[PATCH] netlink: Drop nexthop state flags from routes we duplicate

[PATCH] netlink: Drop nexthop state flags from routes we duplicate

[Stefano Brivio]

The kernel doesn't like those (EINVAL) on RTM_NEWROUTE, as they are
flags representing states, not configuration.

Link: https://github.com/containers/podman/discussions/27104
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 netlink.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/netlink.c b/netlink.c
index 8f82e73..c436780 100644
--- a/netlink.c
+++ b/netlink.c
@@ -565,6 +565,11 @@ int nl_route_dup(int s_src, unsigned int ifi_src,
 		if (nh->nlmsg_type != RTM_NEWROUTE)
 			continue;
 
+		/* nexthop state flags don't apply to freshly created routes,
+		 * and the kernel will refuse our route if they are set.
+		 */
+		rtm->rtm_flags &= ~RTNH_COMPARE_MASK;
+
 		for (rta = RTM_RTA(rtm), na = RTM_PAYLOAD(nh); RTA_OK(rta, na);
 		     rta = RTA_NEXT(rta, na)) {
 			/* RTA_OIF and RTA_MULTIPATH attributes carry the
-- 
2.43.0

Re: [PATCH] netlink: Drop nexthop state flags from routes we duplicate

[David Gibson]

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On Thu, Sep 18, 2025 at 06:33:50PM +0200, Stefano Brivio wrote:
> The kernel doesn't like those (EINVAL) on RTM_NEWROUTE, as they are
> flags representing states, not configuration.
> 
> Link: https://github.com/containers/podman/discussions/27104
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Aha!, nice catch.

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

> ---
>  netlink.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/netlink.c b/netlink.c
> index 8f82e73..c436780 100644
> --- a/netlink.c
> +++ b/netlink.c
> @@ -565,6 +565,11 @@ int nl_route_dup(int s_src, unsigned int ifi_src,
>  		if (nh->nlmsg_type != RTM_NEWROUTE)
>  			continue;
>  
> +		/* nexthop state flags don't apply to freshly created routes,
> +		 * and the kernel will refuse our route if they are set.
> +		 */
> +		rtm->rtm_flags &= ~RTNH_COMPARE_MASK;
> +
>  		for (rta = RTM_RTA(rtm), na = RTM_PAYLOAD(nh); RTA_OK(rta, na);
>  		     rta = RTA_NEXT(rta, na)) {
>  			/* RTA_OIF and RTA_MULTIPATH attributes carry the
> -- 
> 2.43.0
> 

-- 
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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Re: [PATCH] netlink: Drop nexthop state flags from routes we duplicate

[Paul Holzinger]

On 18/09/2025 18:33, Stefano Brivio wrote:
> The kernel doesn't like those (EINVAL) on RTM_NEWROUTE, as they are
> flags representing states, not configuration.
>
> Link: https://github.com/containers/podman/discussions/27104
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: Paul Holzinger <pholzing@redhat.com>
> ---
>   netlink.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/netlink.c b/netlink.c
> index 8f82e73..c436780 100644
> --- a/netlink.c
> +++ b/netlink.c
> @@ -565,6 +565,11 @@ int nl_route_dup(int s_src, unsigned int ifi_src,
>   		if (nh->nlmsg_type != RTM_NEWROUTE)
>   			continue;
>   
> +		/* nexthop state flags don't apply to freshly created routes,
> +		 * and the kernel will refuse our route if they are set.
> +		 */
> +		rtm->rtm_flags &= ~RTNH_COMPARE_MASK;
> +
>   		for (rta = RTM_RTA(rtm), na = RTM_PAYLOAD(nh); RTA_OK(rta, na);
>   		     rta = RTA_NEXT(rta, na)) {
>   			/* RTA_OIF and RTA_MULTIPATH attributes carry the

-- 
Paul Holzinger