netdev - Re: [PATCH RESEND bpf 2/4] bpf, sockmap: Fix missing BPF_F_INGRESS flag when using apply

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Date:   Wed, 23 Nov 2022 14:01:24 +0800
From:   "Pengcheng Yang" <yangpc@...gsu.com>
To:     "'John Fastabend'" <john.fastabend@...il.com>,
        <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        "'Daniel Borkmann'" <daniel@...earbox.net>,
        "'Jakub Sitnicki'" <jakub@...udflare.com>,
        "'Lorenz Bauer'" <lmb@...udflare.com>
Subject: Re: [PATCH RESEND bpf 2/4] bpf, sockmap: Fix missing BPF_F_INGRESS flag when using apply_bytes

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()).