Re: [PATCH] netlink: Ignore EHOSTUNREACH failures when duplicating routes

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Jun 18, 2024 at 01:56:11PM +0200, Stefano Brivio wrote:
> To implicitly resolve possible dependencies between routes as we
> duplicate them into the target namespace, we go through a set of n
> routes n times, and ignore EEXIST responses to netlink messages (we
> already inserted the route) and ENETUNREACH (we didn't insert the
> route yet, but we need to insert another one first).
> 
> Until now, we didn't ignore EHOSTUNREACH responses. However,
> NetworkManager users with multiple non-subnet routes for the same
> interface report that pasta exits with "no route to host" while
> duplicating routes.
> 
> This happens because NetworkManager sets the 'noprefixroute' attribute
> on addresses, meaning that the kernel won't create subnet routes
> automatically depending on the prefix length of the address. We copy
> this attribute as we copy the address into the target namespace, and
> as a result, the kernel doesn't create subnet routes in the target
> namespace either.
> 
> This means that the gateway for routes that are inserted later can be
> unreachable at some points during the sequence of route duplication.
> That is, we don't just have dependencies between regular routes, but
> we can also have dependencies between regular routes and subnet
> routes, as subnet routes are not automatically inserted in advance.

Nice explanation, thank you.

> Link: https://github.com/containers/podman/issues/22824
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  netlink.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/netlink.c b/netlink.c
> index 4dbddb2..0be4ea3 100644
> --- a/netlink.c
> +++ b/netlink.c
> @@ -655,7 +655,8 @@ int nl_route_dup(int s_src, unsigned int ifi_src,
>  			rc = nl_do(s_dst, nh, RTM_NEWROUTE,
>  				   (flags & ~NLM_F_DUMP_FILTERED) | NLM_F_CREATE,
>  				   nh->nlmsg_len);
> -			if (rc < 0 && rc != -ENETUNREACH && rc != -EEXIST)
> +			if (rc < 0 && rc != -EEXIST &&
> +			    rc != -ENETUNREACH && rc != -EHOSTUNREACH)
>  				return rc;
>  		}
>  	}

-- 
David Gibson (he or they)	| 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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