Re: [bpf-next PATCH 2/3] bpf: fix running sk_skb program types with ktls

[John Fastabend <john.fastabend@gmail.com>]

Jakub Sitnicki wrote:
> On Fri, 29 May 2020 16:06:59 -0700
> John Fastabend <john.fastabend@gmail.com> wrote:
> 
> > KTLS uses a stream parser to collect TLS messages and send them to
> > the upper layer tls receive handler. This ensures the tls receiver
> > has a full TLS header to parse when it is run. However, when a
> > socket has BPF_SK_SKB_STREAM_VERDICT program attached before KTLS
> > is enabled we end up with two stream parsers running on the same
> > socket.
> > 
> > The result is both try to run on the same socket. First the KTLS
> > stream parser runs and calls read_sock() which will tcp_read_sock
> > which in turn calls tcp_rcv_skb(). This dequeues the skb from the
> > sk_receive_queue. When this is done KTLS code then data_ready()
> > callback which because we stacked KTLS on top of the bpf stream
> > verdict program has been replaced with sk_psock_start_strp(). This
> > will in turn kick the stream parser again and eventually do the
> > same thing KTLS did above calling into tcp_rcv_skb() and dequeuing
> > a skb from the sk_receive_queue.
> > 
> > At this point the data stream is broke. Part of the stream was
> > handled by the KTLS side some other bytes may have been handled
> > by the BPF side. Generally this results in either missing data
> > or more likely a "Bad Message" complaint from the kTLS receive
> > handler as the BPF program steals some bytes meant to be in a
> > TLS header and/or the TLS header length is no longer correct.
> > 
> > We've already broke the idealized model where we can stack ULPs
> > in any order with generic callbacks on the TX side to handle this.
> > So in this patch we do the same thing but for RX side. We add
> > a sk_psock_strp_enabled() helper so TLS can learn a BPF verdict
> > program is running and add a tls_sw_has_ctx_rx() helper so BPF
> > side can learn there is a TLS ULP on the socket.
> > 
> > Then on BPF side we omit calling our stream parser to avoid
> > breaking the data stream for the KTLS receiver. Then on the
> > KTLS side we call BPF_SK_SKB_STREAM_VERDICT once the KTLS
> > receiver is done with the packet but before it posts the
> > msg to userspace. This gives us symmetry between the TX and
> > RX halfs and IMO makes it usable again. On the TX side we
> > process packets in this order BPF -> TLS -> TCP and on
> > the receive side in the reverse order TCP -> TLS -> BPF.
> > 
> > Discovered while testing OpenSSL 3.0 Alpha2.0 release.
> > 
> > Fixes: d829e9c4112b5 ("tls: convert to generic sk_msg interface")
> > Signed-off-by: John Fastabend <john.fastabend@gmail.com>
> > ---
> >  include/linux/skmsg.h |    8 ++++++++
> >  include/net/tls.h     |    9 +++++++++
> >  net/core/skmsg.c      |   43 ++++++++++++++++++++++++++++++++++++++++---
> >  net/tls/tls_sw.c      |   20 ++++++++++++++++++--
> >  4 files changed, 75 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
> > index ad31c9f..08674cd 100644
> > --- a/include/linux/skmsg.h
> > +++ b/include/linux/skmsg.h
> > @@ -437,4 +437,12 @@ static inline void psock_progs_drop(struct sk_psock_progs *progs)
> >  	psock_set_prog(&progs->skb_verdict, NULL);
> >  }
> >  
> > +int sk_psock_tls_strp_read(struct sk_psock *psock, struct sk_buff *skb);
> > +
> > +static inline bool sk_psock_strp_enabled(struct sk_psock *psock)
> > +{
> > +	if (!psock)
> > +		return false;
> > +	return psock->parser.enabled;
> > +}
> >  #endif /* _LINUX_SKMSG_H */
> > diff --git a/include/net/tls.h b/include/net/tls.h
> > index bf9eb48..b74d59b 100644
> > --- a/include/net/tls.h
> > +++ b/include/net/tls.h
> > @@ -567,6 +567,15 @@ static inline bool tls_sw_has_ctx_tx(const struct sock *sk)
> >  	return !!tls_sw_ctx_tx(ctx);
> >  }
> >  
> > +static inline bool tls_sw_has_ctx_rx(const struct sock *sk)
> > +{
> > +	struct tls_context *ctx = tls_get_ctx(sk);
> > +
> > +	if (!ctx)
> > +		return false;
> > +	return !!tls_sw_ctx_rx(ctx);
> > +}
> > +
> >  void tls_sw_write_space(struct sock *sk, struct tls_context *ctx);
> >  void tls_device_write_space(struct sock *sk, struct tls_context *ctx);
> >  
> > diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> > index 9d72f71..351afbf 100644
> > --- a/net/core/skmsg.c
> > +++ b/net/core/skmsg.c
> > @@ -7,6 +7,7 @@
> >  
> >  #include <net/sock.h>
> >  #include <net/tcp.h>
> > +#include <net/tls.h>
> >  
> >  static bool sk_msg_try_coalesce_ok(struct sk_msg *msg, int elem_first_coalesce)
> >  {
> > @@ -714,6 +715,38 @@ static void sk_psock_skb_redirect(struct sk_psock *psock, struct sk_buff *skb)
> >  	}
> >  }
> >  
> > +static void sk_psock_tls_verdict_apply(struct sk_psock *psock,
> > +				       struct sk_buff *skb, int verdict)
> > +{
> > +	switch (verdict) {
> > +	case __SK_REDIRECT:
> > +		sk_psock_skb_redirect(psock, skb);
> > +		break;
> > +	case __SK_PASS:
> > +	case __SK_DROP:
> 
> The two cases above need a "fallthrough;", right?

Correct otherwise will get the "fallthrough" patch shortly after this
lands. Thanks I'll add it.

> 
> > +	default:
> > +		break;
> > +	}
> > +}

[...]

> > diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> > index 2d399b6..61043c6 100644
> > --- a/net/tls/tls_sw.c
> > +++ b/net/tls/tls_sw.c
> > @@ -1731,6 +1731,7 @@ int tls_sw_recvmsg(struct sock *sk,
> >  	long timeo;
> >  	bool is_kvec = iov_iter_is_kvec(&msg->msg_iter);
> >  	bool is_peek = flags & MSG_PEEK;
> > +	bool bpf_strp_enabled;
> >  	int num_async = 0;
> >  
> >  	flags |= nonblock;
> > @@ -1740,6 +1741,7 @@ int tls_sw_recvmsg(struct sock *sk,
> >  
> >  	psock = sk_psock_get(sk);
> >  	lock_sock(sk);
> > +	bpf_strp_enabled = sk_psock_strp_enabled(psock);
> >  
> >  	/* Process pending decrypted records. It must be non-zero-copy */
> >  	err = process_rx_list(ctx, msg, &control, &cmsg, 0, len, false,
> > @@ -1793,11 +1795,12 @@ int tls_sw_recvmsg(struct sock *sk,
> >  
> >  		if (to_decrypt <= len && !is_kvec && !is_peek &&
> >  		    ctx->control == TLS_RECORD_TYPE_DATA &&
> > -		    prot->version != TLS_1_3_VERSION)
> > +		    prot->version != TLS_1_3_VERSION &&
> > +		    !sk_psock_strp_enabled(psock))
> 
> Is this recheck of parser state intentional? Or can we test for
> "!bpf_strp_enabled" here also?

Yes I'll fix it up to use bpf_strp_enabled. Thanks

> 
> >  			zc = true;
> >  
> >  		/* Do not use async mode if record is non-data */
> > -		if (ctx->control == TLS_RECORD_TYPE_DATA)
> > +		if (ctx->control == TLS_RECORD_TYPE_DATA && !bpf_strp_enabled)
> >  			async_capable = ctx->async_capable;
> >  		else
> >  			async_capable = false;
> > @@ -1847,6 +1850,19 @@ int tls_sw_recvmsg(struct sock *sk,
> >  			goto pick_next_record;
> >  
> >  		if (!zc) {
> > +			if (bpf_strp_enabled) {
> > +				err = sk_psock_tls_strp_read(psock, skb);
> > +				if (err != __SK_PASS) {
> > +					rxm->offset = rxm->offset + rxm->full_len;
> > +					rxm->full_len = 0;
> > +					if (err == __SK_DROP)
> > +						consume_skb(skb);
> > +					ctx->recv_pkt = NULL;
> > +					__strp_unpause(&ctx->strp);
> > +					continue;
> > +				}
> > +			}
> > +
> >  			if (rxm->full_len > len) {
> >  				retain_skb = true;
> >  				chunk = len;
> > 
>