linux-kernel - [PATCH 3.16 040/306] ipv4: accept u8 in IP

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Date:   Wed, 15 Feb 2017 22:41:40 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Eric Dumazet" <edumazet@...gle.com>,
        "Jesper Dangaard Brouer" <brouer@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Francesco Fusco" <ffusco@...hat.com>
Subject: [PATCH 3.16 040/306] ipv4: accept u8 in IP_TOS ancillary data

3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.com>

commit e895cdce683161081e3626c4f5a5c55cb72089f8 upstream.

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 ;)

Fixes: f02db315b8d8 ("ipv4: IP_TOS and IP_TTL can be specified as ancillary data")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Francesco Fusco <ffusco@...hat.com>
Cc: Jesper Dangaard Brouer <brouer@...hat.com>
Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/ipv4/ip_sockglue.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -242,9 +242,12 @@ int ip_cmsg_send(struct net *net, struct
 			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;