[PATCH] netlink: Use IFA_F_NODAD also while duplicating addresses from the host

[PATCH] netlink: Use IFA_F_NODAD also while duplicating addresses from the host

[Stefano Brivio]

...not just for a single set address (legacy operation with
--no-copy-addrs). I forgot to add this to nl_addr_dup().

Note that we can have two version of flags: the 8-bit ifa_flags in
ifaddrmsg, and the newer 32-bit version as IFA_FLAGS attribute, which
is given priority if present. Make sure IFA_F_NODAD is set in both.

Without this, a Podman user reports, something on the lines of:
  pasta --config-net -- ping -c1 -6 passt.top

would fail as the kernel would start Duplicate Address Detection
once we configure the address, which can't really work (and doesn't
make sense) in this case.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 netlink.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/netlink.c b/netlink.c
index 447fea2..b3897e6 100644
--- a/netlink.c
+++ b/netlink.c
@@ -804,6 +804,8 @@ int nl_addr_dup(int s_src, unsigned int ifi_src,
 			continue;
 
 		ifa->ifa_index = ifi_dst;
+		/* Same as nl_addr_set(), but here it's more than a default */
+		ifa->ifa_flags |= IFA_F_NODAD;
 
 		for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na);
 		     rta = RTA_NEXT(rta, na)) {
@@ -811,6 +813,10 @@ int nl_addr_dup(int s_src, unsigned int ifi_src,
 			if (rta->rta_type == IFA_LABEL ||
 			    rta->rta_type == IFA_CACHEINFO)
 				rta->rta_type = IFA_UNSPEC;
+
+			/* If 32-bit flags are used, add IFA_F_NODAD there */
+			if (rta->rta_type == IFA_FLAGS)
+				*(uint32_t *)RTA_DATA(rta) |= IFA_F_NODAD;
 		}
 
 		rc = nl_do(s_dst, nh, RTM_NEWADDR,
-- 
@@ -804,6 +804,8 @@ int nl_addr_dup(int s_src, unsigned int ifi_src,
 			continue;
 
 		ifa->ifa_index = ifi_dst;
+		/* Same as nl_addr_set(), but here it's more than a default */
+		ifa->ifa_flags |= IFA_F_NODAD;
 
 		for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na);
 		     rta = RTA_NEXT(rta, na)) {
@@ -811,6 +813,10 @@ int nl_addr_dup(int s_src, unsigned int ifi_src,
 			if (rta->rta_type == IFA_LABEL ||
 			    rta->rta_type == IFA_CACHEINFO)
 				rta->rta_type = IFA_UNSPEC;
+
+			/* If 32-bit flags are used, add IFA_F_NODAD there */
+			if (rta->rta_type == IFA_FLAGS)
+				*(uint32_t *)RTA_DATA(rta) |= IFA_F_NODAD;
 		}
 
 		rc = nl_do(s_dst, nh, RTM_NEWADDR,
-- 
2.43.0

Re: [PATCH] netlink: Use IFA_F_NODAD also while duplicating addresses from the host

[David Gibson]

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On Fri, Apr 26, 2024 at 12:10:15AM +0200, Stefano Brivio wrote:
> ...not just for a single set address (legacy operation with
> --no-copy-addrs). I forgot to add this to nl_addr_dup().
> 
> Note that we can have two version of flags: the 8-bit ifa_flags in
> ifaddrmsg, and the newer 32-bit version as IFA_FLAGS attribute, which
> is given priority if present. Make sure IFA_F_NODAD is set in both.
> 
> Without this, a Podman user reports, something on the lines of:
>   pasta --config-net -- ping -c1 -6 passt.top
> 
> would fail as the kernel would start Duplicate Address Detection
> once we configure the address, which can't really work (and doesn't
> make sense) in this case.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

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

> ---
>  netlink.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/netlink.c b/netlink.c
> index 447fea2..b3897e6 100644
> --- a/netlink.c
> +++ b/netlink.c
> @@ -804,6 +804,8 @@ int nl_addr_dup(int s_src, unsigned int ifi_src,
>  			continue;
>  
>  		ifa->ifa_index = ifi_dst;
> +		/* Same as nl_addr_set(), but here it's more than a default */
> +		ifa->ifa_flags |= IFA_F_NODAD;
>  
>  		for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na);
>  		     rta = RTA_NEXT(rta, na)) {
> @@ -811,6 +813,10 @@ int nl_addr_dup(int s_src, unsigned int ifi_src,
>  			if (rta->rta_type == IFA_LABEL ||
>  			    rta->rta_type == IFA_CACHEINFO)
>  				rta->rta_type = IFA_UNSPEC;
> +
> +			/* If 32-bit flags are used, add IFA_F_NODAD there */
> +			if (rta->rta_type == IFA_FLAGS)
> +				*(uint32_t *)RTA_DATA(rta) |= IFA_F_NODAD;
>  		}
>  
>  		rc = nl_do(s_dst, nh, RTM_NEWADDR,

-- 
David Gibson			| 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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