On Wed, Jul 13, 2022 at 12:23 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
>
> On 7/13/22 3:26 AM, Joanne Koong wrote:
> > In the case where flags is 0, bpf_skb_pull_data and sk_skb_pull_data
> > should pull the entire skb payload including the bytes in the non-linear
> > page buffers.
> >
> > This is documented in the uapi:
> > "If a zero value is passed for *len*, then the whole length of the *skb*
> > is pulled"
> >
> > Fixes: 36bbef52c7eb6 ("bpf: direct packet write and access for helpers
> > for clsact progs")
> > Signed-off-by: Joanne Koong <joannelkoong@xxxxxxxxx>
>
> This is not correct. We should fix the helper doc fa15601ab31e ("bpf: add
> documentation for eBPF helpers (33-41)"). It will make the head private
> for writing (e.g. for direct packet access), but not linearize the entire
> skb, so skb_headlen is correct here.
>
Great, I'll fix up the uapi doc. I'll change it to something like: "If
a zero value is passed for *len*, then all bytes in the head of the
skb will be made readable and writable".
> > ---
> > net/core/filter.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 4ef77ec5255e..97eb15891bfc 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -1838,7 +1838,7 @@ BPF_CALL_2(bpf_skb_pull_data, struct sk_buff *, skb, u32, len)
> > * access case. By this we overcome limitations of only current
> > * headroom being accessible.
> > */
> > - return bpf_try_make_writable(skb, len ? : skb_headlen(skb));
> > + return bpf_try_make_writable(skb, len ? : skb->len);
> > }
> >
> > static const struct bpf_func_proto bpf_skb_pull_data_proto = {
> > @@ -1878,7 +1878,7 @@ BPF_CALL_2(sk_skb_pull_data, struct sk_buff *, skb, u32, len)
> > * access case. By this we overcome limitations of only current
> > * headroom being accessible.
> > */
> > - return sk_skb_try_make_writable(skb, len ? : skb_headlen(skb));
> > + return sk_skb_try_make_writable(skb, len ? : skb->len);
> > }
> >
> > static const struct bpf_func_proto sk_skb_pull_data_proto = {
> >
>
