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: Stanislav Fomichev [mailto:sdf@google.com]
> Sent: Wednesday, March 16, 2022 11:09 PM
> To: liujian (CE) <liujian56@huawei.com>
> Cc: John Fastabend <john.fastabend@gmail.com>; Martin KaFai Lau
> <kafai@fb.com>; ast@kernel.org; daniel@iogearbox.net; andrii@kernel.org;
> songliubraving@fb.com; yhs@fb.com; kpsingh@kernel.org;
> davem@davemloft.net; kuba@kernel.org; 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 Wed, Mar 16, 2022 at 6:08 AM liujian (CE) <liujian56@huawei.com> wrote:
> >
> >
> >
> > > -----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~
> 
> Do we need to have at least "offset <= 0x7fffffff" check? IOW, do we need
> to enforce the unsignedness of the offset? Or does skb_header_pointer et
> all properly work with the negative offsets?
Yes, skb_header_pointer can not handle the negative offset.
I sent a new patch. Please help review it again. Thank you.
https://patchwork.kernel.org/project/netdevbpf/patch/20220317135940.358774-1-liujian56@huawei.com/