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

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Date:   Mon, 19 Oct 2020 01:09:15 +0000
From:   "zhudi (J)" <zhudi21@...wei.com>
To:     Michal Kubecek <mkubecek@...e.cz>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Chenxiang (EulerOS)" <rose.chen@...wei.com>
Subject: Re: [PATCH] rtnetlink: fix data overflow in rtnl_calcit()

 > 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.

Thanks for your replying,  it's right. The patch only fix the situation that IFLA_VFINFO_LIST itself
fits into 64KB but the whole netlink message would not.