DO NOT MERGE SMP: Validate remote elliptic curve points

Fixes: 72377774
Test: net_test_stack_smp (where applicable)
Change-Id: Iefcf97364493467075fadefd77d12716f71cd4f6
(cherry picked from commit 9181ec28da94705a763edbe60bd2a87e5f882beb)
(cherry picked from commit 4f9ed8f66eb57142f4bedd667230b55bbf8da366)

diff --git a/stack/smp/p_256_ecc_pp.c b/stack/smp/p_256_ecc_pp.c
index 2eaebd4..bbe126d 100644 (file)
--- a/stack/smp/p_256_ecc_pp.c
+++ b/stack/smp/p_256_ecc_pp.c
@@ -259,4 +259,27 @@ void ECC_PointMult_Bin_NAF(Point *q, Point *p, DWORD *n, uint32_t keyLength)
     multiprecision_mersenns_mult_mod(q->y, q->y, q->z, keyLength);
 }
 
-
+bool ECC_ValidatePoint(const Point* pt) {
+    const size_t kl = KEY_LENGTH_DWORDS_P256;
+    p_256_init_curve(kl);
+
+    // Ensure y^2 = x^3 + a*x + b (mod p); a = -3
+
+    // y^2 mod p
+    DWORD y2_mod[kl];
+    memset(y2_mod, 0, sizeof(y2_mod));
+    multiprecision_mersenns_squa_mod(y2_mod, (DWORD*)pt->y, kl);
+
+    // Right hand side calculation
+    DWORD rhs[kl];
+    memset(rhs, 0, sizeof(rhs));
+    multiprecision_mersenns_squa_mod(rhs, (DWORD*)pt->x, kl);
+    DWORD three[kl];
+    memset(three, 0, sizeof(three));
+    three[0] = 3;
+    multiprecision_sub_mod(rhs, rhs, three, kl);
+    multiprecision_mersenns_mult_mod(rhs, rhs, (DWORD*)pt->x, kl);
+    multiprecision_add_mod(rhs, rhs, curve_p256.b, kl);
+
+    return multiprecision_compare(rhs, y2_mod, kl) == 0;
+}

diff --git a/stack/smp/p_256_ecc_pp.h b/stack/smp/p_256_ecc_pp.h
index fd3dc64..27869ba 100644 (file)
--- a/stack/smp/p_256_ecc_pp.h
+++ b/stack/smp/p_256_ecc_pp.h
@@ -24,6 +24,7 @@
 
 #pragma once
 
+#include <stdbool.h>
 #include "p_256_multprecision.h"
 
 typedef unsigned long  DWORD;
@@ -56,6 +57,8 @@ typedef struct {
 extern elliptic_curve_t curve;
 extern elliptic_curve_t curve_p256;
 
+bool ECC_ValidatePoint(const Point* p);
+
 void ECC_PointMult_Bin_NAF(Point *q, Point *p, DWORD *n, uint32_t keyLength);
 
 #define ECC_PointMult(q, p, n, keyLength)  ECC_PointMult_Bin_NAF(q, p, n, keyLength)

diff --git a/stack/smp/smp_act.c b/stack/smp/smp_act.c
index e4152a4..688d967 100644 (file)
--- a/stack/smp/smp_act.c
+++ b/stack/smp/smp_act.c
@@ -16,11 +16,13 @@
  *
  ******************************************************************************/
 
+#include <log/log.h>
 #include <string.h>
 #include "device/include/interop.h"
 #include "include/bt_target.h"
 #include "stack/btm/btm_int.h"
 #include "stack/include/l2c_api.h"
+#include "stack/smp/p_256_ecc_pp.h"
 #include "stack/smp/smp_int.h"
 #include "utils/include/bt_utils.h"
 
@@ -750,6 +752,17 @@ void smp_process_pairing_public_key(tSMP_CB *p_cb, tSMP_INT_DATA *p_data)
 
     STREAM_TO_ARRAY(p_cb->peer_publ_key.x, p, BT_OCTET32_LEN);
     STREAM_TO_ARRAY(p_cb->peer_publ_key.y, p, BT_OCTET32_LEN);
+
+    Point pt;
+    memcpy(pt.x, p_cb->peer_publ_key.x, BT_OCTET32_LEN);
+    memcpy(pt.y, p_cb->peer_publ_key.y, BT_OCTET32_LEN);
+
+    if (!ECC_ValidatePoint(&pt)) {
+        android_errorWriteLog(0x534e4554, "72377774");
+        smp_sm_event(p_cb, SMP_AUTH_CMPL_EVT, &reason);
+        return;
+    }
+
     p_cb->flags |= SMP_PAIR_FLAG_HAVE_PEER_PUBL_KEY;
 
     smp_wait_for_both_public_keys(p_cb, NULL);