Re: [PATCH net v4] bridge: cfm: reject invalid CCM interval at configuration time

On 09/06/2026 09:51, Xiang Mei wrote:
> 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 the valid range
>     [BR_CFM_CCM_INTERVAL_3_3_MS, BR_CFM_CCM_INTERVAL_10_MIN] 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: 2be665c3940d ("bridge: cfm: Netlink SET configuration Interface.")
> Reported-by: Weiming Shi <[email protected]>
> Signed-off-by: Xiang Mei <[email protected]>
> ---
> v4: remove the Suggested-by tag
> v3: Correct the fix tag and avoid use magic numbers
> v2: Move validation out of the datapath and into configuration
> 
>   net/bridge/br_cfm.c         | 6 ++++++
>   net/bridge/br_cfm_netlink.c | 4 +++-
>   2 files changed, 9 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..91b9922dc3f2 100644
> --- a/net/bridge/br_cfm_netlink.c
> +++ b/net/bridge/br_cfm_netlink.c
> @@ -34,7 +34,9 @@ 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, BR_CFM_CCM_INTERVAL_3_3_MS,
> +				 BR_CFM_CCM_INTERVAL_10_MIN),
>   	[IFLA_BRIDGE_CFM_CC_CONFIG_EXP_MAID]	 = {
>   	.type = NLA_BINARY, .len = CFM_MAID_LENGTH },
>   };

Acked-by: Nikolay Aleksandrov <[email protected]>