On Sat, May 18, 2019 at 08:38:46AM -1000, Joe Stringer wrote:
> On Fri, May 17, 2019, 12:02 Martin Lau <kafai@xxxxxx> wrote:
>
> > On Fri, May 17, 2019 at 02:51:48PM -0700, Eric Dumazet wrote:
> > >
> > >
> > > On 5/17/19 2:21 PM, Martin KaFai Lau wrote:
> > > > The BPF_FUNC_sk_lookup_xxx helpers return RET_PTR_TO_SOCKET_OR_NULL.
> > > > Meaning a fullsock ptr and its fullsock's fields in bpf_sock can be
> > > > accessed, e.g. type, protocol, mark and priority.
> > > > Some new helper, like bpf_sk_storage_get(), also expects
> > > > ARG_PTR_TO_SOCKET is a fullsock.
> > > >
> > > > bpf_sk_lookup() currently calls sk_to_full_sk() before returning.
> > > > However, the ptr returned from sk_to_full_sk() is not guaranteed
> > > > to be a fullsock. For example, it cannot get a fullsock if sk
> > > > is in TCP_TIME_WAIT.
> > > >
> > > > This patch checks for sk_fullsock() before returning. If it is not
> > > > a fullsock, sock_gen_put() is called if needed and then returns NULL.
> > > >
> > > > Fixes: 6acc9b432e67 ("bpf: Add helper to retrieve socket in BPF")
> > > > Cc: Joe Stringer <joe@xxxxxxxxxxxxx>
> > > > Signed-off-by: Martin KaFai Lau <kafai@xxxxxx>
> > > > ---
> > > > net/core/filter.c | 16 ++++++++++++++--
> > > > 1 file changed, 14 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/net/core/filter.c b/net/core/filter.c
> > > > index 55bfc941d17a..85def5a20aaf 100644
> > > > --- a/net/core/filter.c
> > > > +++ b/net/core/filter.c
> > > > @@ -5337,8 +5337,14 @@ __bpf_sk_lookup(struct sk_buff *skb, struct
> > bpf_sock_tuple *tuple, u32 len,
> > > > struct sock *sk = __bpf_skc_lookup(skb, tuple, len, caller_net,
> > > > ifindex, proto, netns_id,
> > flags);
> > > >
> > > > - if (sk)
> > > > + if (sk) {
> > > > sk = sk_to_full_sk(sk);
> > > > + if (!sk_fullsock(sk)) {
> > > > + if (!sock_flag(sk, SOCK_RCU_FREE))
> > > > + sock_gen_put(sk);
> > >
> > > This looks a bit convoluted/weird.
> > >
> > > What about telling/asking __bpf_skc_lookup() to not return a non
> > fullsock instead ?
> > It is becausee some other helpers, like BPF_FUNC_skc_lookup_tcp,
> > can return non fullsock
> >
>
> FYI this is necessary for finding a transparently proxied socket for a
> non-local connection (tproxy use case).
You meant it is necessary to return a non fullsock from the
BPF_FUNC_sk_lookup_xxx helpers?
>
>
> > >
> > > > + return NULL;
> > > > + }
> > > > + }
> > > >
> > > > return sk;
> > > > }
> > > > @@ -5369,8 +5375,14 @@ bpf_sk_lookup(struct sk_buff *skb, struct
> > bpf_sock_tuple *tuple, u32 len,
> > > > struct sock *sk = bpf_skc_lookup(skb, tuple, len, proto, netns_id,
> > > > flags);
> > > >
> > > > - if (sk)
> > > > + if (sk) {
> > > > sk = sk_to_full_sk(sk);
> > > > + if (!sk_fullsock(sk)) {
> > > > + if (!sock_flag(sk, SOCK_RCU_FREE))
> > > > + sock_gen_put(sk);
> > > > + return NULL;
> > > > + }
> > > > + }
> > > >
> > > > return sk;
> > > > }
> > > >
> >
