Re: [PATCH v1] rtnetlink: let rtnl_bridge_setlink checks IFLA_BRIDGE_MODE length

[Hangbin Liu]

On Tue, Jul 25, 2023 at 10:21:51AM +0800, Lin Ma wrote:
> There are totally 9 ndo_bridge_setlink handlers in the current kernel,
> which are 1) bnxt_bridge_setlink, 2) be_ndo_bridge_setlink 3)
> i40e_ndo_bridge_setlink 4) ice_bridge_setlink 5)
> ixgbe_ndo_bridge_setlink 6) mlx5e_bridge_setlink 7)
> nfp_net_bridge_setlink 8) qeth_l2_bridge_setlink 9) br_setlink.
> 
> By investigating the code, we find that 1-7 parse and use nlattr
> IFLA_BRIDGE_MODE but 3 and 4 forget to do the nla_len check. This can
> lead to an out-of-attribute read and allow a malformed nlattr (e.g.,
> length 0) to be viewed as a 2 byte integer.
> 
> To avoid such issues, also for other ndo_bridge_setlink handlers in the
> future. This patch adds the nla_len check in rtnl_bridge_setlink and
> does an early error return if length mismatches.
> 
> Fixes: b1edc14a3fbf ("ice: Implement ice_bridge_getlink and ice_bridge_setlink")
> Fixes: 51616018dd1b ("i40e: Add support for getlink, setlink ndo ops")
> Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx>
> Signed-off-by: Lin Ma <linma@xxxxxxxxxx>
> ---
>  net/core/rtnetlink.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 3ad4e030846d..1e51291007ea 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -5148,6 +5148,11 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
>  				flags = nla_get_u16(attr);
>  				break;
>  			}

If we got attr tIFLA_BRIDGE_FLAGS first, it will break here and not check
the later IFLA_BRIDGE_MODE.

> +
> +			if (nla_type(attr) == IFLA_BRIDGE_MODE) {
> +				if (nla_len(attr) < sizeof(u16))
> +					return -EINVAL;
> +			}
>  		}
>  	}

Thanks
Hangbin