Merge branch 'net-ipv6-addrconf-ensure-that-temporary-addresses-preferred-lifetimes-are-long-enough'

Alex Henrie says:

====================
net: ipv6/addrconf: ensure that temporary addresses' preferred lifetimes are long enough

v2 corrects and updates the documentation for these features.

Changes from v1:
- Update the typical minimum lifetime stated in the documentation, and
  make it a range to emphasize the variability
- Fix spelling of "determine" in the documentation
- Mention RFC 8981's requirements in the documentation
- Arrange variables in "reverse Christmas tree"
- Update documentation of what happens if temp_prefered_lft is less
  than the minimum required lifetime

Thanks to David, Paolo, and Dan for your feedback.
====================

Link: https://lore.kernel.org/r/20240214062711.608363-1-alexhenrie24@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

4 files changed, 68 insertions, 19 deletions

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 7afff42612e9..bd50df6a5a42 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -2503,7 +2503,7 @@ use_tempaddr - INTEGER
 
 temp_valid_lft - INTEGER
 	valid lifetime (in seconds) for temporary addresses. If less than the
-	minimum required lifetime (typically 5 seconds), temporary addresses
+	minimum required lifetime (typically 5-7 seconds), temporary addresses
 	will not be created.
 
 	Default: 172800 (2 days)
@@ -2511,7 +2511,7 @@ temp_valid_lft - INTEGER
 temp_prefered_lft - INTEGER
 	Preferred lifetime (in seconds) for temporary addresses. If
 	temp_prefered_lft is less than the minimum required lifetime (typically
-	5 seconds), temporary addresses will not be created. If
+	5-7 seconds), the preferred lifetime is the minimum required. If
 	temp_prefered_lft is greater than temp_valid_lft, the preferred lifetime
 	is temp_valid_lft.
 
@@ -2535,6 +2535,16 @@ max_desync_factor - INTEGER
 
 	Default: 600
 
+regen_min_advance - INTEGER
+	How far in advance (in seconds), at minimum, to create a new temporary
+	address before the current one is deprecated. This value is added to
+	the amount of time that may be required for duplicate address detection
+	to determine when to create a new address. Linux permits setting this
+	value to less than the default of 2 seconds, but a value less than 2
+	does not conform to RFC 8981.
+
+	Default: 2
+
 regen_max_retry - INTEGER
 	Number of attempts before give up attempting to generate
 	valid temporary addresses.
diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 5e605e384aac..ef3aa060a289 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -27,6 +27,7 @@ struct ipv6_devconf {
 	__s32		use_tempaddr;
 	__s32		temp_valid_lft;
 	__s32		temp_prefered_lft;
+	__s32		regen_min_advance;
 	__s32		regen_max_retry;
 	__s32		max_desync_factor;
 	__s32		max_addresses;
diff --git a/include/net/addrconf.h b/include/net/addrconf.h
index 61ebe723ee4d..30d6f1e84e46 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -8,8 +8,9 @@
 
 #define MIN_VALID_LIFETIME		(2*3600)	/* 2 hours */
 
-#define TEMP_VALID_LIFETIME		(7*86400)
-#define TEMP_PREFERRED_LIFETIME		(86400)
+#define TEMP_VALID_LIFETIME		(7*86400)       /* 1 week */
+#define TEMP_PREFERRED_LIFETIME		(86400)         /* 24 hours */
+#define REGEN_MIN_ADVANCE		(2)             /* 2 seconds */
 #define REGEN_MAX_RETRY			(3)
 #define MAX_DESYNC_FACTOR		(600)
 
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 2c1ed642e3f4..d3f4b7b9cf1f 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -195,6 +195,7 @@ static struct ipv6_devconf ipv6_devconf __read_mostly = {
 	.use_tempaddr		= 0,
 	.temp_valid_lft		= TEMP_VALID_LIFETIME,
 	.temp_prefered_lft	= TEMP_PREFERRED_LIFETIME,
+	.regen_min_advance	= REGEN_MIN_ADVANCE,
 	.regen_max_retry	= REGEN_MAX_RETRY,
 	.max_desync_factor	= MAX_DESYNC_FACTOR,
 	.max_addresses		= IPV6_MAX_ADDRESSES,
@@ -257,6 +258,7 @@ static struct ipv6_devconf ipv6_devconf_dflt __read_mostly = {
 	.use_tempaddr		= 0,
 	.temp_valid_lft		= TEMP_VALID_LIFETIME,
 	.temp_prefered_lft	= TEMP_PREFERRED_LIFETIME,
+	.regen_min_advance	= REGEN_MIN_ADVANCE,
 	.regen_max_retry	= REGEN_MAX_RETRY,
 	.max_desync_factor	= MAX_DESYNC_FACTOR,
 	.max_addresses		= IPV6_MAX_ADDRESSES,
@@ -1339,12 +1341,20 @@ out:
 	in6_ifa_put(ifp);
 }
 
+static unsigned long ipv6_get_regen_advance(struct inet6_dev *idev)
+{
+	return idev->cnf.regen_min_advance + idev->cnf.regen_max_retry *
+			idev->cnf.dad_transmits *
+			max(NEIGH_VAR(idev->nd_parms, RETRANS_TIME), HZ/100) / HZ;
+}
+
 static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block)
 {
 	struct inet6_dev *idev = ifp->idev;
 	unsigned long tmp_tstamp, age;
 	unsigned long regen_advance;
 	unsigned long now = jiffies;
+	u32 if_public_preferred_lft;
 	s32 cnf_temp_preferred_lft;
 	struct inet6_ifaddr *ift;
 	struct ifa6_config cfg;
@@ -1380,9 +1390,7 @@ retry:
 
 	age = (now - ifp->tstamp) / HZ;
 
-	regen_advance = idev->cnf.regen_max_retry *
-			idev->cnf.dad_transmits *
-			max(NEIGH_VAR(idev->nd_parms, RETRANS_TIME), HZ/100) / HZ;
+	regen_advance = ipv6_get_regen_advance(idev);
 
 	/* recalculate max_desync_factor each time and update
 	 * idev->desync_factor if it's larger
@@ -1402,11 +1410,13 @@ retry:
 		}
 	}
 
+	if_public_preferred_lft = ifp->prefered_lft;
+
 	memset(&cfg, 0, sizeof(cfg));
 	cfg.valid_lft = min_t(__u32, ifp->valid_lft,
 			      idev->cnf.temp_valid_lft + age);
 	cfg.preferred_lft = cnf_temp_preferred_lft + age - idev->desync_factor;
-	cfg.preferred_lft = min_t(__u32, ifp->prefered_lft, cfg.preferred_lft);
+	cfg.preferred_lft = min_t(__u32, if_public_preferred_lft, cfg.preferred_lft);
 	cfg.preferred_lft = min_t(__u32, cfg.valid_lft, cfg.preferred_lft);
 
 	cfg.plen = ifp->prefix_len;
@@ -1415,19 +1425,41 @@ retry:
 
 	write_unlock_bh(&idev->lock);
 
-	/* A temporary address is created only if this calculated Preferred
-	 * Lifetime is greater than REGEN_ADVANCE time units.  In particular,
-	 * an implementation must not create a temporary address with a zero
-	 * Preferred Lifetime.
+	/* From RFC 4941:
+	 *
+	 *     A temporary address is created only if this calculated Preferred
+	 *     Lifetime is greater than REGEN_ADVANCE time units.  In
+	 *     particular, an implementation must not create a temporary address
+	 *     with a zero Preferred Lifetime.
+	 *
+	 *     ...
+	 *
+	 *     When creating a temporary address, the lifetime values MUST be
+	 *     derived from the corresponding prefix as follows:
+	 *
+	 *     ...
+	 *
+	 *     *  Its Preferred Lifetime is the lower of the Preferred Lifetime
+	 *        of the public address or TEMP_PREFERRED_LIFETIME -
+	 *        DESYNC_FACTOR.
+	 *
+	 * To comply with the RFC's requirements, clamp the preferred lifetime
+	 * to a minimum of regen_advance, unless that would exceed valid_lft or
+	 * ifp->prefered_lft.
+	 *
 	 * Use age calculation as in addrconf_verify to avoid unnecessary
 	 * temporary addresses being generated.
 	 */
 	age = (now - tmp_tstamp + ADDRCONF_TIMER_FUZZ_MINUS) / HZ;
 	if (cfg.preferred_lft <= regen_advance + age) {
-		in6_ifa_put(ifp);
-		in6_dev_put(idev);
-		ret = -1;
-		goto out;
+		cfg.preferred_lft = regen_advance + age + 1;
+		if (cfg.preferred_lft > cfg.valid_lft ||
+		    cfg.preferred_lft > if_public_preferred_lft) {
+			in6_ifa_put(ifp);
+			in6_dev_put(idev);
+			ret = -1;
+			goto out;
+		}
 	}
 
 	cfg.ifa_flags = IFA_F_TEMPORARY;
@@ -4595,9 +4627,7 @@ restart:
 			    !ifp->regen_count && ifp->ifpub) {
 				/* This is a non-regenerated temporary addr. */
 
-				unsigned long regen_advance = ifp->idev->cnf.regen_max_retry *
-					ifp->idev->cnf.dad_transmits *
-					max(NEIGH_VAR(ifp->idev->nd_parms, RETRANS_TIME), HZ/100) / HZ;
+				unsigned long regen_advance = ipv6_get_regen_advance(ifp->idev);
 
 				if (age + regen_advance >= ifp->prefered_lft) {
 					struct inet6_ifaddr *ifpub = ifp->ifpub;
@@ -6817,6 +6847,13 @@ static const struct ctl_table addrconf_sysctl[] = {
 		.proc_handler	= proc_dointvec,
 	},
 	{
+		.procname       = "regen_min_advance",
+		.data           = &ipv6_devconf.regen_min_advance,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = proc_dointvec,
+	},
+	{
 		.procname	= "regen_max_retry",
 		.data		= &ipv6_devconf.regen_max_retry,
 		.maxlen		= sizeof(int),