parse supported groups into a buffer

goatgoose · Sep 19, 2023 · 201852c · 201852c
1 parent b4f0c5c
commit 201852c
Showing 1 changed file with 42 additions and 10 deletions.
diff --git a/tls/extensions/s2n_client_supported_groups.c b/tls/extensions/s2n_client_supported_groups.c
@@ -26,6 +26,8 @@
 #include "tls/s2n_tls_parameters.h"
 #include "utils/s2n_safety.h"
 
+#define S2N_MAX_RECEIVED_SUPPORTED_GROUPS 64
+
 static int s2n_client_supported_groups_send(struct s2n_connection *conn, struct s2n_stuffer *out);
 static int s2n_client_supported_groups_recv(struct s2n_connection *conn, struct s2n_stuffer *extension);
 
@@ -78,6 +80,40 @@ static int s2n_client_supported_groups_send(struct s2n_connection *conn, struct
     return S2N_SUCCESS;
 }
 
+static S2N_RESULT s2n_client_supported_groups_validate_list_size(struct s2n_stuffer *extension, uint16_t list_size)
+{
+    RESULT_ENSURE_LTE(list_size, s2n_stuffer_data_available(extension));
+    RESULT_ENSURE_EQ(list_size % sizeof(uint16_t), 0);
+    return S2N_RESULT_OK;
+}
+
+S2N_RESULT s2n_client_supported_groups_parse(struct s2n_stuffer *extension, uint16_t *supported_groups_list,
+        uint16_t supported_groups_list_len, uint16_t *supported_groups_count_out)
+{
+    RESULT_ENSURE_REF(supported_groups_count_out);
+    *supported_groups_count_out = 0;
+
+    RESULT_ENSURE_REF(extension);
+    RESULT_ENSURE_REF(supported_groups_list);
+
+    uint16_t supported_groups_list_size = 0;
+    RESULT_GUARD_POSIX(s2n_stuffer_read_uint16(extension, &supported_groups_list_size));
+    if (s2n_result_is_error(s2n_client_supported_groups_validate_list_size(extension, supported_groups_list_size))) {
+        /* Malformed length, ignore the extension */
+        return S2N_RESULT_OK;
+    }
+
+    uint16_t supported_groups_count = supported_groups_list_size / 2;
+    RESULT_ENSURE_LTE(supported_groups_count, supported_groups_list_len);
+    *supported_groups_count_out = supported_groups_count;
+
+    for (size_t i = 0; i < supported_groups_count; i++) {
+        RESULT_GUARD_POSIX(s2n_stuffer_read_uint16(extension, &supported_groups_list[i]));
+    }
+
+    return S2N_RESULT_OK;
+}
+
 /* Populates the appropriate index of either the mutually_supported_curves or
  * mutually_supported_kem_groups array based on the received IANA ID. Will
  * ignore unrecognized IANA IDs (and return success). */
@@ -165,17 +201,13 @@ static int s2n_client_supported_groups_recv(struct s2n_connection *conn, struct
     POSIX_ENSURE_REF(conn);
     POSIX_ENSURE_REF(extension);
 
-    uint16_t size_of_all;
-    POSIX_GUARD(s2n_stuffer_read_uint16(extension, &size_of_all));
-    if (size_of_all > s2n_stuffer_data_available(extension) || (size_of_all % sizeof(uint16_t))) {
-        /* Malformed length, ignore the extension */
-        return S2N_SUCCESS;
-    }
+    uint16_t supported_groups[S2N_MAX_RECEIVED_SUPPORTED_GROUPS] = { 0 };
+    uint16_t supported_groups_count = 0;
+    POSIX_GUARD_RESULT(s2n_client_supported_groups_parse(extension, supported_groups, S2N_MAX_RECEIVED_SUPPORTED_GROUPS,
+            &supported_groups_count));
 
-    for (size_t i = 0; i < (size_of_all / sizeof(uint16_t)); i++) {
-        uint16_t iana_id;
-        POSIX_GUARD(s2n_stuffer_read_uint16(extension, &iana_id));
-        POSIX_GUARD(s2n_client_supported_groups_recv_iana_id(conn, iana_id));
+    for (size_t i = 0; i < supported_groups_count; i++) {
+        POSIX_GUARD(s2n_client_supported_groups_recv_iana_id(conn, supported_groups[i]));
     }
 
     POSIX_GUARD(s2n_choose_supported_group(conn));