[PATCH net-next] ipv6: Simplify link-local address generation for IPv6 GRE.

[PATCH net-next] ipv6: Simplify link-local address generation for IPv6 GRE.

[Guillaume Nault]

Since commit 3e6a0243ff00 ("gre: Fix again IPv6 link-local address
generation."), addrconf_gre_config() has stopped handling IP6GRE
devices specially and just calls the regular addrconf_addr_gen()
function to create their link-local IPv6 addresses.

We can thus avoid using addrconf_gre_config() for IP6GRE devices and
use the normal IPv6 initialisation path instead (that is, jump directly
to addrconf_dev_config() in addrconf_init_auto_addrs()).

See commit 3e6a0243ff00 ("gre: Fix again IPv6 link-local address
generation.") for a deeper explanation on how and why GRE devices
started handling their IPv6 link-local address generation specially,
why it was a problem, and why this is not even necessary in most cases
(especially for GRE over IPv6).

Signed-off-by: Guillaume Nault <gnault@redhat.com>
---
 net/ipv6/addrconf.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index ba2ec7c870cc..9c297974d3a6 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3208,7 +3208,7 @@ static void add_addr(struct inet6_dev *idev, const struct in6_addr *addr,
 	}
 }
 
-#if IS_ENABLED(CONFIG_IPV6_SIT) || IS_ENABLED(CONFIG_NET_IPGRE) || IS_ENABLED(CONFIG_IPV6_GRE)
+#if IS_ENABLED(CONFIG_IPV6_SIT) || IS_ENABLED(CONFIG_NET_IPGRE)
 static void add_v4_addrs(struct inet6_dev *idev)
 {
 	struct in6_addr addr;
@@ -3463,6 +3463,7 @@ static void addrconf_dev_config(struct net_device *dev)
 	    (dev->type != ARPHRD_IEEE1394) &&
 	    (dev->type != ARPHRD_TUNNEL6) &&
 	    (dev->type != ARPHRD_6LOWPAN) &&
+	    (dev->type != ARPHRD_IP6GRE) &&
 	    (dev->type != ARPHRD_TUNNEL) &&
 	    (dev->type != ARPHRD_NONE) &&
 	    (dev->type != ARPHRD_RAWIP)) {
@@ -3518,7 +3519,7 @@ static void addrconf_sit_config(struct net_device *dev)
 }
 #endif
 
-#if IS_ENABLED(CONFIG_NET_IPGRE) || IS_ENABLED(CONFIG_IPV6_GRE)
+#if IS_ENABLED(CONFIG_NET_IPGRE)
 static void addrconf_gre_config(struct net_device *dev)
 {
 	struct inet6_dev *idev;
@@ -3536,7 +3537,7 @@ static void addrconf_gre_config(struct net_device *dev)
 	 * 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 &&
+	if (!(*(__be32 *)dev->dev_addr == 0 &&
 	      idev->cnf.addr_gen_mode == IN6_ADDR_GEN_MODE_EUI64)) {
 		addrconf_addr_gen(idev, true);
 		return;
@@ -3557,8 +3558,7 @@ static void addrconf_init_auto_addrs(struct net_device *dev)
 		addrconf_sit_config(dev);
 		break;
 #endif
-#if IS_ENABLED(CONFIG_NET_IPGRE) || IS_ENABLED(CONFIG_IPV6_GRE)
-	case ARPHRD_IP6GRE:
+#if IS_ENABLED(CONFIG_NET_IPGRE)
 	case ARPHRD_IPGRE:
 		addrconf_gre_config(dev);
 		break;
-- 
2.39.2

Re: [PATCH net-next] ipv6: Simplify link-local address generation for IPv6 GRE.

[Ido Schimmel]

On Mon, Jun 16, 2025 at 01:58:29PM +0200, Guillaume Nault wrote:
> Since commit 3e6a0243ff00 ("gre: Fix again IPv6 link-local address
> generation."), addrconf_gre_config() has stopped handling IP6GRE
> devices specially and just calls the regular addrconf_addr_gen()
> function to create their link-local IPv6 addresses.
> 
> We can thus avoid using addrconf_gre_config() for IP6GRE devices and
> use the normal IPv6 initialisation path instead (that is, jump directly
> to addrconf_dev_config() in addrconf_init_auto_addrs()).
> 
> See commit 3e6a0243ff00 ("gre: Fix again IPv6 link-local address
> generation.") for a deeper explanation on how and why GRE devices
> started handling their IPv6 link-local address generation specially,
> why it was a problem, and why this is not even necessary in most cases
> (especially for GRE over IPv6).
> 
> Signed-off-by: Guillaume Nault <gnault@redhat.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

Re: [PATCH net-next] ipv6: Simplify link-local address generation for IPv6 GRE.

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Mon, 16 Jun 2025 13:58:29 +0200 you wrote:
> Since commit 3e6a0243ff00 ("gre: Fix again IPv6 link-local address
> generation."), addrconf_gre_config() has stopped handling IP6GRE
> devices specially and just calls the regular addrconf_addr_gen()
> function to create their link-local IPv6 addresses.
> 
> We can thus avoid using addrconf_gre_config() for IP6GRE devices and
> use the normal IPv6 initialisation path instead (that is, jump directly
> to addrconf_dev_config() in addrconf_init_auto_addrs()).
> 
> [...]

Here is the summary with links:
  - [net-next] ipv6: Simplify link-local address generation for IPv6 GRE.
    https://git.kernel.org/netdev/net-next/c/d3623dd5bd4e

You are awesome, thank you!
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