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

["liujian (CE)" <liujian56@huawei.com>]

> -----Original Message-----
> From: John Fastabend [mailto:john.fastabend@gmail.com]
> Sent: Wednesday, March 16, 2022 12:00 PM
> To: liujian (CE) <liujian56@huawei.com>; Martin KaFai Lau <kafai@fb.com>
> Cc: ast@kernel.org; daniel@iogearbox.net; andrii@kernel.org;
> songliubraving@fb.com; yhs@fb.com; john.fastabend@gmail.com;
> kpsingh@kernel.org; davem@davemloft.net; kuba@kernel.org;
> sdf@google.com; netdev@vger.kernel.org; bpf@vger.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@fb.com]
> > > Sent: Wednesday, March 16, 2022 3:58 AM
> > > To: liujian (CE) <liujian56@huawei.com>
> > > Cc: ast@kernel.org; daniel@iogearbox.net; andrii@kernel.org;
> > > songliubraving@fb.com; yhs@fb.com; john.fastabend@gmail.com;
> > > kpsingh@kernel.org; davem@davemloft.net; kuba@kernel.org;
> > > sdf@google.com; netdev@vger.kernel.org; bpf@vger.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
Yes, I just see that these two functions have the same judgment.
> are doing this why not just remove those two checks in
> flow_dissector_load() I think skb_header_pointer() does duplicate checks.
> Please check.
Yes, skb_header_pointer() have checked as below, and I will send v2 to remove 0xffff check.
----skb_header_pointer
-------- __skb_header_pointer
------------skb_copy_bits
---------------- if (offset > (int)skb->len - len)
--------------------goto fault;

Thank you~