Re: [PATCH v1] RDMA/nldev: Add length check for IFLA_BOND_ARP_IP_TARGET parsing

[Leon Romanovsky]

On Tue, Jul 25, 2023 at 08:11:58AM +0800, Lin Ma wrote:
> Hello Leon,
> 
> > 
> > On Sun, Jul 23, 2023 at 03:45:04PM +0800, Lin Ma wrote:
> > > The nla_for_each_nested parsing in function
> > > nldev_stat_set_counter_dynamic_doit() does not check the length of the
> > > attribute. This can lead to an out-of-attribute read and allow a
> > > malformed nlattr (e.g., length 0) to be viewed as a 4 byte integer.
> > 
> > 1. Subject of this patch doesn't really match the change.
> 
> My bad, a stupid mistake. I will fix that and prepare another patch.
> 
> > 2. See my comment on your i40e patch.
> > https://lore.kernel.org/netdev/20230724174435.GA11388@unreal/
> > 
> 
> Yeah I have seen that. Just as Jakub said, empty netlink attributes are valid 
> (they are viewed as flag). The point is that different attribute has different
> length requirement. For this specific code, the RDMA_NLDEV_ATTR_STAT_HWCOUNTERS
> attribute is a nested one whose inner attributes should be NLA_U32. But as you
> can see in variable nldev_policy, the description does not use nested policy to
> enfore that, which results in the bug discussed in my commit message.
> 
>  [RDMA_NLDEV_ATTR_STAT_HWCOUNTERS]       = { .type = NLA_NESTED },
> 
> The elegant fix could be add the nested policy description to nldev_policy while
> this is toublesome as no existing nla_attr has been given to this nested nlattr.
> Hence, add the length check is the simplest solution and you can see such nla_len
> check code all over the kernel.

Right, and this is what bothers me.

I would more than happy to change nla_for_each_nested() to be something
like nla_for_each_nested_type(...., sizeof(u32)), which will skip empty
lines, for code which can't have them.

Thanks

> 
> > Thanks
> 
> Regards
> Lin