netdev - [PATCH net] ipv6: clear RA flags when adding a static route

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Message-ID: <20251110230436.5625-1-fmancera@suse.de>
Date: Tue, 11 Nov 2025 00:04:36 +0100
From: Fernando Fernandez Mancera <fmancera@...e.de>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	dsahern@...nel.org,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	Fernando Fernandez Mancera <fmancera@...e.de>,
	Garri Djavadyan <g.djavadyan@...il.com>
Subject: [PATCH net] ipv6: clear RA flags when adding a static route

When an IPv6 Router Advertisement (RA) is received for a prefix, the
kernel creates the corresponding on-link route with flags RTF_ADDRCONF
and RTF_PREFIX_RT configured and RTF_EXPIRES if lifetime is set.

If later a user configures a static IPv6 address on the same prefix the
kernel clears the RTF_EXPIRES flag but it doesn't clear the RTF_ADDRCONF
and RTF_PREFIX_RT. When the next RA for that prefix is received, the
kernel sees the route as RA-learned and wrongly configures back the
lifetime. This is problematic because if the route expires, the static
address won't have the corresponding on-link route.

This fix clears the RTF_ADDRCONF and RTF_PREFIX_RT flags preventing that
the lifetime is configured when the next RA arrives. If the static
address is deleted, the route becomes RA-learned again.

Fixes: 14ef37b6d00e ("ipv6: fix route lookup in addrconf_prefix_rcv()")
Reported-by: Garri Djavadyan <g.djavadyan@...il.com>
Closes: https://lore.kernel.org/netdev/ba807d39aca5b4dcf395cc11dca61a130a52cfd3.camel@gmail.com/
Signed-off-by: Fernando Fernandez Mancera <fmancera@...e.de>
---
Note: this has been broken probably since forever but I belive the
commit in the fixes tag was aiming to fix this too. Anyway, any
recommendation for a fixes tag is welcomed.
---
 net/ipv6/ip6_fib.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 02c16909f618..2111af022d94 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -1138,6 +1138,10 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,
 					fib6_set_expires(iter, rt->expires);
 					fib6_add_gc_list(iter);
 				}
+				if (!(rt->fib6_flags & (RTF_ADDRCONF | RTF_PREFIX_RT))) {
+					iter->fib6_flags &= ~RTF_ADDRCONF;
+					iter->fib6_flags &= ~RTF_PREFIX_RT;
+				}

 				if (rt->fib6_pmtu)
 					fib6_metric_set(iter, RTAX_MTU,
-- 
2.51.0