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Date:   Mon, 19 Oct 2020 01:59:19 +0000
From:   "zhudi (J)" <zhudi21@...wei.com>
To:     Jakub Kicinski <kuba@...nel.org>, Michal Kubecek <mkubecek@...e.cz>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "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 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.

Thanks for your replying.
min_dump_alloc original type used is u16 and it's eventually assigned to 
struct netlink_callback{}. min_dump_alloc which data type is u32. So I just simply
promote to u32.
Should be used size_t instead of u32?

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