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From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>, passt-dev@passt.top
Subject: Re: [PATCH v3 16/16] udp: Correct splice forwarding when receiving from multiple sources
Date: Tue, 29 Nov 2022 16:59:33 +1100	[thread overview]
Message-ID: <Y4WfxX3Vdfli6icG@yekko> (raw)
In-Reply-To: <20221125072916.3060938-17-david@gibson.dropbear.id.au>

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On Fri, Nov 25, 2022 at 06:29:16PM +1100, David Gibson wrote:
> udp_sock_handler_splice() reads a whole batch of datagrams at once with
> recvmmsg().  It then forwards them all via a single socket on the other
> side, based on the source port.
> 
> However, it's entirely possible that the datagrams in the set have
> different source ports, and thus ought to be forwarded via different
> sockets on the destination side.  In fact this situation arises with the
> iperf -P4 throughput tests in our own test suite.  AFAICT we only get away
> with this because iperf3 is strictly one way and doesn't send reply packets
> which would be misdirected because of the incorrect source ports.
> 
> Alter udp_sock_handler_splice() to split the packets it receives into
> batches with the same source address and send each batch with a separate
> sendmmsg().
> 
> For now we only look for already contiguous batches, which means that if
> there are multiple active flows interleaved this is likely to degenerate
> to batches of size 1.  For now this is the simplest way to correct the
> behaviour and we can try to optimize later.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

Oops, replied to the wrong version.  v3 still has the nasty bug, do
not apply until I send a v4.

> ---
>  udp.c | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/udp.c b/udp.c
> index 899dcbb..eaf7a52 100644
> --- a/udp.c
> +++ b/udp.c
> @@ -571,9 +571,9 @@ static void udp_splice_sendfrom(const struct ctx *c, struct mmsghdr *mmh, int n,
>  static void udp_sock_handler_splice(const struct ctx *c, union epoll_ref ref,
>  				    uint32_t events, const struct timespec *now)
>  {
> -	in_port_t src, dst = ref.r.p.udp.udp.port;
> +	in_port_t dst = ref.r.p.udp.udp.port;
> +	int v6 = ref.r.p.udp.udp.v6, n, i, m;
>  	struct mmsghdr *mmh_recv, *mmh_send;
> -	int v6 = ref.r.p.udp.udp.v6, n, i;
>  
>  	if (!(events & EPOLLIN))
>  		return;
> @@ -609,12 +609,23 @@ static void udp_sock_handler_splice(const struct ctx *c, union epoll_ref ref,
>  		});
>  	}
>  
> -	for (i = 0; i < n; i++)
> -		mmh_send[i].msg_hdr.msg_iov->iov_len = mmh_recv[i].msg_len;
> -
> -	src = sa_port(v6, mmh_recv[0].msg_hdr.msg_name);
> -	udp_splice_sendfrom(c, mmh_send, n, src, ref.r.p.udp.udp.port,
> -			    v6, ref.r.p.udp.udp.ns, ref.r.p.udp.udp.orig, now);
> +	for (i = 0; i < n; i += m) {
> +		const struct mmsghdr *mmh = &mmh_recv[i];
> +		in_port_t src = sa_port(v6, mmh->msg_hdr.msg_name);
> +
> +		m = 0;
> +		do {
> +			mmh_send[i + m].msg_hdr.msg_iov->iov_len = mmh->msg_len;
> +			mmh++;
> +			m++;
> +		} while (sa_port(v6, mmh->msg_hdr.msg_name) == src);

Buffer overflow here, because I didn't check i + m against n.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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      reply	other threads:[~2022-11-29  5:59 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-25  7:29 [PATCH v3 00/16] Simplify and correct handling of "spliced" UDP forwarding David Gibson
2022-11-25  7:29 ` [PATCH v3 01/16] udp: Also bind() connected ports for "splice" forwarding David Gibson
2022-11-25  7:29 ` [PATCH v3 02/16] udp: Separate tracking of inbound and outbound packet flows David Gibson
2022-11-25  7:29 ` [PATCH v3 03/16] udp: Always use sendto() rather than send() for forwarding spliced packets David Gibson
2022-11-25  7:29 ` [PATCH v3 04/16] udp: Don't connect "forward" sockets for spliced flows David Gibson
2022-11-25  7:29 ` [PATCH v3 05/16] udp: Remove the @bound field from union udp_epoll_ref David Gibson
2022-11-25  7:29 ` [PATCH v3 06/16] udp: Split splice field in udp_epoll_ref into (mostly) independent bits David Gibson
2022-11-25  7:29 ` [PATCH v3 07/16] udp: Don't create double sockets for -U port David Gibson
2022-11-25  7:29 ` [PATCH v3 08/16] udp: Re-use fixed bound sockets for packet forwarding when possible David Gibson
2022-11-25  7:29 ` [PATCH v3 09/16] udp: Don't explicitly track originating socket for spliced "connections" David Gibson
2022-11-25  7:29 ` [PATCH v3 10/16] udp: Update UDP "connection" timestamps in both directions David Gibson
2022-11-25  7:29 ` [PATCH v3 11/16] udp: Simplify udp_sock_handler_splice David Gibson
2022-11-25  7:29 ` [PATCH v3 12/16] udp: Make UDP_SPLICE_FRAMES and UDP_TAP_FRAMES_MEM the same thing David Gibson
2022-11-25  7:29 ` [PATCH v3 13/16] udp: Add helper to extract port from a sockaddr_in or sockaddr_in6 David Gibson
2022-11-25  7:29 ` [PATCH v3 14/16] udp: Unify buffers for tap and splice paths David Gibson
2022-11-25  7:29 ` [PATCH v3 15/16] udp: Split send half of udp_sock_handler_splice() from the receive half David Gibson
2022-11-25  7:29 ` [PATCH v3 16/16] udp: Correct splice forwarding when receiving from multiple sources David Gibson
2022-11-29  5:59   ` David Gibson [this message]

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