bridge: range check STP parameters

Apply restrictions on STP parameters based 802.1D 1998 standard.
   * Fixes missing locking in set path cost ioctl
   * Uses common code for both ioctl and sysfs

This is based on an earlier patch Sasikanth V but with overhaul.

Note:
1. It does NOT enforce the restriction on the relationship max_age and
   forward delay or hello time because in existing implementation these are
   set as independant operations.

2. If STP is disabled, there is no restriction on forward delay

3. No restriction on holding time because users use Linux code to act
   as hub or be sticky.

4. Although standard allow 0-255, Linux only allows 0-63 for port priority
   because more bits are reserved for port number.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 4 deletions

diff --git a/net/bridge/br_stp_if.c b/net/bridge/br_stp_if.c
index 9b61d09de9b9..6f615b8192f4 100644
--- a/net/bridge/br_stp_if.c
+++ b/net/bridge/br_stp_if.c
@@ -20,7 +20,7 @@
 
 
 /* Port id is composed of priority and port number.
- * NB: least significant bits of priority are dropped to
+ * NB: some bits of priority are dropped to
  *     make room for more ports.
  */
 static inline port_id br_make_port_id(__u8 priority, __u16 port_no)
@@ -29,6 +29,8 @@ static inline port_id br_make_port_id(__u8 priority, __u16 port_no)
 		| (port_no & ((1<<BR_PORT_BITS)-1));
 }
 
+#define BR_MAX_PORT_PRIORITY ((u16)~0 >> BR_PORT_BITS)
+
 /* called under bridge lock */
 void br_init_port(struct net_bridge_port *p)
 {
@@ -255,10 +257,14 @@ void br_stp_set_bridge_priority(struct net_bridge *br, u16 newprio)
 }
 
 /* called under bridge lock */
-void br_stp_set_port_priority(struct net_bridge_port *p, u8 newprio)
+int br_stp_set_port_priority(struct net_bridge_port *p, unsigned long newprio)
 {
-	port_id new_port_id = br_make_port_id(newprio, p->port_no);
+	port_id new_port_id;
+
+	if (newprio > BR_MAX_PORT_PRIORITY)
+		return -ERANGE;
 
+	new_port_id = br_make_port_id(newprio, p->port_no);
 	if (br_is_designated_port(p))
 		p->designated_port = new_port_id;
 
@@ -269,14 +275,21 @@ void br_stp_set_port_priority(struct net_bridge_port *p, u8 newprio)
 		br_become_designated_port(p);
 		br_port_state_selection(p->br);
 	}
+
+	return 0;
 }
 
 /* called under bridge lock */
-void br_stp_set_path_cost(struct net_bridge_port *p, u32 path_cost)
+int br_stp_set_path_cost(struct net_bridge_port *p, unsigned long path_cost)
 {
+	if (path_cost < BR_MIN_PATH_COST ||
+	    path_cost > BR_MAX_PATH_COST)
+		return -ERANGE;
+
 	p->path_cost = path_cost;
 	br_configuration_update(p->br);
 	br_port_state_selection(p->br);
+	return 0;
 }
 
 ssize_t br_show_bridge_id(char *buf, const struct bridge_id *id)