[PATCH v3 1/4] wiphy: add _generate_address_from_ssid

[James Prestwood <prestwoj@gmail.com>]

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This API is being added to support per-network MAC address
generation. The MAC is generated based on the network SSID
and the adapters permanent address using HMAC-SHA256. The
SHA digest is then constrained to make it MAC address
compliant.

Generating the MAC address like this will ensure that the
MAC remains the same each time a given SSID is connected to.
---
 src/wiphy.c | 34 ++++++++++++++++++++++++++++++----
 src/wiphy.h |  2 ++
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/src/wiphy.c b/src/wiphy.c
index e0929c09..b8e80b00 100644
--- a/src/wiphy.c
+++ b/src/wiphy.c
@@ -435,12 +435,10 @@ const uint8_t *wiphy_get_rm_enabled_capabilities(struct wiphy *wiphy)
 	return wiphy->rm_enabled_capabilities;
 }
 
-void wiphy_generate_random_address(struct wiphy *wiphy, uint8_t addr[static 6])
+static void wiphy_address_constrain(struct wiphy *wiphy, uint8_t addr[static 6])
 {
 	switch (mac_randomize_bytes) {
 	case 6:
-		l_getrandom(addr, 6);
-
 		/* Set the locally administered bit */
 		addr[0] |= 0x2;
 
@@ -448,7 +446,6 @@ void wiphy_generate_random_address(struct wiphy *wiphy, uint8_t addr[static 6])
 		addr[0] &= 0xfe;
 		break;
 	case 3:
-		l_getrandom(addr + 3, 3);
 		memcpy(addr, wiphy->permanent_addr, 3);
 		break;
 	}
@@ -464,6 +461,35 @@ void wiphy_generate_random_address(struct wiphy *wiphy, uint8_t addr[static 6])
 		addr[5] = 0x01;
 }
 
+void wiphy_generate_random_address(struct wiphy *wiphy, uint8_t addr[static 6])
+{
+	switch (mac_randomize_bytes) {
+	case 6:
+		l_getrandom(addr, 6);
+		break;
+	case 3:
+		l_getrandom(addr + 3, 3);
+		break;
+	}
+
+	wiphy_address_constrain(wiphy, addr);
+}
+
+void wiphy_generate_address_from_ssid(struct wiphy *wiphy, const char *ssid,
+					uint8_t addr[static 6])
+{
+	struct l_checksum *sha = l_checksum_new(L_CHECKSUM_SHA256);
+
+	l_checksum_update(sha, ssid, strlen(ssid));
+	l_checksum_update(sha, wiphy->permanent_addr,
+				sizeof(wiphy->permanent_addr));
+	l_checksum_get_digest(sha, addr, mac_randomize_bytes);
+
+	l_checksum_free(sha);
+
+	wiphy_address_constrain(wiphy, addr);
+}
+
 bool wiphy_constrain_freq_set(const struct wiphy *wiphy,
 						struct scan_freq_set *set)
 {
diff --git a/src/wiphy.h b/src/wiphy.h
index dff0e1bd..4d2a4e8f 100644
--- a/src/wiphy.h
+++ b/src/wiphy.h
@@ -82,6 +82,8 @@ const uint8_t *wiphy_get_extended_capabilities(struct wiphy *wiphy,
 const uint8_t *wiphy_get_rm_enabled_capabilities(struct wiphy *wiphy);
 
 void wiphy_generate_random_address(struct wiphy *wiphy, uint8_t addr[static 6]);
+void wiphy_generate_address_from_ssid(struct wiphy *wiphy, const char *ssid,
+					uint8_t addr[static 6]);
 
 uint32_t wiphy_state_watch_add(struct wiphy *wiphy,
 				wiphy_state_watch_func_t func, void *user_data,
-- 
2.21.1