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

26 Apr 2024

...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 
---
 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,
-- 
2.43.0

    

Stefano Brivio

David Gibson

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