On Sat, Feb 20, 2021 at 06:29 AM CET, Cong Wang wrote:
> From: Cong Wang <cong.wang@xxxxxxxxxxxxx>
>
> Currently TCP_SKB_CB() is hard-coded in skmsg code, it certainly
> does not work for any other non-TCP protocols. We can move them to
> skb ext, but it introduces a memory allocation on fast path.
>
> Fortunately, we only need to a word-size to store all the information,
> because the flags actually only contains 1 bit so can be just packed
> into the lowest bit of the "pointer", which is stored as unsigned
> long.
>
> Inside struct sk_buff, '_skb_refdst' can be reused because skb dst is
> no longer needed after ->sk_data_ready() so we can just drop it.
>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
> Cc: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>
> Acked-by: John Fastabend <john.fastabend@xxxxxxxxx>
> Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx>
> ---
LGTM. I have some questions (below) that would help me confirm if I
understand the changes, and what could be improved, if anything.
Acked-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
> include/linux/skbuff.h | 3 +++
> include/linux/skmsg.h | 35 +++++++++++++++++++++++++++++++++++
> include/net/tcp.h | 19 -------------------
> net/core/skmsg.c | 32 ++++++++++++++++++++------------
> net/core/sock_map.c | 8 ++------
> 5 files changed, 60 insertions(+), 37 deletions(-)
>
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 6d0a33d1c0db..bd84f799c952 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -755,6 +755,9 @@ struct sk_buff {
> void (*destructor)(struct sk_buff *skb);
> };
> struct list_head tcp_tsorted_anchor;
> +#ifdef CONFIG_NET_SOCK_MSG
> + unsigned long _sk_redir;
> +#endif
> };
>
> #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
> diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
> index e3bb712af257..fc234d507fd7 100644
> --- a/include/linux/skmsg.h
> +++ b/include/linux/skmsg.h
> @@ -459,4 +459,39 @@ static inline bool sk_psock_strp_enabled(struct sk_psock *psock)
> return false;
> return !!psock->saved_data_ready;
> }
> +
> +#if IS_ENABLED(CONFIG_NET_SOCK_MSG)
> +static inline bool skb_bpf_ingress(const struct sk_buff *skb)
> +{
> + unsigned long sk_redir = skb->_sk_redir;
> +
> + return sk_redir & BPF_F_INGRESS;
> +}
> +
> +static inline void skb_bpf_set_ingress(struct sk_buff *skb)
> +{
> + skb->_sk_redir |= BPF_F_INGRESS;
> +}
> +
> +static inline void skb_bpf_set_redir(struct sk_buff *skb, struct sock *sk_redir,
> + bool ingress)
> +{
> + skb->_sk_redir = (unsigned long)sk_redir;
> + if (ingress)
> + skb->_sk_redir |= BPF_F_INGRESS;
> +}
> +
> +static inline struct sock *skb_bpf_redirect_fetch(const struct sk_buff *skb)
> +{
> + unsigned long sk_redir = skb->_sk_redir;
> +
> + sk_redir &= ~0x1UL;
We're using the enum when setting the bit flag, but a hardcoded constant
when masking it. ~BPF_F_INGRESS would be more consistent here.
> + return (struct sock *)sk_redir;
> +}
> +
> +static inline void skb_bpf_redirect_clear(struct sk_buff *skb)
> +{
> + skb->_sk_redir = 0;
> +}
> +#endif /* CONFIG_NET_SOCK_MSG */
> #endif /* _LINUX_SKMSG_H */
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 947ef5da6867..075de26f449d 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -883,30 +883,11 @@ struct tcp_skb_cb {
> struct inet6_skb_parm h6;
> #endif
> } header; /* For incoming skbs */
> - struct {
> - __u32 flags;
> - struct sock *sk_redir;
> - } bpf;
> };
> };
>
> #define TCP_SKB_CB(__skb) ((struct tcp_skb_cb *)&((__skb)->cb[0]))
>
> -static inline bool tcp_skb_bpf_ingress(const struct sk_buff *skb)
> -{
> - return TCP_SKB_CB(skb)->bpf.flags & BPF_F_INGRESS;
> -}
> -
> -static inline struct sock *tcp_skb_bpf_redirect_fetch(struct sk_buff *skb)
> -{
> - return TCP_SKB_CB(skb)->bpf.sk_redir;
> -}
> -
> -static inline void tcp_skb_bpf_redirect_clear(struct sk_buff *skb)
> -{
> - TCP_SKB_CB(skb)->bpf.sk_redir = NULL;
> -}
> -
> extern const struct inet_connection_sock_af_ops ipv4_specific;
>
> #if IS_ENABLED(CONFIG_IPV6)
> diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> index 2d8bbb3fd87c..05b5af09ff42 100644
> --- a/net/core/skmsg.c
> +++ b/net/core/skmsg.c
> @@ -494,6 +494,8 @@ static int sk_psock_skb_ingress_self(struct sk_psock *psock, struct sk_buff *skb
> static int sk_psock_handle_skb(struct sk_psock *psock, struct sk_buff *skb,
> u32 off, u32 len, bool ingress)
> {
> + skb_bpf_redirect_clear(skb);
This is called to avoid leaking state in skb->_skb_refdst. Correct?
I'm wondering why we're doing it every time sk_psock_handle_skb() gets
invoked from the do/while loop in sk_psock_backlog(), instead of doing
it once after reading ingress flag with skb_bpf_ingress()?
> +
> if (!ingress) {
> if (!sock_writeable(psock->sk))
> return -EAGAIN;
> @@ -525,7 +527,7 @@ static void sk_psock_backlog(struct work_struct *work)
> len = skb->len;
> off = 0;
> start:
> - ingress = tcp_skb_bpf_ingress(skb);
> + ingress = skb_bpf_ingress(skb);
> do {
> ret = -EIO;
> if (likely(psock->sk->sk_socket))
> @@ -631,7 +633,12 @@ void __sk_psock_purge_ingress_msg(struct sk_psock *psock)
>
> static void sk_psock_zap_ingress(struct sk_psock *psock)
> {
> - __skb_queue_purge(&psock->ingress_skb);
> + struct sk_buff *skb;
> +
> + while ((skb = __skb_dequeue(&psock->ingress_skb)) != NULL) {
> + skb_bpf_redirect_clear(skb);
I believe we clone the skb before enqueuing it psock->ingress_skb.
Clone happens either in sk_psock_verdict_recv() or in __strp_recv().
There are not other users holding a ref, so clearing the redirect seems
unneeded. Unless I'm missing something?
> + kfree_skb(skb);
> + }
> __sk_psock_purge_ingress_msg(psock);
> }
>
> @@ -752,7 +759,7 @@ static void sk_psock_skb_redirect(struct sk_buff *skb)
> struct sk_psock *psock_other;
> struct sock *sk_other;
>
> - sk_other = tcp_skb_bpf_redirect_fetch(skb);
> + sk_other = skb_bpf_redirect_fetch(skb);
> /* This error is a buggy BPF program, it returned a redirect
> * return code, but then didn't set a redirect interface.
> */
> @@ -802,9 +809,10 @@ int sk_psock_tls_strp_read(struct sk_psock *psock, struct sk_buff *skb)
> * TLS context.
> */
> skb->sk = psock->sk;
> - tcp_skb_bpf_redirect_clear(skb);
> + skb_dst_drop(skb);
> + skb_bpf_redirect_clear(skb);
After skb_dst_drop(), skb->_skb_refdst is clear. So it seems the
redirect_clear() is not needed. But I'm guessing it is being invoked
to communicate the intention?
> ret = sk_psock_bpf_run(psock, prog, skb);
> - ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
> + ret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));
> skb->sk = NULL;
> }
> sk_psock_tls_verdict_apply(skb, psock->sk, ret);
> @@ -816,7 +824,6 @@ EXPORT_SYMBOL_GPL(sk_psock_tls_strp_read);
> static void sk_psock_verdict_apply(struct sk_psock *psock,
> struct sk_buff *skb, int verdict)
> {
> - struct tcp_skb_cb *tcp;
> struct sock *sk_other;
> int err = -EIO;
>
> @@ -828,8 +835,7 @@ static void sk_psock_verdict_apply(struct sk_psock *psock,
> goto out_free;
> }
>
> - tcp = TCP_SKB_CB(skb);
> - tcp->bpf.flags |= BPF_F_INGRESS;
> + skb_bpf_set_ingress(skb);
>
> /* If the queue is empty then we can submit directly
> * into the msg queue. If its not empty we have to
> @@ -890,9 +896,10 @@ static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb)
> skb_set_owner_r(skb, sk);
> prog = READ_ONCE(psock->progs.skb_verdict);
> if (likely(prog)) {
> - tcp_skb_bpf_redirect_clear(skb);
> + skb_dst_drop(skb);
> + skb_bpf_redirect_clear(skb);
> ret = sk_psock_bpf_run(psock, prog, skb);
> - ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
> + ret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));
> }
> sk_psock_verdict_apply(psock, skb, ret);
> out:
> @@ -1005,9 +1012,10 @@ static int sk_psock_verdict_recv(read_descriptor_t *desc, struct sk_buff *skb,
> skb_set_owner_r(skb, sk);
> prog = READ_ONCE(psock->progs.skb_verdict);
> if (likely(prog)) {
> - tcp_skb_bpf_redirect_clear(skb);
> + skb_dst_drop(skb);
> + skb_bpf_redirect_clear(skb);
> ret = sk_psock_bpf_run(psock, prog, skb);
> - ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb));
> + ret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));
> }
> sk_psock_verdict_apply(psock, skb, ret);
> out:
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index 1a28a5c2c61e..dbfcd7006338 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -657,7 +657,6 @@ const struct bpf_func_proto bpf_sock_map_update_proto = {
> BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
> struct bpf_map *, map, u32, key, u64, flags)
> {
> - struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
> struct sock *sk;
>
> if (unlikely(flags & ~(BPF_F_INGRESS)))
> @@ -667,8 +666,7 @@ BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
> if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
> return SK_DROP;
>
> - tcb->bpf.flags = flags;
> - tcb->bpf.sk_redir = sk;
> + skb_bpf_set_redir(skb, sk, flags & BPF_F_INGRESS);
> return SK_PASS;
> }
>
> @@ -1250,7 +1248,6 @@ const struct bpf_func_proto bpf_sock_hash_update_proto = {
> BPF_CALL_4(bpf_sk_redirect_hash, struct sk_buff *, skb,
> struct bpf_map *, map, void *, key, u64, flags)
> {
> - struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
> struct sock *sk;
>
> if (unlikely(flags & ~(BPF_F_INGRESS)))
> @@ -1260,8 +1257,7 @@ BPF_CALL_4(bpf_sk_redirect_hash, struct sk_buff *, skb,
> if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
> return SK_DROP;
>
> - tcb->bpf.flags = flags;
> - tcb->bpf.sk_redir = sk;
> + skb_bpf_set_redir(skb, sk, flags & BPF_F_INGRESS);
> return SK_PASS;
> }
