Linux Ethernet Bridging - Oct 2021 - [Bridge] [PATCH net] net: bridge: fix uninitialized variables when BRIDGE_CFM is disabled

Function br_get_link_af_size_filtered() calls br_cfm_{,peer}_mep_count()
but does not check their return value. When BRIDGE_CFM is not enabled
these functions return -EOPNOTSUPP but do not modify count parameter.
Calling function then works with uninitialized variables.

Fixes: b6d0425b816e ("bridge: cfm: Netlink Notifications.")
Signed-off-by: Ivan Vecera <ivecera at redhat.com>
---
 net/bridge/br_netlink.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index 5c6c4305ed23..12d602495ea0 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -126,8 +126,10 @@ static size_t br_get_link_af_size_filtered(const struct
net_device *dev,
 		return vinfo_sz;
 
 	/* CFM status info must be added */
-	br_cfm_mep_count(br, &num_cfm_mep_infos);
-	br_cfm_peer_mep_count(br, &num_cfm_peer_mep_infos);
+	if (br_cfm_mep_count(br, &num_cfm_mep_infos) < 0)
+		num_cfm_mep_infos = 0;
+	if (br_cfm_peer_mep_count(br, &num_cfm_peer_mep_infos) < 0)
+		num_cfm_peer_mep_infos = 0;
 
 	vinfo_sz += nla_total_size(0);	/* IFLA_BRIDGE_CFM */
 	/* For each status struct the MEP instance (u32) is added */
-- 
2.32.0

On 27/10/2021 16:49, Ivan Vecera wrote:
> Function br_get_link_af_size_filtered() calls br_cfm_{,peer}_mep_count()
> but does not check their return value. When BRIDGE_CFM is not enabled
> these functions return -EOPNOTSUPP but do not modify count parameter.
> Calling function then works with uninitialized variables.
> 
> Fixes: b6d0425b816e ("bridge: cfm: Netlink Notifications.")
> Signed-off-by: Ivan Vecera <ivecera at redhat.com>
> ---
>  net/bridge/br_netlink.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
> index 5c6c4305ed23..12d602495ea0 100644
> --- a/net/bridge/br_netlink.c
> +++ b/net/bridge/br_netlink.c
> @@ -126,8 +126,10 @@ static size_t br_get_link_af_size_filtered(const
struct net_device *dev,
>  		return vinfo_sz;
>  
>  	/* CFM status info must be added */
> -	br_cfm_mep_count(br, &num_cfm_mep_infos);
> -	br_cfm_peer_mep_count(br, &num_cfm_peer_mep_infos);
> +	if (br_cfm_mep_count(br, &num_cfm_mep_infos) < 0)
> +		num_cfm_mep_infos = 0;
> +	if (br_cfm_peer_mep_count(br, &num_cfm_peer_mep_infos) < 0)
> +		num_cfm_peer_mep_infos = 0;
>  
>  	vinfo_sz += nla_total_size(0);	/* IFLA_BRIDGE_CFM */
>  	/* For each status struct the MEP instance (u32) is added */
> 
Hi,
Could you please rather update the EOPNOTSUPP helpers to set these infos to 0
before
returning? Someone else might decide to use them and hit the same bug.

E.g.
static inline int br_cfm_mep_count(struct net_bridge *br, u32 *count)
{
	*count = 0;
        return -EOPNOTSUPP;
}

We already do the same for br_allowed_ingress, nbp_vlan_add() etc.

Thanks,
 Nik