[PATCH v2 03/21] nfsd: fix netlink dumpit error handling for rpc_status_get

[Jeff Layton <jlayton@kernel.org>]

nfsd_genl_rpc_status_compose_msg() returns -ENOBUFS on nla_put failure
without calling genlmsg_cancel(), leaving a partial message in the skb.
The caller then propagates -ENOBUFS directly, which the netlink dump
infrastructure treats as a fatal error, aborting the entire dump.

The correct netlink dump convention is:
 - Cancel any partial message with genlmsg_cancel()
 - If prior messages were added to the skb (skb->len > 0), save the
   current iterator position and return skb->len to paginate
 - Only return a negative errno when no messages fit at all

Fix compose_msg to cancel the partial message on all nla_put failure
paths, and fix the caller to paginate when possible rather than
returning a fatal error.

Fixes: ac18892ea3f7 ("NFSD: add rpc_status netlink support")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/nfsd/nfsctl.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index a4b5b1467fe2..ab10692ee937 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1452,7 +1452,7 @@ static int nfsd_genl_rpc_status_compose_msg(struct sk_buff *skb,
 	    nla_put_s64(skb, NFSD_A_RPC_STATUS_SERVICE_TIME,
 			ktime_to_us(genl_rqstp->rq_stime),
 			NFSD_A_RPC_STATUS_PAD))
-		return -ENOBUFS;
+		goto out_cancel;
 
 	switch (genl_rqstp->rq_saddr.ss_family) {
 	case AF_INET: {
@@ -1468,7 +1468,7 @@ static int nfsd_genl_rpc_status_compose_msg(struct sk_buff *skb,
 				 s_in->sin_port) ||
 		    nla_put_be16(skb, NFSD_A_RPC_STATUS_DPORT,
 				 d_in->sin_port))
-			return -ENOBUFS;
+			goto out_cancel;
 		break;
 	}
 	case AF_INET6: {
@@ -1484,7 +1484,7 @@ static int nfsd_genl_rpc_status_compose_msg(struct sk_buff *skb,
 				 s_in->sin6_port) ||
 		    nla_put_be16(skb, NFSD_A_RPC_STATUS_DPORT,
 				 d_in->sin6_port))
-			return -ENOBUFS;
+			goto out_cancel;
 		break;
 	}
 	}
@@ -1492,10 +1492,14 @@ static int nfsd_genl_rpc_status_compose_msg(struct sk_buff *skb,
 	for (i = 0; i < genl_rqstp->rq_opcnt; i++)
 		if (nla_put_u32(skb, NFSD_A_RPC_STATUS_COMPOUND_OPS,
 				genl_rqstp->rq_opnum[i]))
-			return -ENOBUFS;
+			goto out_cancel;
 
 	genlmsg_end(skb, hdr);
 	return 0;
+
+out_cancel:
+	genlmsg_cancel(skb, hdr);
+	return -ENOBUFS;
 }
 
 /**
@@ -1587,8 +1591,14 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
 
 			ret = nfsd_genl_rpc_status_compose_msg(skb, cb,
 							       &genl_rqstp);
-			if (ret)
+			if (ret) {
+				if (skb->len) {
+					cb->args[0] = i;
+					cb->args[1] = rqstp_index - 1;
+					ret = skb->len;
+				}
 				goto out;
+			}
 		}
 	}
 

-- 
2.54.0