[PATCH nf,v2] net: update dev_fill_forward_path() to handle mac80211 special case

[Pablo Neira Ayuso <pablo@netfilter.org>]

Before commit b5964aac51e0 ("netfilter: flowtable: consolidate xmit
path"), there was a fallback to create a bypass in case
.ndo_fill_forward_path fails.

Commit d787a3e38f01 ("mac80211: add support for .ndo_fill_forward_path")
relies on such fallback, so most mac80211 drivers used to work since
they do not provide a net_fill_forward_path interface.

Add a special case to dev_fill_forward_path() by returning 1 in case
.ndo_fill_forward_path is implemented but this is expected to be the
last device in the forward path stack.

Fixes: b5964aac51e0 ("netfilter: flowtable: consolidate xmit path")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
v2: do not incremental stack->num_path, use the existing empty slot.

 net/core/dev.c       | 4 +++-
 net/mac80211/iface.c | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index ecfbd72d5d1a..53140edfd1b4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -787,6 +787,8 @@ int dev_fill_forward_path(struct net_device_path_ctx *ctx,
 		ret = ctx->dev->netdev_ops->ndo_fill_forward_path(ctx, path);
 		if (ret < 0)
 			goto err_out;
+		else if (ret > 0)
+			goto out;
 
 		stack->num_paths++;
 		if (WARN_ON_ONCE(last_dev == ctx->dev))
@@ -795,7 +797,7 @@ int dev_fill_forward_path(struct net_device_path_ctx *ctx,
 
 	if (!ctx->dev)
 		return ret;
-
+out:
 	path = dev_fwd_path(stack);
 	if (!path)
 		goto err_out;
diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 43460a705a6b..8c0cc2b4c6ed 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -998,7 +998,7 @@ static int ieee80211_netdev_fill_forward_path(struct net_device_path_ctx *ctx,
 	local = sdata->local;
 
 	if (!local->ops->net_fill_forward_path)
-		return -EOPNOTSUPP;
+		return 1;
 
 	rcu_read_lock();
 	switch (sdata->vif.type) {
-- 
2.47.3