[PATCH net v2] bridge: cfm: reject invalid CCM interval at configuration time

[Xiang Mei <xmei5@asu.edu>]

ccm_tx_work_expired() re-arms itself via queue_delayed_work() using
the configured exp_interval converted by interval_to_us(). When
exp_interval is BR_CFM_CCM_INTERVAL_NONE or out of range,
interval_to_us() returns 0, causing the worker to fire immediately in
a tight loop that allocates skbs until OOM.

Fix this by validating exp_interval at configuration time:

 - Constrain IFLA_BRIDGE_CFM_CC_CONFIG_EXP_INTERVAL to [1, 7] in the
   netlink policy so userspace cannot set an invalid value.

 - Reject starting CCM TX in br_cfm_cc_ccm_tx() when exp_interval has
   not yet been configured (defaults to 0 from kzalloc).

Fixes: a806ad8ee2aa ("bridge: cfm: Kernel space implementation of CFM. CCM frame TX added.")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Xiang Mei <xmei5@asu.edu>
---
v2: Move validation out of the datapath and into configuration

 net/bridge/br_cfm.c         | 6 ++++++
 net/bridge/br_cfm_netlink.c | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/bridge/br_cfm.c b/net/bridge/br_cfm.c
index 118c7ea48c35..dea56fffa1c1 100644
--- a/net/bridge/br_cfm.c
+++ b/net/bridge/br_cfm.c
@@ -805,6 +805,12 @@ int br_cfm_cc_ccm_tx(struct net_bridge *br, const u32 instance,
 		goto save;
 	}
 
+	if (!interval_to_us(mep->cc_config.exp_interval)) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "Invalid CCM interval");
+		return -EINVAL;
+	}
+
 	/* Start delayed work to transmit CCM frames. It is done with zero delay
 	 * to send first frame immediately
 	 */
diff --git a/net/bridge/br_cfm_netlink.c b/net/bridge/br_cfm_netlink.c
index 2faab44652e7..1bb33c8f587b 100644
--- a/net/bridge/br_cfm_netlink.c
+++ b/net/bridge/br_cfm_netlink.c
@@ -34,7 +34,7 @@ br_cfm_cc_config_policy[IFLA_BRIDGE_CFM_CC_CONFIG_MAX + 1] = {
 	[IFLA_BRIDGE_CFM_CC_CONFIG_UNSPEC]	 = { .type = NLA_REJECT },
 	[IFLA_BRIDGE_CFM_CC_CONFIG_INSTANCE]	 = { .type = NLA_U32 },
 	[IFLA_BRIDGE_CFM_CC_CONFIG_ENABLE]	 = { .type = NLA_U32 },
-	[IFLA_BRIDGE_CFM_CC_CONFIG_EXP_INTERVAL] = { .type = NLA_U32 },
+	[IFLA_BRIDGE_CFM_CC_CONFIG_EXP_INTERVAL] = NLA_POLICY_RANGE(NLA_U32, 1, 7),
 	[IFLA_BRIDGE_CFM_CC_CONFIG_EXP_MAID]	 = {
 	.type = NLA_BINARY, .len = CFM_MAID_LENGTH },
 };
-- 
2.43.0