ip/ip6_gre: Fix non-point-to-point tunnel not generating IPv6 link local address

[ Upstream commit 30e2291f61f93f7132c060190f8360df52644ec1 ]

We recently found that our non-point-to-point tunnels were not
generating any IPv6 link local address and instead generating an
IPv6 compat address, breaking IPv6 communication on the tunnel.

Previously, addrconf_gre_config always would call addrconf_addr_gen
and generate a EUI64 link local address for the tunnel.
Then commit afa5a712fd86 changed the code path so that add_v4_addrs
is called but this only generates a compat IPv6 address for
non-point-to-point tunnels.

I assume the compat address is specifically for SIT tunnels so
have kept that only for SIT - GRE tunnels now always generate link
local addresses.

Fixes: afa5a712fd86 ("ip/ip6_gre: use the same logic as SIT interfaces when computing v6LL address")
Signed-off-by: Thomas Winter <Thomas.Winter@alliedtelesis.co.nz>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index eaecaf2ffe002af69c01b1f348ce7c6344cec7e0..e6c7edcf6834397ab7de0559d6ddb3c880aecd04 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3127,17 +3127,17 @@ static void add_v4_addrs(struct inet6_dev *idev)
                offset = sizeof(struct in6_addr) - 4;
        memcpy(&addr.s6_addr32[3], idev->dev->dev_addr + offset, 4);
 
-       if (idev->dev->flags&IFF_POINTOPOINT) {
+       if (!(idev->dev->flags & IFF_POINTOPOINT) && idev->dev->type == ARPHRD_SIT) {
+               scope = IPV6_ADDR_COMPATv4;
+               plen = 96;
+               pflags |= RTF_NONEXTHOP;
+       } else {
                if (idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_NONE)
                        return;
 
                addr.s6_addr32[0] = htonl(0xfe800000);
                scope = IFA_LINK;
                plen = 64;
-       } else {
-               scope = IPV6_ADDR_COMPATv4;
-               plen = 96;
-               pflags |= RTF_NONEXTHOP;
        }
 
        if (addr.s6_addr32[3]) {