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 e5dd729460 ("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 9af28511be ("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 e5dd729460 ("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.
Note:
This patch was originally applied as commit 183185a18f ("gre: Fix
IPv6 link-local address generation."). However, it was then reverted
by commit fc486c2d06 ("Revert "gre: Fix IPv6 link-local address
generation."") because it uncovered another bug that ended up
breaking net/forwarding/ip6gre_custom_multipath_hash.sh. That other
bug has now been fixed by commit 4d0ab3a688 ("ipv6: Start path
selection from the first nexthop"). Therefore we can now revive this
GRE patch (no changes since original commit 183185a18f ("gre: Fix
IPv6 link-local address generation.").
Fixes: e5dd729460 ("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/a88cc5c4811af36007645d610c95102dccb360a6.1746225214.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
3e6a0243ff