netdev - RE: [PATCH bpf-next] net: Use skb->len to check the validity of the parameters in bpf_skb_load

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Message-ID: <623160c966680_94df20819@john.notmuch>
Date:   Tue, 15 Mar 2022 21:00:09 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     "liujian (CE)" <liujian56@...wei.com>,
        Martin KaFai Lau <kafai@...com>
Cc:     "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "andrii@...nel.org" <andrii@...nel.org>,
        "songliubraving@...com" <songliubraving@...com>,
        "yhs@...com" <yhs@...com>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "kpsingh@...nel.org" <kpsingh@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "sdf@...gle.com" <sdf@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: RE: [PATCH bpf-next] net: Use skb->len to check the validity of the
 parameters in bpf_skb_load_bytes

liujian (CE) wrote:
> 
> 
> > -----Original Message-----
> > From: Martin KaFai Lau [mailto:kafai@...com]
> > Sent: Wednesday, March 16, 2022 3:58 AM
> > To: liujian (CE) <liujian56@...wei.com>
> > Cc: ast@...nel.org; daniel@...earbox.net; andrii@...nel.org;
> > songliubraving@...com; yhs@...com; john.fastabend@...il.com;
> > kpsingh@...nel.org; davem@...emloft.net; kuba@...nel.org;
> > sdf@...gle.com; netdev@...r.kernel.org; bpf@...r.kernel.org
> > Subject: Re: [PATCH bpf-next] net: Use skb->len to check the validity of the
> > parameters in bpf_skb_load_bytes
> > 
> > On Tue, Mar 15, 2022 at 08:39:16PM +0800, Liu Jian wrote:
> > > The data length of skb frags + frag_list may be greater than 0xffff,
> > > so here use skb->len to check the validity of the parameters.
> > What is the use case that needs to look beyond 0xffff ?

> I use sockmap with strparser, the stm->strp.offset (the begin of one
> application layer protocol message) maybe beyond 0xffff, but i need
> load the message head to do something.

This would explain skb_load_bytes but not the other two right? Also
if we are doing this why not just remove those two checks in
flow_dissector_load() I think skb_header_pointer() does duplicate
checks. Please check.