hostapd: fix OWE association with mbedtls

The code for hostapd-mbedtls did not work when used for OWE association.

When handling association requests, the buffer offsets and length
assumptions were incorrect, leading to never calculating the y point,
thus denying association.

Also when crafting the association response, the buffer contained the
trailing key-type.

Fix up both issues to adhere to the specification and make
hostapd-mbedtls work with the OWE security type.

Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit 39341f422f895a37b405b753c3630b1bdc9b8c6e)

2 files changed, 92 insertions, 1 deletions

diff --git a/package/network/services/hostapd/Makefile b/package/network/services/hostapd/Makefile
index 64048a963a..73ec5e198d 100644
--- a/package/network/services/hostapd/Makefile
+++ b/package/network/services/hostapd/Makefile
@@ -5,7 +5,7 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=hostapd
-PKG_RELEASE:=4
+PKG_RELEASE:=5
 
 PKG_SOURCE_URL:=http://w1.fi/hostap.git
 PKG_SOURCE_PROTO:=git
diff --git a/package/network/services/hostapd/patches/135-mbedtls-fix-owe-association.patch b/package/network/services/hostapd/patches/135-mbedtls-fix-owe-association.patch
new file mode 100644
index 0000000000..0c29432d3f
--- /dev/null
+++ b/package/network/services/hostapd/patches/135-mbedtls-fix-owe-association.patch
@@ -0,0 +1,91 @@
+The code for hostapd-mbedtls did not work when used for OWE association.
+
+When handling association requests, the buffer offsets and length assumptions were incorrect, leading to never calculating the y point, thus denying association.
+
+Also when crafting the association response, the buffer contained the trailing key-type.
+
+Fix up both issues to adhere to the specification and make hostapd-mbedtls work with the OWE security type.
+
+--- a/src/crypto/crypto_mbedtls.c
++++ b/src/crypto/crypto_mbedtls.c
+@@ -2299,25 +2299,30 @@ struct crypto_ecdh * crypto_ecdh_init2(i
+ struct wpabuf * crypto_ecdh_get_pubkey(struct crypto_ecdh *ecdh, int inc_y)
+ {
+ 	mbedtls_ecp_group *grp = &ecdh->grp;
+-	size_t len = CRYPTO_EC_plen(grp);
++	size_t prime_len = CRYPTO_EC_plen(grp);
++	size_t output_len = prime_len;
++	u8 output_offset = 0;
++	u8 buf[256];
++
+   #ifdef MBEDTLS_ECP_MONTGOMERY_ENABLED
+ 	/* len */
+   #endif
+   #ifdef MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED
+-	if (mbedtls_ecp_get_type(grp) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS)
+-		len = inc_y ? len*2+1 : len+1;
++	if (mbedtls_ecp_get_type(grp) == MBEDTLS_ECP_TYPE_SHORT_WEIERSTRASS) {
++		output_len = inc_y ? prime_len * 2 + 1 : prime_len + 1;
++		output_offset = 1;
++	}
+   #endif
+-	struct wpabuf *buf = wpabuf_alloc(len);
+-	if (buf == NULL)
++
++	if (output_len > sizeof(buf))
+ 		return NULL;
++
+ 	inc_y = inc_y ? MBEDTLS_ECP_PF_UNCOMPRESSED : MBEDTLS_ECP_PF_COMPRESSED;
+-	if (mbedtls_ecp_point_write_binary(grp, &ecdh->Q, inc_y, &len,
+-	                                   wpabuf_mhead_u8(buf), len) == 0) {
+-		wpabuf_put(buf, len);
+-		return buf;
++	if (mbedtls_ecp_point_write_binary(grp, &ecdh->Q, inc_y, &output_len,
++	                                   buf, output_len) == 0) {
++		return wpabuf_alloc_copy(buf + output_offset, output_len - output_offset);
+ 	}
+ 
+-	wpabuf_free(buf);
+ 	return NULL;
+ }
+ 
+@@ -2379,10 +2384,7 @@ struct wpabuf * crypto_ecdh_set_peerkey(
+ 				os_memcpy(buf+2, key, len);
+ 			}
+ 			len >>= 1; /*(repurpose len to prime_len)*/
+-		}
+-		else if (key[0] == 0x02 || key[0] == 0x03) { /* (inc_y == 0) */
+-			--len; /*(repurpose len to prime_len)*/
+-
++		} else { /* (inc_y == 0) */
+ 			/* mbedtls_ecp_point_read_binary() does not currently support
+ 			 * MBEDTLS_ECP_PF_COMPRESSED format (buf[1] = 0x02 or 0x03)
+ 			 * (returns MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE) */
+@@ -2390,22 +2392,21 @@ struct wpabuf * crypto_ecdh_set_peerkey(
+ 			/* derive y, amend buf[] with y for UNCOMPRESSED format */
+ 			if (sizeof(buf)-2 < len*2 || len == 0)
+ 				return NULL;
++
+ 			buf[0] = (u8)(1+len*2);
+ 			buf[1] = 0x04;
++			os_memcpy(buf+2, key, len);
++
+ 			mbedtls_mpi bn;
+ 			mbedtls_mpi_init(&bn);
+-			int ret = mbedtls_mpi_read_binary(&bn, key+1, len)
+-			       || crypto_mbedtls_short_weierstrass_derive_y(grp, &bn,
+-			                                                    key[0] & 1)
++			int ret = mbedtls_mpi_read_binary(&bn, key, len)
++			       || crypto_mbedtls_short_weierstrass_derive_y(grp, &bn, 0)
+ 			       || mbedtls_mpi_write_binary(&bn, buf+2+len, len);
+ 			mbedtls_mpi_free(&bn);
+ 			if (ret != 0)
+ 				return NULL;
+ 		}
+ 
+-		if (key[0] == 0) /*(repurpose len to prime_len)*/
+-			len = CRYPTO_EC_plen(grp);
+-
+ 		if (mbedtls_ecdh_read_public(&ecdh->ctx, buf, buf[0]+1))
+ 			return NULL;
+ 	}