ipv6: introduce secret_stable to ipv6_devconf

This patch implements the procfs logic for the stable_address knob:
The secret is formatted as an ipv6 address and will be stored per
interface and per namespace. We track initialized flag and return EIO
errors until the secret is set.

We don't inherit the secret to newly created namespaces.

Cc: Erik Kline <[e-mail]>
Cc: Fernando Gont <[e-mail]>
Cc: Lorenzo Colitti <[e-mail]>
Cc: YOSHIFUJI Hideaki/吉藤英明 <[e-mail]>
Signed-off-by: Hannes Frederic Sowa <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/ipv6.h

···
 	__s32           ndisc_notify;
 	__s32		suppress_frag_ndisc;
 	__s32		accept_ra_mtu;
+	struct ipv6_stable_secret {
+		bool initialized;
+		struct in6_addr secret;
+	} stable_secret;
 	void		*sysctl;
 };
 

include/uapi/linux/ipv6.h

···
 	DEVCONF_ACCEPT_RA_FROM_LOCAL,
 	DEVCONF_USE_OPTIMISTIC,
 	DEVCONF_ACCEPT_RA_MTU,
+	DEVCONF_STABLE_SECRET,
 	DEVCONF_MAX
 };
 

net/ipv6/addrconf.c

···
 #include <linux/socket.h>
 #include <linux/sockios.h>
 #include <linux/net.h>
+#include <linux/inet.h>
 #include <linux/in6.h>
 #include <linux/netdevice.h>
 #include <linux/if_addr.h>
···
 #endif
 
 #define	INFINITY_LIFE_TIME	0xFFFFFFFF
+
+#define IPV6_MAX_STRLEN \
+	sizeof("ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255")
 
 static inline u32 cstamp_delta(unsigned long cstamp)
 {
···
 	.accept_dad		= 1,
 	.suppress_frag_ndisc	= 1,
 	.accept_ra_mtu		= 1,
+	.stable_secret		= {
+		.initialized = false,
+	}
 };
 
 static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
···
 	.accept_dad		= 1,
 	.suppress_frag_ndisc	= 1,
 	.accept_ra_mtu		= 1,
+	.stable_secret		= {
+		.initialized = false,
+	},
 };
 
 /* Check if a valid qdisc is available */
···
 	array[DEVCONF_SUPPRESS_FRAG_NDISC] = cnf->suppress_frag_ndisc;
 	array[DEVCONF_ACCEPT_RA_FROM_LOCAL] = cnf->accept_ra_from_local;
 	array[DEVCONF_ACCEPT_RA_MTU] = cnf->accept_ra_mtu;
+	/* we omit DEVCONF_STABLE_SECRET for now */
 }
 
 static inline size_t inet6_ifla6_size(void)
···
 	return ret;
 }
 
+static int addrconf_sysctl_stable_secret(struct ctl_table *ctl, int write,
+					 void __user *buffer, size_t *lenp,
+					 loff_t *ppos)
+{
+	int err;
+	struct in6_addr addr;
+	char str[IPV6_MAX_STRLEN];
+	struct ctl_table lctl = *ctl;
+	struct ipv6_stable_secret *secret = ctl->data;
+
+	lctl.maxlen = IPV6_MAX_STRLEN;
+	lctl.data = str;
+
+	if (!rtnl_trylock())
+		return restart_syscall();
+
+	if (!write && !secret->initialized) {
+		err = -EIO;
+		goto out;
+	}
+
+	if (!write) {
+		err = snprintf(str, sizeof(str), "%pI6",
+			       &secret->secret);
+		if (err >= sizeof(str)) {
+			err = -EIO;
+			goto out;
+		}
+	}
+
+	err = proc_dostring(&lctl, write, buffer, lenp, ppos);
+	if (err || !write)
+		goto out;
+
+	if (in6_pton(str, -1, addr.in6_u.u6_addr8, -1, NULL) != 1) {
+		err = -EIO;
+		goto out;
+	}
+
+	secret->initialized = true;
+	secret->secret = addr;
+
+out:
+	rtnl_unlock();
+
+	return err;
+}
 
 static struct addrconf_sysctl_table
 {
···
 			.proc_handler	= proc_dointvec,
 		},
 		{
+			.procname	= "stable_secret",
+			.data		= &ipv6_devconf.stable_secret,
+			.maxlen		= IPV6_MAX_STRLEN,
+			.mode		= 0600,
+			.proc_handler	= addrconf_sysctl_stable_secret,
+		},
+		{
 			/* sentinel */
 		}
 	},
···
 	/* these will be inherited by all namespaces */
 	dflt->autoconf = ipv6_defaults.autoconf;
 	dflt->disable_ipv6 = ipv6_defaults.disable_ipv6;
+
+	dflt->stable_secret.initialized = false;
+	all->stable_secret.initialized = false;
 
 	net->ipv6.devconf_all = all;
 	net->ipv6.devconf_dflt = dflt;