netdev - Re: [PATCH] rtnetlink: fix data overflow in rtnl

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Message-ID: <20201018114136.5f02a826@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sun, 18 Oct 2020 11:41:36 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     zhudi <zhudi21@...wei.com>, davem@...emloft.net,
        netdev@...r.kernel.org, rose.chen@...wei.com
Subject: Re: [PATCH] rtnetlink: fix data overflow in rtnl_calcit()

On Sat, 17 Oct 2020 14:34:11 +0200 Michal Kubecek wrote:
> On Fri, Oct 16, 2020 at 10:02:38AM +0800, zhudi wrote:
> > "ip addr show" command execute error when we have a physical
> > network card with number of VFs larger than 247.
> > 
> > The return value of if_nlmsg_size() in rtnl_calcit() will exceed
> > range of u16 data type when any network cards has a larger number of
> > VFs. rtnl_vfinfo_size() will significant increase needed dump size when
> > the value of num_vfs is larger.
> > 
> > Eventually we get a wrong value of min_ifinfo_dump_size because of overflow
> > which decides the memory size needed by netlink dump and netlink_dump()
> > will return -EMSGSIZE because of not enough memory was allocated.
> > 
> > So fix it by promoting  min_dump_alloc data type to u32 to
> > avoid data overflow and it's also align with the data type of
> > struct netlink_callback{}.min_dump_alloc which is assigned by
> > return value of rtnl_calcit()  
> 
> Unfortunately this is only part of the problem. For a NIC with so many
> VFs (not sure if exactly 247 but it's close to that), IFLA_VFINFO_LIST
> nested attribute itself would be over 64KB long which is not possible as
> attribute size is u16.
> 
> So we should rather fail in such case (except when IFLA_VFINFO_LIST
> itself fits into 64KB but the whole netlink message would not) and
> provide an alternative way to get information about all VFs.

Right, we should probably move to devlink as much as possible.

zhudi, why not use size_t? Seems like the most natural fit for 
counting size.