Add fix and test for bech32 bad input

Thanks to Christian Reitter and Dr. Jochen Hoenicke for finding the
issue.

Author: jgriffiths

.gitignore

@@ -39,6 +39,7 @@ src/stamp-h1
 src/test/Makefile
 src/test/Makefile.in
 src/wallycore.pc
+src/test_bech32*
 src/test_clear*
 src/test_tx*
 src/test_elements_tx*

CHANGES.md

@@ -2,6 +2,11 @@
 
 ## Version 0.6.5
 
+- Invalid bech32 addresses may have caused an out of bounds read. Thanks to
+  Christian Reitter and Dr. Jochen Hoenicke for finding and reporting this
+  issue. All users are advised to upgrade as soon as possible to minimise
+  any potential impact.
+
 - BIP38_KEY_TESTNET was changed to reflect the testnet network version. BIP38 testnet keys
   created with older versions of wally were not valid for testnet.
 

src/Makefile.am

@@ -194,6 +194,11 @@ SUBDIRS = secp256k1
 TESTS =
 noinst_PROGRAMS =
 if RUN_TESTS
+TESTS += test_bech32
+noinst_PROGRAMS += test_bech32
+test_bech32_SOURCES = ctest/test_bech32.c
+test_bech32_CFLAGS = -I$(top_srcdir)/include $(AM_CFLAGS)
+test_bech32_LDADD = $(lib_LTLIBRARIES) @CTEST_EXTRA_STATIC@
 if USE_PTHREAD
 TESTS += test_clear
 noinst_PROGRAMS += test_clear

src/bech32.c

@@ -99,10 +99,10 @@ static int bech32_decode(char *hrp, uint8_t *data, size_t *data_len, const char
     while (*data_len < input_len && input[(input_len - 1) - *data_len] != '1') {
         ++(*data_len);
     }
-    hrp_len = input_len - (1 + *data_len);
-    if (hrp_len < 1 || *data_len < 6) {
+    if (1 + *data_len >= input_len || *data_len < 6) {
         return 0;
     }
+    hrp_len = input_len - (1 + *data_len);
     *(data_len) -= 6;
     for (i = 0; i < hrp_len; ++i) {
         int ch = input[i];

src/ctest/test_bech32.c

@@ -0,0 +1,37 @@
+#include "config.h"
+
+#include <wally_core.h>
+#include <wally_address.h>
+#include <stdio.h>
+#include <stdbool.h>
+
+static const char *invalid = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefg";
+
+static bool check_segwit_to_bytes()
+{
+    unsigned char *mem = calloc(90, sizeof(unsigned char));
+    size_t written;
+    int ret;
+
+    if (!mem)
+        return false;
+
+    ret = wally_addr_segwit_to_bytes(invalid, "tb", 0, mem, 90, &written);
+
+    if (ret != WALLY_EINVAL)
+        return false;
+
+    return true;
+}
+
+int main(void)
+{
+    bool tests_ok = true;
+
+    if (!check_segwit_to_bytes()) {
+        printf("check_segwit_to_bytes test failed!\n");
+        tests_ok = false;
+    }
+
+    return tests_ok ? 0 : 1;
+}

src/test/test_bech32.py

@@ -66,6 +66,11 @@ def test_segwit_address(self):
             ret, result_script_hex = self.decode(addr, family)
             self.assertEqual(ret, WALLY_EINVAL)
 
+        out, out_len = make_cbuffer('00' * (32 + 2))
+        bad = 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefg'
+        ret, written = wally_addr_segwit_to_bytes(utf8(bad), utf8('tb'), 0, out, out_len)
+        self.assertEqual((ret, written), (WALLY_EINVAL, 0))
+
 
 if __name__ == '__main__':
     unittest.main()

tools/cleanup.sh

@@ -23,6 +23,7 @@ rm -f src/*pyc
 rm -f src/test/*pyc
 rm -f src/config.h.in
 rm -rf src/lcov*
+rm -f src/test_bech32*
 rm -f src/test_clear*
 rm -f src/test_tx*
 rm -f src/test-suite.log