[PATCH net] net: bridge: Reject descending VLAN tunnel ranges

[Ruoyu Wang <ruoyuw560@gmail.com>]

A pair of descending VLAN and tunnel IDs can pass the tunnel range span
check. The VLAN subtraction produces a negative int, which is converted
to unsigned when compared with the u32 tunnel ID subtraction. It can
therefore equal the wrapped tunnel ID delta.

The range loop then performs no iterations. Since the batched
notification handling added a post-loop error check, this leaves err
uninitialized and makes the request's return value unpredictable.

Reject descending VLAN ranges before comparing the spans. Valid
ascending and single-entry ranges remain unchanged, while malformed
descending ranges consistently return -EINVAL.

This issue was found by a static analysis checker and confirmed by
manual source review.

Fixes: 94339443686b ("net: bridge: notify on vlan tunnel changes done via the old api")
Signed-off-by: Ruoyu Wang <ruoyuw560@gmail.com>
---
 net/bridge/br_netlink_tunnel.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_netlink_tunnel.c b/net/bridge/br_netlink_tunnel.c
index 71a12da30004c..05f560eeb789c 100644
--- a/net/bridge/br_netlink_tunnel.c
+++ b/net/bridge/br_netlink_tunnel.c
@@ -301,7 +301,8 @@ int br_process_vlan_tunnel_info(const struct net_bridge *br,
 
 		if (!(tinfo_last->flags & BRIDGE_VLAN_INFO_RANGE_BEGIN))
 			return -EINVAL;
-		if ((tinfo_curr->vid - tinfo_last->vid) !=
+		if (tinfo_curr->vid < tinfo_last->vid ||
+		    (tinfo_curr->vid - tinfo_last->vid) !=
 		    (tinfo_curr->tunid - tinfo_last->tunid))
 			return -EINVAL;
 		t = tinfo_last->tunid;
-- 
2.51.0