[PATCH net] net: ipv6/addrconf: clamp temporary address's preferred lifetime to public address's

[Alex Henrie <alexhenrie24@gmail.com>]

Fixes: 629df6701c8a ("net: ipv6/addrconf: clamp preferred_lft to the minimum required")
Reported-by: Dan Moulding <dan@danm.net>
Closes: https://lore.kernel.org/netdev/20231221231115.12402-1-dan@danm.net/
Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
---
 net/ipv6/addrconf.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 2692a7b24c40..37141d3417fe 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -1337,7 +1337,7 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block)
 	unsigned long tmp_tstamp, age;
 	unsigned long regen_advance;
 	unsigned long now = jiffies;
-	s32 cnf_temp_preferred_lft;
+	s32 cnf_temp_preferred_lft, if_public_preferred_lft;
 	struct inet6_ifaddr *ift;
 	struct ifa6_config cfg;
 	long max_desync_factor;
@@ -1394,11 +1394,13 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block)
 		}
 	}
 
+	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;
@@ -1414,20 +1416,34 @@ static int ipv6_create_tempaddr(struct inet6_ifaddr *ifp, bool block)
 	 *     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.
+	 *     ...
+	 *
+	 *     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)
+	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;
-		goto out;
+		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;
-- 
2.43.0