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Date: Mon, 28 Nov 2022 10:18:33 -0800
From: John Fastabend <john.fastabend@...il.com>
To: Jakub Sitnicki <jakub@...udflare.com>,
Pengcheng Yang <yangpc@...gsu.com>
Cc: 'John Fastabend' <john.fastabend@...il.com>, bpf@...r.kernel.org,
netdev@...r.kernel.org, 'Daniel Borkmann' <daniel@...earbox.net>,
'Lorenz Bauer' <lmb@...udflare.com>
Subject: Re: [PATCH RESEND bpf 2/4] bpf, sockmap: Fix missing BPF_F_INGRESS
flag when using apply_bytes
Jakub Sitnicki wrote:
> On Wed, Nov 23, 2022 at 02:01 PM +08, Pengcheng Yang wrote:
> > John Fastabend <john.fastabend@...il.com> wrote:
> >>
> >> Pengcheng Yang wrote:
> >> > When redirecting, we use sk_msg_to_ingress() to get the BPF_F_INGRESS
> >> > flag from the msg->flags. If apply_bytes is used and it is larger than
> >> > the current data being processed, sk_psock_msg_verdict() will not be
> >> > called when sendmsg() is called again. At this time, the msg->flags is 0,
> >> > and we lost the BPF_F_INGRESS flag.
> >> >
> >> > So we need to save the BPF_F_INGRESS flag in sk_psock and assign it to
> >> > msg->flags before redirection.
> >> >
> >> > Fixes: 8934ce2fd081 ("bpf: sockmap redirect ingress support")
> >> > Signed-off-by: Pengcheng Yang <yangpc@...gsu.com>
> >> > ---
> >> > include/linux/skmsg.h | 1 +
> >> > net/core/skmsg.c | 1 +
> >> > net/ipv4/tcp_bpf.c | 1 +
> >> > net/tls/tls_sw.c | 1 +
> >> > 4 files changed, 4 insertions(+)
> >> >
> >> > diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
> >> > index 48f4b64..e1d463f 100644
> >> > --- a/include/linux/skmsg.h
> >> > +++ b/include/linux/skmsg.h
> >> > @@ -82,6 +82,7 @@ struct sk_psock {
> >> > u32 apply_bytes;
> >> > u32 cork_bytes;
> >> > u32 eval;
> >> > + u32 flags;
> >> > struct sk_msg *cork;
> >> > struct sk_psock_progs progs;
> >> > #if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)
> >> > diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> >> > index 188f855..ab2f8f3 100644
> >> > --- a/net/core/skmsg.c
> >> > +++ b/net/core/skmsg.c
> >> > @@ -888,6 +888,7 @@ int sk_psock_msg_verdict(struct sock *sk, struct sk_psock *psock,
> >> > if (psock->sk_redir)
> >> > sock_put(psock->sk_redir);
> >> > psock->sk_redir = msg->sk_redir;
> >> > + psock->flags = msg->flags;
> >> > if (!psock->sk_redir) {
> >> > ret = __SK_DROP;
> >> > goto out;
> >> > diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> >> > index ef5de4f..1390d72 100644
> >> > --- a/net/ipv4/tcp_bpf.c
> >> > +++ b/net/ipv4/tcp_bpf.c
> >> > @@ -323,6 +323,7 @@ static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock,
> >> > break;
> >> > case __SK_REDIRECT:
> >> > sk_redir = psock->sk_redir;
> >> > + msg->flags = psock->flags;
> >> > sk_msg_apply_bytes(psock, tosend);
> >> > if (!psock->apply_bytes) {
> >> > /* Clean up before releasing the sock lock. */
> >> ^^^^^^^^^^^^^^^
> >> In this block reposted here with the rest of the block
> >>
> >>
> >> if (!psock->apply_bytes) {
> >> /* Clean up before releasing the sock lock. */
> >> eval = psock->eval;
> >> psock->eval = __SK_NONE;
> >> psock->sk_redir = NULL;
> >> }
> >>
> >> Now that we have a psock->flags we should clera that as
> >> well right?
> >
> > According to my understanding, it is not necessary (but can) to clear
> > psock->flags here, because psock->flags will be overwritten by msg->flags
> > at the beginning of each redirection (in sk_psock_msg_verdict()).
>
> 1. We should at least document that psock->flags value can be garbage
> (undefined) if psock->sk_redir is null.
Per v2 I think we should not have garbage flags. Just zero the flags
field no point in saving a single insn here IMO.
>
> 2. 'flags' is amiguous (flags for what?). I'd suggest to rename to
> something like redir_flags.
>
> Also, since we don't care about all flags, but just the ingress bit,
> we should store just that. It's not about size. Less state passed
> around is easier to reason about. See patch below.
rename makes sense to me.
>
> 3. Alternatively, I'd turn psock->sk_redir into a tagged pointer, like
> skb->_sk_redir is. This way all state (pointer & flags) is bundled
> and managed together. It would be a bigger change. Would have to be
> split out from this patch set.
>
> --8<--
>
> diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
> index 70d6cb94e580..84f787416a54 100644
> --- a/include/linux/skmsg.h
> +++ b/include/linux/skmsg.h
> @@ -82,6 +82,7 @@ struct sk_psock {
> u32 apply_bytes;
> u32 cork_bytes;
> u32 eval;
> + bool redir_ingress; /* undefined if sk_redir is null */
> struct sk_msg *cork;
> struct sk_psock_progs progs;
> #if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 14d45661a84d..5b70b241ce71 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -2291,8 +2291,8 @@ int tcp_bpf_update_proto(struct sock *sk, struct sk_psock *psock, bool restore);
> void tcp_bpf_clone(const struct sock *sk, struct sock *newsk);
> #endif /* CONFIG_BPF_SYSCALL */
>
> -int tcp_bpf_sendmsg_redir(struct sock *sk, struct sk_msg *msg, u32 bytes,
> - int flags);
> +int tcp_bpf_sendmsg_redir(struct sock *sk, bool ingress,
> + struct sk_msg *msg, u32 bytes, int flags);
> #endif /* CONFIG_NET_SOCK_MSG */
>
> #if !defined(CONFIG_BPF_SYSCALL) || !defined(CONFIG_NET_SOCK_MSG)
> diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> index e6b9ced3eda8..53d0251788aa 100644
> --- a/net/core/skmsg.c
> +++ b/net/core/skmsg.c
> @@ -886,13 +886,16 @@ int sk_psock_msg_verdict(struct sock *sk, struct sk_psock *psock,
> ret = sk_psock_map_verd(ret, msg->sk_redir);
> psock->apply_bytes = msg->apply_bytes;
> if (ret == __SK_REDIRECT) {
> - if (psock->sk_redir)
> + if (psock->sk_redir) {
> sock_put(psock->sk_redir);
> - psock->sk_redir = msg->sk_redir;
> - if (!psock->sk_redir) {
> + psock->sk_redir = NULL;
> + }
> + if (!msg->sk_redir) {
> ret = __SK_DROP;
> goto out;
> }
> + psock->redir_ingress = sk_msg_to_ingress(msg);
> + psock->sk_redir = msg->sk_redir;
> sock_hold(psock->sk_redir);
> }
> out:
> diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> index cf9c3e8f7ccb..490b359dc814 100644
> --- a/net/ipv4/tcp_bpf.c
> +++ b/net/ipv4/tcp_bpf.c
> @@ -131,10 +131,9 @@ static int tcp_bpf_push_locked(struct sock *sk, struct sk_msg *msg,
> return ret;
> }
>
> -int tcp_bpf_sendmsg_redir(struct sock *sk, struct sk_msg *msg,
> - u32 bytes, int flags)
> +int tcp_bpf_sendmsg_redir(struct sock *sk, bool ingress,
> + struct sk_msg *msg, u32 bytes, int flags)
> {
> - bool ingress = sk_msg_to_ingress(msg);
> struct sk_psock *psock = sk_psock_get(sk);
> int ret;
>
> @@ -337,7 +336,8 @@ static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock,
> release_sock(sk);
>
> origsize = msg->sg.size;
> - ret = tcp_bpf_sendmsg_redir(sk_redir, msg, tosend, flags);
> + ret = tcp_bpf_sendmsg_redir(sk_redir, psock->redir_ingress,
> + msg, tosend, flags);
> sent = origsize - msg->sg.size;
>
> if (eval == __SK_REDIRECT)
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> index 264cf367e265..b22d97610b9a 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -846,7 +846,8 @@ static int bpf_exec_tx_verdict(struct sk_msg *msg, struct sock *sk,
> sk_msg_return_zero(sk, msg, send);
> msg->sg.size -= send;
> release_sock(sk);
> - err = tcp_bpf_sendmsg_redir(sk_redir, &msg_redir, send, flags);
> + err = tcp_bpf_sendmsg_redir(sk_redir, psock->redir_ingress,
> + &msg_redir, send, flags);
> lock_sock(sk);
> if (err < 0) {
> *copied -= sk_msg_free_nocharge(sk, &msg_redir);
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