5.15-stable review patch. If anyone has any objections, please let me know.
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From: Guillaume Nault gnault@redhat.com
[ Upstream commit 183185a18ff96751db52a46ccf93fff3a1f42815 ]
Use addrconf_addr_gen() to generate IPv6 link-local addresses on GRE devices in most cases and fall back to using add_v4_addrs() only in case the GRE configuration is incompatible with addrconf_addr_gen().
GRE used to use addrconf_addr_gen() until commit e5dd729460ca ("ip/ip6_gre: use the same logic as SIT interfaces when computing v6LL address") restricted this use to gretap and ip6gretap devices, and created add_v4_addrs() (borrowed from SIT) for non-Ethernet GRE ones.
The original problem came when commit 9af28511be10 ("addrconf: refuse isatap eui64 for INADDR_ANY") made __ipv6_isatap_ifid() fail when its addr parameter was 0. The commit says that this would create an invalid address, however, I couldn't find any RFC saying that the generated interface identifier would be wrong. Anyway, since gre over IPv4 devices pass their local tunnel address to __ipv6_isatap_ifid(), that commit broke their IPv6 link-local address generation when the local address was unspecified.
Then commit e5dd729460ca ("ip/ip6_gre: use the same logic as SIT interfaces when computing v6LL address") tried to fix that case by defining add_v4_addrs() and calling it to generate the IPv6 link-local address instead of using addrconf_addr_gen() (apart for gretap and ip6gretap devices, which would still use the regular addrconf_addr_gen(), since they have a MAC address).
That broke several use cases because add_v4_addrs() isn't properly integrated into the rest of IPv6 Neighbor Discovery code. Several of these shortcomings have been fixed over time, but add_v4_addrs() remains broken on several aspects. In particular, it doesn't send any Router Sollicitations, so the SLAAC process doesn't start until the interface receives a Router Advertisement. Also, add_v4_addrs() mostly ignores the address generation mode of the interface (/proc/sys/net/ipv6/conf/*/addr_gen_mode), thus breaking the IN6_ADDR_GEN_MODE_RANDOM and IN6_ADDR_GEN_MODE_STABLE_PRIVACY cases.
Fix the situation by using add_v4_addrs() only in the specific scenario where the normal method would fail. That is, for interfaces that have all of the following characteristics:
* run over IPv4, * transport IP packets directly, not Ethernet (that is, not gretap interfaces), * tunnel endpoint is INADDR_ANY (that is, 0), * device address generation mode is EUI64.
In all other cases, revert back to the regular addrconf_addr_gen().
Also, remove the special case for ip6gre interfaces in add_v4_addrs(), since ip6gre devices now always use addrconf_addr_gen() instead.
Fixes: e5dd729460ca ("ip/ip6_gre: use the same logic as SIT interfaces when computing v6LL address") Signed-off-by: Guillaume Nault gnault@redhat.com Reviewed-by: Ido Schimmel idosch@nvidia.com Link: https://patch.msgid.link/559c32ce5c9976b269e6337ac9abb6a96abe5096.1741375285... Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv6/addrconf.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c index 932a10f64adcb..f5cca40b71610 100644 --- a/net/ipv6/addrconf.c +++ b/net/ipv6/addrconf.c @@ -3145,16 +3145,13 @@ static void add_v4_addrs(struct inet6_dev *idev) struct in6_addr addr; struct net_device *dev; struct net *net = dev_net(idev->dev); - int scope, plen, offset = 0; + int scope, plen; u32 pflags = 0;
ASSERT_RTNL();
memset(&addr, 0, sizeof(struct in6_addr)); - /* in case of IP6GRE the dev_addr is an IPv6 and therefore we use only the last 4 bytes */ - if (idev->dev->addr_len == sizeof(struct in6_addr)) - offset = sizeof(struct in6_addr) - 4; - memcpy(&addr.s6_addr32[3], idev->dev->dev_addr + offset, 4); + memcpy(&addr.s6_addr32[3], idev->dev->dev_addr, 4);
if (!(idev->dev->flags & IFF_POINTOPOINT) && idev->dev->type == ARPHRD_SIT) { scope = IPV6_ADDR_COMPATv4; @@ -3462,7 +3459,13 @@ static void addrconf_gre_config(struct net_device *dev) return; }
- if (dev->type == ARPHRD_ETHER) { + /* Generate the IPv6 link-local address using addrconf_addr_gen(), + * unless we have an IPv4 GRE device not bound to an IP address and + * which is in EUI64 mode (as __ipv6_isatap_ifid() would fail in this + * case). Such devices fall back to add_v4_addrs() instead. + */ + if (!(dev->type == ARPHRD_IPGRE && *(__be32 *)dev->dev_addr == 0 && + idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_EUI64)) { addrconf_addr_gen(idev, true); return; }