Subject: Re: [PATCH net-next] ipv4: accept u8 in IP_TOS ancillary data

From: Jesper Dangaard Brouer <[email-masked]>
Date: Thu, 8 Sep 2016 11:15:19 +0200

On Wed, 07 Sep 2016 21:52:56 -0700
Eric Dumazet <[email-masked]> wrote:

> From: Eric Dumazet <[email-masked]>
> 
> In commit f02db315b8d8 ("ipv4: IP_TOS and IP_TTL can be specified as
> ancillary data") Francesco added IP_TOS values specified as integer.
> 
> However, kernel sends to userspace (at recvmsg() time) an IP_TOS value
> in a single byte, when IP_RECVTOS is set on the socket.
> 
> It can be very useful to reflect all ancillary options as given by the
> kernel in a subsequent sendmsg(), instead of aborting the sendmsg() with
> EINVAL after Francesco patch.
> 
> So this patch extends IP_TOS ancillary to accept an u8, so that an UDP
> server can simply reuse same ancillary block without having to mangle
> it.
> 
> Jesper can then augment
> https://github.com/netoptimizer/network-testing/blob/master/src/udp_example02.c
> to add TOS reflection ;)

This is actually your old program ;-)
Do I need to change anything, as I'm just bouncing the packet back with sendmsg() ?

> Fixes: f02db315b8d8 ("ipv4: IP_TOS and IP_TTL can be specified as ancillary data")
> Signed-off-by: Eric Dumazet <[email-masked]>
> Cc: Francesco Fusco <[email-masked]> 
> Cc: Jesper Dangaard Brouer <[email-masked]>

Looks like a good fix,

Acked-by: Jesper Dangaard Brouer <[email-masked]>

> ---
>  net/ipv4/ip_sockglue.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
> index 71a52f4d4cffba2db9353f43dc817689bf4fab10..af4919792b6a812041dcb18ff30aa8b27482c7a2 100644
> --- a/net/ipv4/ip_sockglue.c
> +++ b/net/ipv4/ip_sockglue.c
> @@ -284,9 +284,12 @@ int ip_cmsg_send(struct sock *sk, struct msghdr *msg, struct ipcm_cookie *ipc,
>  			ipc->ttl = val;
>  			break;
>  		case IP_TOS:
> -			if (cmsg->cmsg_len != CMSG_LEN(sizeof(int)))
> +			if (cmsg->cmsg_len == CMSG_LEN(sizeof(int)))
> +				val = *(int *)CMSG_DATA(cmsg);
> +			else if (cmsg->cmsg_len == CMSG_LEN(sizeof(u8)))
> +				val = *(u8 *)CMSG_DATA(cmsg);
> +			else
>  				return -EINVAL;
> -			val = *(int *)CMSG_DATA(cmsg);
>  			if (val < 0 || val > 255)
>  				return -EINVAL;
>  			ipc->tos = val;
> 
> 

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer