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Fix BN_mod_word bug.

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On systems where we do not have BN_ULLONG (notably Win64), BN_mod_word() can
return incorrect results if the supplied modulus is too big.

(Imported from upstream's e82fd1b4574c8908b2c3bb68e1237f057a981820 and
e4c4b2766bb97b34ea3479252276ab7c66311809.)

Change-Id: Icee8a7c5c67a8ee14c276097f43a7c491e68c2f9
Reviewed-on: https://boringssl-review.googlesource.com/8233
Reviewed-by: Adam Langley <agl@google.com>
This commit is contained in:
David Benjamin 2016-06-09 18:57:56 +00:00 committed by Adam Langley
parent 8f1e113a73
commit 67cb49d045
2 changed files with 20 additions and 0 deletions
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6
crypto/bn/bn_test.cc
View File

@ -850,11 +850,17 @@ static bool test_div_word(FILE *fp) {
return false;
}
BN_ULONG s = b->d[0];
BN_ULONG rmod = BN_mod_word(b.get(), s);
BN_ULONG r = BN_div_word(b.get(), s);
if (r == (BN_ULONG)-1) {
return false;
}
if (rmod != r) {
fprintf(stderr, "Mod (word) test failed!\n");
return false;
}
if (fp != NULL) {
BN_print_fp(fp, a.get());
puts_fp(fp, " / ");

14
crypto/bn/div.c
View File

@ -644,6 +644,20 @@ BN_ULONG BN_mod_word(const BIGNUM *a, BN_ULONG w) {
return (BN_ULONG) -1;
}
#ifndef BN_ULLONG
/* If |w| is too long and we don't have |BN_ULLONG| then we need to fall back
* to using |BN_div_word|. */
if (w > ((BN_ULONG)1 << BN_BITS4)) {
BIGNUM *tmp = BN_dup(a);
if (tmp == NULL) {
return (BN_ULONG)-1;
}
ret = BN_div_word(tmp, w);
BN_free(tmp);
return ret;
}
#endif
w &= BN_MASK2;
for (i = a->top - 1; i >= 0; i--) {
#ifndef BN_ULLONG