5979
Author: Chuck Lever <chuck.lever@xxxxxxxxxx>
Date:   Wed Aug 28 13:40:04 2024 -0400

    NFSD: Limit the number of concurrent async COPY operations
    
    [ Upstream commit aadc3bbea163b6caaaebfdd2b6c4667fbc726752 ]
    
    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@xxxxxxxxxxxxxxx
    Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 14ec156563209..5cae26917436c 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 60c526adc27c6..5768b2ff1d1d1 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 +1834,16 @@ 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);
@@ -1876,7 +1883,7 @@ 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;
 	goto out;
 }
 
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index f4eae4b65572a..3837f4e417247 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -8575,6 +8575,7 @@ 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 fbdd42cde1fa5..2a21a7662e030 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)