On systems where we do not have BN_ULLONG defined (most 64-bit systems),

BN_mod_word() can return incorrect results if the supplied modulus is
too big, so we need to fall back to BN_div_word.

Now that BN_mod_word may fail, handle errors properly update the man page.

Thanks to Brian Smith for pointing out these fixes from BoringSSL:

https://boringssl.googlesource.com/boringssl/+/67cb49d045f04973ddba0f92fe8a8ad483c7da89
https://boringssl.googlesource.com/boringssl/+/44bedc348d9491e63c7ed1438db100a4b8a830be

ok beck@

1 files changed, 24 insertions, 4 deletions

diff --git a/src/regress/lib/libcrypto/bn/general/bntest.c b/src/regress/lib/libcrypto/bn/general/bntest.c
index c6bd788b54..1d541778e3 100644
--- a/src/regress/lib/libcrypto/bn/general/bntest.c
+++ b/src/regress/lib/libcrypto/bn/general/bntest.c
@@ -514,7 +514,7 @@ int
 test_div_word(BIO *bp)
 {
         BIGNUM   a, b;
-        BN_ULONG r, s;
+        BN_ULONG r, rmod, s;
         int i;
         int rc = 1;
 
@@ -523,14 +523,34 @@ test_div_word(BIO *bp)
 
         for (i = 0; i < num0; i++) {
                 do {
-                        BN_bntest_rand(&a, 512, -1, 0);
-                        BN_bntest_rand(&b, BN_BITS2, -1, 0);
+                        if (!BN_bntest_rand(&a, 512, -1, 0) ||
+                            !BN_bntest_rand(&b, BN_BITS2, -1, 0)) {
+                                rc = 0;
+                                break;
+                        }
                         s = b.d[0];
                 } while (!s);
 
-                BN_copy(&b, &a);
+                if (!BN_copy(&b, &a)) {
+                        rc = 0;
+                        break;
+                }
+
+                s = b.d[0];
+                rmod = BN_mod_word(&b, s);
                 r = BN_div_word(&b, s);
 
+                if (r == (BN_ULONG)-1 || rmod == (BN_ULONG)-1) {
+                        rc = 0;
+                        break;
+                }
+
+                if (rmod != r) {
+                        fprintf(stderr, "Mod (word) test failed!\n");
+                        rc = 0;
+                        break;
+                }
+
                 if (bp != NULL) {
                         if (!results) {
                                 BN_print(bp, &a);