Subject: Re: [PATCH v2] rtnetlink: let rtnl_bridge_setlink checks IFLA_BRIDGE_MODE length

From: Hangbin Liu <[email-masked]>
Date: Tue, 25 Jul 2023 15:30:07 +0800

Hi Ma Lin,

Please add the target branch in your subject. e.g. [PATCHv2 net]

On Tue, Jul 25, 2023 at 01:57:06PM +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. To make it works, the
> break is removed from the parsing for IFLA_BRIDGE_FLAGS to make sure
> this nla_for_each_nested iterates every attribute.

Since you have checked the length in rtnl_bridge_setlink(). Can we remove
the check in the driver handlers to avoid duplicate code? You can hold on
this update and see if others have different opinion.

Thanks
Hangbin

> 
> 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 <[email-masked]>
> Signed-off-by: Lin Ma <[email-masked]>
> ---
> V1 -> V2: removes the break in parsing for IFLA_BRIDGE_FLAGS suggested
>           by Hangbin Liu <[email-masked]>
> 
>  net/core/rtnetlink.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 3ad4e030846d..aef25aa5cf1d 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -5140,13 +5140,17 @@ static int rtnl_bridge_setlink(struct sk_buff *skb, struct nlmsghdr *nlh,
>  	br_spec = nlmsg_find_attr(nlh, sizeof(struct ifinfomsg), IFLA_AF_SPEC);
>  	if (br_spec) {
>  		nla_for_each_nested(attr, br_spec, rem) {
> -			if (nla_type(attr) == IFLA_BRIDGE_FLAGS) {
> +			if (nla_type(attr) == IFLA_BRIDGE_FLAGS && !have_flags) {
>  				if (nla_len(attr) < sizeof(flags))
>  					return -EINVAL;
>  
>  				have_flags = true;
>  				flags = nla_get_u16(attr);
> -				break;
> +			}
> +
> +			if (nla_type(attr) == IFLA_BRIDGE_MODE) {
> +				if (nla_len(attr) < sizeof(u16))
> +					return -EINVAL;
>  			}
>  		}
>  	}
> -- 
> 2.17.1
>