tls: send EMPTY_RENEGOTIATION_INFO_SCSV in our client hello

Hoped this can make cdn.kernel.org to like us more. Nope.
While at it, made error reporting more useful.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 86 insertions, 26 deletions

diff --git a/networking/tls.c b/networking/tls.c
index 89f2ec603..4456c7d26 100644
--- a/networking/tls.c
+++ b/networking/tls.c
@@ -22,6 +22,16 @@
 #define TLS_DEBUG_HASH 0
 #define TLS_DEBUG_DER  0
 #define TLS_DEBUG_FIXED_SECRETS 0
+#if 0
+# define dump_raw_out(...) dump_hex(__VA_ARGS__)
+#else
+# define dump_raw_out(...) ((void)0)
+#endif
+#if 0
+# define dump_raw_in(...) dump_hex(__VA_ARGS__)
+#else
+# define dump_raw_in(...) ((void)0)
+#endif
 
 #if TLS_DEBUG
 # define dbg(...) fprintf(stderr, __VA_ARGS__)
@@ -35,18 +45,6 @@
 # define dbg_der(...) ((void)0)
 #endif
 
-#if 0
-# define dump_raw_out(...) dump_hex(__VA_ARGS__)
-#else
-# define dump_raw_out(...) ((void)0)
-#endif
-
-#if 0
-# define dump_raw_in(...) dump_hex(__VA_ARGS__)
-#else
-# define dump_raw_in(...) ((void)0)
-#endif
-
 #define RECORD_TYPE_CHANGE_CIPHER_SPEC  20
 #define RECORD_TYPE_ALERT               21
 #define RECORD_TYPE_HANDSHAKE           22
@@ -154,8 +152,18 @@
 // works against "openssl s_server -cipher NULL"
 // and against wolfssl-3.9.10-stable/examples/server/server.c:
 //#define CIPHER_ID TLS_RSA_WITH_NULL_SHA256 // for testing (does everything except encrypting)
+
 // works against wolfssl-3.9.10-stable/examples/server/server.c
-#define CIPHER_ID TLS_RSA_WITH_AES_256_CBC_SHA256 // ok, no SERVER_KEY_EXCHANGE
+// works for kernel.org
+// does not work for cdn.kernel.org (e.g. downloading an actual tarball, not a web page)
+//  getting alert 40 "handshake failure" at once
+//  with GNU Wget 1.18, they agree on TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (0xC02F) cipher
+//  fail: openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -no_tls1 -no_tls1_1 -cipher AES256-SHA256
+//  fail: openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -no_tls1 -no_tls1_1 -cipher AES256-GCM-SHA384
+//  fail: openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -no_tls1 -no_tls1_1 -cipher AES128-SHA256
+//  ok:   openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -no_tls1 -no_tls1_1 -cipher AES128-GCM-SHA256
+//  ok:   openssl s_client -connect cdn.kernel.org:443 -debug -tls1_2 -no_tls1 -no_tls1_1 -cipher AES128-SHA
+#define CIPHER_ID TLS_RSA_WITH_AES_256_CBC_SHA256 // no SERVER_KEY_EXCHANGE from peer
 
 enum {
         RSA_PREMASTER_SIZE = 48,
@@ -445,6 +453,18 @@ static void prf_hmac_sha256(
 #undef SEED
 }
 
+static void bad_record_die(tls_state_t *tls, const char *expected, int len)
+{
+        bb_error_msg_and_die("got bad TLS record (len:%d) while expecting %s", len, expected);
+        if (len > 0) {
+                uint8_t *p = tls->inbuf;
+                while (len > 0)
+                        fprintf(stderr, " %02x", *p++);
+                fputc('\n', stderr);
+        }
+        xfunc_die();
+}
+
 static void tls_error_die(tls_state_t *tls)
 {
         dump_tls_record(tls->inbuf, tls->ofs_to_buffered + tls->buffered_size);
@@ -671,6 +691,18 @@ static int tls_has_buffered_record(tls_state_t *tls)
         return rec_size;
 }
 
+static const char *alert_text(int code)
+{
+        switch (code) {
+        case 20:  return "bad MAC";
+        case 50:  return "decode error";
+        case 51:  return "decrypt error";
+        case 40:  return "handshake failure";
+        case 112: return "unrecognized name";
+        }
+        return itoa(code);
+}
+
 static int tls_xread_record(tls_state_t *tls)
 {
         struct record_hdr *xhdr;
@@ -780,16 +812,28 @@ static int tls_xread_record(tls_state_t *tls)
         if (xhdr->type == RECORD_TYPE_ALERT && sz >= 2) {
                 uint8_t *p = tls->inbuf + RECHDR_LEN;
                 dbg("ALERT size:%d level:%d description:%d\n", sz, p[0], p[1]);
+                if (p[0] == 2) { /* fatal */
+                        bb_error_msg_and_die("TLS %s from peer (alert code %d): %s",
+                                "error",
+                                p[1], alert_text(p[1])
+                        );
+                }
                 if (p[0] == 1) { /* warning */
                         if (p[1] == 0) { /* "close_notify" warning: it's EOF */
                                 dbg("EOF (TLS encoded) from peer\n");
                                 sz = 0;
                                 goto end;
                         }
+//This possibly needs to be cached and shown only if
+//a fatal alert follows
+//                      bb_error_msg("TLS %s from peer (alert code %d): %s",
+//                              "warning",
+//                              p[1], alert_text(p[1])
+//                      );
                         /* discard it, get next record */
                         goto again;
                 }
-                /* p[0] == 1: fatal error, others: not defined in protocol */
+                /* p[0] not 1 or 2: not defined in protocol */
                 sz = 0;
                 goto end;
         }
@@ -1031,7 +1075,7 @@ static int tls_xread_handshake_block(tls_state_t *tls, int min_len)
          || xhdr->proto_maj != TLS_MAJ
          || xhdr->proto_min != TLS_MIN
         ) {
-                tls_error_die(tls);
+                bad_record_die(tls, "handshake record", len);
         }
         dbg("got HANDSHAKE\n");
         return len;
@@ -1051,7 +1095,6 @@ static ALWAYS_INLINE void fill_handshake_record_hdr(void *buf, unsigned type, un
         h->len24_lo  = len & 0xff;
 }
 
-//TODO: implement RFC 5746 (Renegotiation Indication Extension) - some servers will refuse to work with us otherwise
 static void send_client_hello(tls_state_t *tls, const char *sni)
 {
         struct client_hello {
@@ -1062,18 +1105,27 @@ static void send_client_hello(tls_state_t *tls, const char *sni)
                 uint8_t session_id_len;
                 /* uint8_t session_id[]; */
                 uint8_t cipherid_len16_hi, cipherid_len16_lo;
-                uint8_t cipherid[2 * 1]; /* actually variable */
+                uint8_t cipherid[2 * 2]; /* actually variable */
                 uint8_t comprtypes_len;
                 uint8_t comprtypes[1]; /* actually variable */
                 /* Extensions (SNI shown):
                  * hi,lo // len of all extensions
-                 *   0x00,0x00 // extension_type: "Server Name"
-                 *   0x00,0x0e // list len (there can be more than one SNI)
-                 *     0x00,0x0c // len of 1st Server Name Indication
-                 *       0x00    // name type: host_name
-                 *       0x00,0x09   // name len
+                 *   00,00 // extension_type: "Server Name"
+                 *   00,0e // list len (there can be more than one SNI)
+                 *     00,0c // len of 1st Server Name Indication
+                 *       00    // name type: host_name
+                 *       00,09   // name len
                  *       "localhost" // name
                  */
+// GNU Wget 1.18 to cdn.kernel.org sends these extensions:
+// 0055
+//   0005 0005 0100000000 - status_request
+//   0000 0013 0011 00 000e 63646e 2e 6b65726e656c 2e 6f7267 - server_name
+//   ff01 0001 00 - renegotiation_info
+//   0023 0000 - session_ticket
+//   000a 0008 0006001700180019 - supported_groups
+//   000b 0002 0100 - ec_point_formats
+//   000d 0016 00140401040305010503060106030301030302010203 - signature_algorithms
         };
         struct client_hello *record;
         int len;
@@ -1084,6 +1136,7 @@ static void send_client_hello(tls_state_t *tls, const char *sni)
                 len += 11 + strlen(sni);
         record = tls_get_outbuf(tls, len);
         memset(record, 0, len);
+
         fill_handshake_record_hdr(record, HANDSHAKE_CLIENT_HELLO, len);
         record->proto_maj = TLS_MAJ;    /* the "requested" version of the protocol, */
         record->proto_min = TLS_MIN;    /* can be higher than one in record headers */
@@ -1092,10 +1145,16 @@ static void send_client_hello(tls_state_t *tls, const char *sni)
                 memset(record->rand32, 0x11, sizeof(record->rand32));
         memcpy(tls->hsd->client_and_server_rand32, record->rand32, sizeof(record->rand32));
         /* record->session_id_len = 0; - already is */
+
         /* record->cipherid_len16_hi = 0; */
-        record->cipherid_len16_lo = 2 * 1;
-        record->cipherid[0] = CIPHER_ID >> 8;
+        record->cipherid_len16_lo = 2 * 2;
+        if ((CIPHER_ID >> 8) != 0)
+                record->cipherid[0] = CIPHER_ID >> 8;
         record->cipherid[1] = CIPHER_ID & 0xff;
+        /* RFC 5746 Renegotiation Indication Extension - some servers will refuse to work with us otherwise */
+        /*record->cipherid[2] = TLS_EMPTY_RENEGOTIATION_INFO_SCSV >> 8; - zero */
+        record->cipherid[3] = TLS_EMPTY_RENEGOTIATION_INFO_SCSV & 0xff;
+
         record->comprtypes_len = 1;
         /* record->comprtypes[0] = 0; */
 
@@ -1136,8 +1195,9 @@ static void get_server_hello(tls_state_t *tls)
 
         struct server_hello *hp;
         uint8_t *cipherid;
+        int len;
 
-        tls_xread_handshake_block(tls, 74);
+        len = tls_xread_handshake_block(tls, 74);
 
         hp = (void*)tls->inbuf;
         // 74 bytes:
@@ -1150,7 +1210,7 @@ static void get_server_hello(tls_state_t *tls)
          || hp->proto_maj != TLS_MAJ
          || hp->proto_min != TLS_MIN
         ) {
-                tls_error_die(tls);
+                bad_record_die(tls, "'server hello'", len);
         }
 
         cipherid = &hp->cipherid_hi;