Merge branch 'net-ipv6-addrconf-ensure-that-temporary-addresses-preferred-lifetimes-are-in-the-valid-range'

Alex Henrie says:

====================
net: ipv6/addrconf: ensure that temporary addresses' preferred lifetimes are in the valid range

No changes from v2, but there are only four patches now because the
first patch has already been applied.

https://lore.kernel.org/all/20230829054623.104293-1-alexhenrie24@gmail.com/
====================

Link: https://lore.kernel.org/r/20231024212312.299370-1-alexhenrie24@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2 files changed, 22 insertions, 7 deletions

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index e7ec9026e5db..4dfe0d9a57bb 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -2502,12 +2502,18 @@ use_tempaddr - INTEGER
 		* -1 (for point-to-point devices and loopback devices)
 
 temp_valid_lft - INTEGER
-	valid lifetime (in seconds) for temporary addresses.
+	valid lifetime (in seconds) for temporary addresses. If less than the
+	minimum required lifetime (typically 5 seconds), temporary addresses
+	will not be created.
 
 	Default: 172800 (2 days)
 
 temp_prefered_lft - INTEGER
-	Preferred lifetime (in seconds) for temporary addresses.
+	Preferred lifetime (in seconds) for temporary addresses. If
+	temp_prefered_lft is less than the minimum required lifetime (typically
+	5 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.
 
 	Default: 86400 (1 day)
 
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index c2d471ad7922..3aaea56b5166 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1399,6 +1399,7 @@ retry:
 			      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, cfg.valid_lft, cfg.preferred_lft);
 
 	cfg.plen = ifp->prefix_len;
 	tmp_tstamp = ifp->tstamp;
@@ -1406,15 +1407,23 @@ 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.
+	 *
+	 * Clamp the preferred lifetime to a minimum of regen_advance, unless
+	 * that would exceed valid_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) {
+	if (cfg.preferred_lft <= regen_advance + age)
+		cfg.preferred_lft = regen_advance + age + 1;
+	if (cfg.preferred_lft > cfg.valid_lft) {
 		in6_ifa_put(ifp);
 		in6_dev_put(idev);
 		ret = -1;