[PATCH net-next 3/4] netdev: avoid skipping objects on race with device disappearance

[Jakub Kicinski <kuba@kernel.org>]

If the currently dumped device disappears while we were mid-dump
we will get the next device without resetting the sub-object ID.
This is quite unlikely, it was reported by an AI tool not a real
user. Let's fix it for better dump consistency.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 net/core/netdev-genl.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index d35af460e886..18046ad0f883 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -310,11 +310,14 @@ int netdev_nl_napi_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 			err = -ENODEV;
 		}
 	} else {
+		unsigned long start_ifindex = ctx->ifindex;
+
 		for_each_netdev_lock_scoped(net, netdev, ctx->ifindex) {
+			if (ctx->ifindex != start_ifindex)
+				ctx->napi_id = 0;
 			err = netdev_nl_napi_dump_one(netdev, skb, info, ctx);
 			if (err < 0)
 				break;
-			ctx->napi_id = 0;
 		}
 	}
 
@@ -634,13 +637,17 @@ int netdev_nl_queue_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
 			err = -ENODEV;
 		}
 	} else {
+		unsigned long start_ifindex = ctx->ifindex;
+
 		for_each_netdev_lock_ops_compat_scoped(net, netdev,
 						       ctx->ifindex) {
+			if (ctx->ifindex != start_ifindex) {
+				ctx->rxq_idx = 0;
+				ctx->txq_idx = 0;
+			}
 			err = netdev_nl_queue_dump_one(netdev, skb, info, ctx);
 			if (err < 0)
 				break;
-			ctx->rxq_idx = 0;
-			ctx->txq_idx = 0;
 		}
 	}
 
@@ -786,8 +793,6 @@ netdev_nl_stats_by_queue(struct net_device *netdev, struct sk_buff *rsp,
 		ctx->txq_idx = ++i;
 	}
 
-	ctx->rxq_idx = 0;
-	ctx->txq_idx = 0;
 	return 0;
 }
 
@@ -902,6 +907,7 @@ int netdev_nl_qstats_get_dumpit(struct sk_buff *skb,
 	struct netdev_nl_dump_ctx *ctx = netdev_dump_ctx(cb);
 	const struct genl_info *info = genl_info_dump(cb);
 	struct net *net = sock_net(skb->sk);
+	unsigned long start_ifindex;
 	struct net_device *netdev;
 	unsigned int ifindex;
 	unsigned int scope;
@@ -934,7 +940,13 @@ int netdev_nl_qstats_get_dumpit(struct sk_buff *skb,
 		return err;
 	}
 
+	start_ifindex = ctx->ifindex;
+
 	for_each_netdev_lock_ops_compat_scoped(net, netdev, ctx->ifindex) {
+		if (ctx->ifindex != start_ifindex) {
+			ctx->rxq_idx = 0;
+			ctx->txq_idx = 0;
+		}
 		err = netdev_nl_qstats_get_dump_one(netdev, scope, skb,
 						    info, ctx);
 		if (err < 0)
-- 
2.54.0