Re: [PATCH v2] IPv6: fix bug when specifying the non-exist outgoing interface

[Brian Haley <brian.haley@hp.com>]

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Shan Wei wrote:
>   When specifying the outgoing interface with sendmsg, if the ipi6_addr is 
> the unspecified address and the ipi6_ifindex is the not-exist interface, 
> it should be fail and the errno should be set ENODEV.
>   Actually, it does well(sendmsg returns on success ), because the kernel 
> don't check the interface。

This patch changes this code path to be different than most others that 
completely ignore the device for the unspecified address - for example 
inet6_bind() and rawv6_bind().  Those paths only care about the device 
for a link-local address, so I don't think this patch is correct.

In the current git tree, this :: address is going to turn-into ::1, so 
the ifindex is irrelevant, the packet will be looped-back.  Older 
kernels could transmit the packet on the wire using the default route. 
Can you elaborate on the problem you were seeing?

I did notice a slight problem where if fl->oif is set in the caller (for 
example via SO_BINDTODEVICE), it's ignored in datagram_send_ctl() if 
src_info->ipi6_ifindex is zero, attached patch fixes that.

-Brian

Signed-off-by: Brian Haley <brian.haley@hp.com>
---

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diff --git a/net/ipv6/datagram.c b/net/ipv6/datagram.c
index 94fa6ae..b6a7c7b 100644
--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -541,7 +541,7 @@ int datagram_send_ctl(struct msghdr *msg, struct flowi *fl,
 				break;
 
 			if (addr_type & IPV6_ADDR_LINKLOCAL) {
-				if (!src_info->ipi6_ifindex)
+				if (!fl->oif)
 					return -EINVAL;
 				else {
 					dev = dev_get_by_index(&init_net, src_info->ipi6_ifindex);