netdev - Re: [PATCH bpf-next 4/4] bpf: inet_diag: Dump bpf_sk_storages in inet_diag

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Message-ID: <20200225170824.dhwkw2ojzsfz223k@kafai-mbp>
Date:   Tue, 25 Feb 2020 09:08:24 -0800
From:   Martin KaFai Lau <kafai@...com>
To:     Song Liu <song@...nel.org>
CC:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 4/4] bpf: inet_diag: Dump bpf_sk_storages in
 inet_diag_dump()

On Mon, Feb 24, 2020 at 09:47:33PM -0800, Song Liu wrote:
> On Fri, Feb 21, 2020 at 10:49 AM Martin KaFai Lau <kafai@...com> wrote:
> >
> > This patch will dump out the bpf_sk_storages of a sk
> > if the request has the INET_DIAG_REQ_SK_BPF_STORAGES nlattr.
> >
> > An array of SK_DIAG_BPF_STORAGE_REQ_MAP_FD can be specified in
> > INET_DIAG_REQ_SK_BPF_STORAGES to select which bpf_sk_storage to dump.
> > If no map_fd is specified, all bpf_sk_storages of a sk will be dumped.
> [...]
> 
> > Signed-off-by: Martin KaFai Lau <kafai@...com>
> > ---
> >  include/linux/inet_diag.h      |  4 ++
> >  include/linux/netlink.h        |  4 +-
> >  include/uapi/linux/inet_diag.h |  2 +
> >  net/ipv4/inet_diag.c           | 71 ++++++++++++++++++++++++++++++++++
> >  4 files changed, 79 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/inet_diag.h b/include/linux/inet_diag.h
> > index 1bb94cac265f..e4ba25d63913 100644
> > --- a/include/linux/inet_diag.h
> > +++ b/include/linux/inet_diag.h
> > @@ -38,9 +38,13 @@ struct inet_diag_handler {
> >         __u16           idiag_info_size;
> >  };
> >
> > +struct bpf_sk_storage_diag;
> >  struct inet_diag_dump_data {
> >         struct nlattr *req_nlas[__INET_DIAG_REQ_MAX];
> >  #define inet_diag_nla_bc req_nlas[INET_DIAG_REQ_BYTECODE]
> > +#define inet_diag_nla_bpf_stgs req_nlas[INET_DIAG_REQ_SK_BPF_STORAGES]
> > +
> > +       struct bpf_sk_storage_diag *bpf_stg_diag;
> >  };
> >
> >  struct inet_connection_sock;
> > diff --git a/include/linux/netlink.h b/include/linux/netlink.h
> > index 205fa7b1f07a..788969ccbbde 100644
> > --- a/include/linux/netlink.h
> > +++ b/include/linux/netlink.h
> > @@ -188,10 +188,10 @@ struct netlink_callback {
> >         struct module           *module;
> >         struct netlink_ext_ack  *extack;
> >         u16                     family;
> > -       u16                     min_dump_alloc;
> > -       bool                    strict_check;
> >         u16                     answer_flags;
> > +       u32                     min_dump_alloc;
> 
> Maybe highlight this change in the commit log?
ok.

> 
> >         unsigned int            prev_seq, seq;
> > +       bool                    strict_check;
> >         union {
> >                 u8              ctx[48];
> >

[ ... ]

> > diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
> > index 4bce8a477699..8ca4d54d7c5a 100644

[ ... ]

> > @@ -1022,8 +1069,11 @@ static int __inet_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
> >                             const struct inet_diag_req_v2 *r)
> >  {
> >         const struct inet_diag_handler *handler;
> > +       u32 prev_min_dump_alloc;
> >         int err = 0;
> >
> > +again:
> > +       prev_min_dump_alloc = cb->min_dump_alloc;
> >         handler = inet_diag_lock_handler(r->sdiag_protocol);
> >         if (!IS_ERR(handler))
> >                 handler->dump(skb, cb, r);
> > @@ -1031,6 +1081,12 @@ static int __inet_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
> >                 err = PTR_ERR(handler);
> >         inet_diag_unlock_handler(handler);
> >
> > +       if (!skb->len && cb->min_dump_alloc > prev_min_dump_alloc) {
> 
> Why do we check for !skb->len here?
skb contains the info of sk(s) to be dumped to the userspace.
It may contain no sk info (i.e. !skb->len),  1 sk info, 2 sk info...etc.
It only retries if there is no sk info and the cb->min_dump_alloc becomes
larger (together, it means the current skb is not large enough to fit one
sk info).

> 
> > +               err = pskb_expand_head(skb, 0, cb->min_dump_alloc, GFP_KERNEL);
> > +               if (!err)
> > +                       goto again;
> > +       }
> > +
> >         return err ? : skb->len;
> >  }
> >