ipv6: add IFLA_INET6_RA_MTU to expose mtu value

The kernel provides a "/proc/sys/net/ipv6/conf/<iface>/mtu"
file, which can temporarily record the mtu value of the last
received RA message when the RA mtu value is lower than the
interface mtu, but this proc has following limitations:

(1) when the interface mtu (/sys/class/net/<iface>/mtu) is
updeated, mtu6 (/proc/sys/net/ipv6/conf/<iface>/mtu) will
be updated to the value of interface mtu;
(2) mtu6 (/proc/sys/net/ipv6/conf/<iface>/mtu) only affect
ipv6 connection, and not affect ipv4.

Therefore, when the mtu option is carried in the RA message,
there will be a problem that the user sometimes cannot obtain
RA mtu value correctly by reading mtu6.

After this patch set, if a RA message carries the mtu option,
you can send a netlink msg which nlmsg_type is RTM_GETLINK,
and then by parsing the attribute of IFLA_INET6_RA_MTU to
get the mtu value carried in the RA message received on the
inet6 device. In addition, you can also get a link notification
when ra_mtu is updated so it doesn't have to poll.

In this way, if the MTU values that the device receives from
the network in the PCO IPv4 and the RA IPv6 procedures are
different, the user can obtain the correct ipv6 ra_mtu value
and compare the value of ra_mtu and ipv4 mtu, then the device
can use the lower MTU value for both IPv4 and IPv6.

Signed-off-by: Rocco Yue <rocco.yue@mediatek.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20210827150412.9267-1-rocco.yue@mediatek.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/if_inet6.h b/include/net/if_inet6.h
index 42235c178b06e80cce1c63d54b3d462efac0f90a..653e7d0f65cb7a5e7458daf860215d1873c532e7 100644 (file)
--- a/include/net/if_inet6.h
+++ b/include/net/if_inet6.h
@@ -210,6 +210,8 @@ struct inet6_dev {
 
        unsigned long           tstamp; /* ipv6InterfaceTable update timestamp */
        struct rcu_head         rcu;
+
+       unsigned int            ra_mtu;
 };
 
 static inline void ipv6_eth_mc_map(const struct in6_addr *addr, char *buf)

diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index 8aad65b690540e8b845df3caad9629ba384db150..eebd3894fe89a0dfda36d79e1a291743220db613 100644 (file)
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -417,6 +417,7 @@ enum {
        IFLA_INET6_ICMP6STATS,  /* statistics (icmpv6)          */
        IFLA_INET6_TOKEN,       /* device token                 */
        IFLA_INET6_ADDR_GEN_MODE, /* implicit address generator mode */
+       IFLA_INET6_RA_MTU,      /* mtu carried in the RA message */
        __IFLA_INET6_MAX
 };
 

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 8381288a0d6ec4f2a8f77b958ff2ab03da9dff2a..17756f3ed33b269983ca73fafd46693e0567322e 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -394,6 +394,7 @@ static struct inet6_dev *ipv6_add_dev(struct net_device *dev)
                ndev->cnf.addr_gen_mode = IN6_ADDR_GEN_MODE_STABLE_PRIVACY;
 
        ndev->cnf.mtu6 = dev->mtu;
+       ndev->ra_mtu = 0;
        ndev->nd_parms = neigh_parms_alloc(dev, &nd_tbl);
        if (!ndev->nd_parms) {
                kfree(ndev);
@@ -3849,6 +3850,7 @@ restart:
        }
 
        idev->tstamp = jiffies;
+       idev->ra_mtu = 0;
 
        /* Last: Shot the device (if unregistered) */
        if (unregister) {
@@ -5543,6 +5545,7 @@ static inline size_t inet6_ifla6_size(void)
             + nla_total_size(ICMP6_MIB_MAX * 8) /* IFLA_INET6_ICMP6STATS */
             + nla_total_size(sizeof(struct in6_addr)) /* IFLA_INET6_TOKEN */
             + nla_total_size(1) /* IFLA_INET6_ADDR_GEN_MODE */
+            + nla_total_size(4) /* IFLA_INET6_RA_MTU */
             + 0;
 }
 
@@ -5651,6 +5654,10 @@ static int inet6_fill_ifla6_attrs(struct sk_buff *skb, struct inet6_dev *idev,
        if (nla_put_u8(skb, IFLA_INET6_ADDR_GEN_MODE, idev->cnf.addr_gen_mode))
                goto nla_put_failure;
 
+       if (idev->ra_mtu &&
+           nla_put_u32(skb, IFLA_INET6_RA_MTU, idev->ra_mtu))
+               goto nla_put_failure;
+
        return 0;
 
 nla_put_failure:
@@ -5767,6 +5774,9 @@ update_lft:
 static const struct nla_policy inet6_af_policy[IFLA_INET6_MAX + 1] = {
        [IFLA_INET6_ADDR_GEN_MODE]      = { .type = NLA_U8 },
        [IFLA_INET6_TOKEN]              = { .len = sizeof(struct in6_addr) },
+       [IFLA_INET6_RA_MTU]             = { .type = NLA_REJECT,
+                                           .reject_message =
+                                               "IFLA_INET6_RA_MTU can not be set" },
 };
 
 static int check_addr_gen_mode(int mode)

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index c467c6419893cddf845448c0e34eec37455a55ff..4b098521a44cd7a7dc9ff791265d52ea632b0e75 100644 (file)
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1391,12 +1391,6 @@ skip_defrtr:
                }
        }
 
-       /*
-        *      Send a notify if RA changed managed/otherconf flags or timer settings
-        */
-       if (send_ifinfo_notify)
-               inet6_ifinfo_notify(RTM_NEWLINK, in6_dev);
-
 skip_linkparms:
 
        /*
@@ -1496,6 +1490,11 @@ skip_routeinfo:
                memcpy(&n, ((u8 *)(ndopts.nd_opts_mtu+1))+2, sizeof(mtu));
                mtu = ntohl(n);
 
+               if (in6_dev->ra_mtu != mtu) {
+                       in6_dev->ra_mtu = mtu;
+                       send_ifinfo_notify = true;
+               }
+
                if (mtu < IPV6_MIN_MTU || mtu > skb->dev->mtu) {
                        ND_PRINTK(2, warn, "RA: invalid mtu: %d\n", mtu);
                } else if (in6_dev->cnf.mtu6 != mtu) {
@@ -1519,6 +1518,12 @@ skip_routeinfo:
                ND_PRINTK(2, warn, "RA: invalid RA options\n");
        }
 out:
+       /* Send a notify if RA changed managed/otherconf flags or
+        * timer settings or ra_mtu value
+        */
+       if (send_ifinfo_notify)
+               inet6_ifinfo_notify(RTM_NEWLINK, in6_dev);
+
        fib6_info_release(rt);
        if (neigh)
                neigh_release(neigh);

diff --git a/tools/include/uapi/linux/if_link.h b/tools/include/uapi/linux/if_link.h
index eb15f319aa571e96ce28bf6d6f2c5c20a98567bf..b3610fdd1feec345dee8df36bce3c9c4895c98a0 100644 (file)
--- a/tools/include/uapi/linux/if_link.h
+++ b/tools/include/uapi/linux/if_link.h
@@ -230,6 +230,7 @@ enum {
        IFLA_INET6_ICMP6STATS,  /* statistics (icmpv6)          */
        IFLA_INET6_TOKEN,       /* device token                 */
        IFLA_INET6_ADDR_GEN_MODE, /* implicit address generator mode */
+       IFLA_INET6_RA_MTU,      /* mtu carried in the RA message */
        __IFLA_INET6_MAX
 };