[PATCH net] net: bridge: netlink: do not clear the vlan info dump error

[Linkui Xiao <xiaolinkui@126.com>]

From: Linkui Xiao <xiaolinkui@kylinos.cn>

br_fill_ifinfo() assigns the result of br_fill_vlan_tunnel_info() over
the result of br_fill_ifvlaninfo() or br_fill_ifvlaninfo_compressed()
instead of only running the second helper when the first one succeeded.

When the vlan information no longer fits in the skb but the port has no
vlan mapped to a tunnel dst, br_fill_vlan_tunnel_info() walks the vlan
list and returns 0 without touching the skb. The -EMSGSIZE is lost,
br_fill_ifinfo() completes a message whose IFLA_AF_SPEC is truncated,
and the dump carries on to the next interface instead of stopping, so
userspace silently sees an incomplete vlan list.

Only fill the tunnel information when the vlan information was filled
successfully.

This was flagged as a pre-existing issue in the Sashiko review of the
net-next series, which noted that the VLAN fill result is overwritten
before it is tested (see the Link tag below).

Fixes: efa5356b0d97 ("bridge: per vlan dst_metadata netlink support")
Link: https://lore.kernel.org/bridge/ed1de95e-e112-4076-93f0-6f7668e657ad@blackwall.org/T/#u#5
Signed-off-by: Linkui Xiao <xiaolinkui@kylinos.cn>
---
 net/bridge/br_netlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index b2cd4e39326d..8ed86bf71a00 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -540,7 +540,7 @@ static int br_fill_ifinfo(struct sk_buff *skb,
 		else
 			err = br_fill_ifvlaninfo(skb, vg);
 
-		if (port && test_bit(BR_VLAN_TUNNEL_BIT, &port->flags))
+		if (!err && port && test_bit(BR_VLAN_TUNNEL_BIT, &port->flags))
 			err = br_fill_vlan_tunnel_info(skb, vg);
 		rcu_read_unlock();
 		if (err)
-- 
2.25.1