From 786b6a45fbecc068d0fb8b05252a9228e0661c63 Mon Sep 17 00:00:00 2001
From: Andy Polyakov
Date: Sat, 15 Apr 2017 15:53:50 +0200
Subject: [PATCH] asn1/a_int.c: clean up asn1_get_int64.
Trouble was that integer negation wasn't producing *formally* correct
result in platformneutral sense. Formally correct thing to do is
(int64_t)u, but this triggers undefined behaviour for one value that
would still be representable in ASN.1. The trigger was masked with
(int64_t)(0u), but this is formally inappropriate for values other
than the problematic one. [Also reorder branches to favour mostlikely
paths and harmonize asn1_string_set_int64 with asn1_get_int64].]
Reviewedby: Rich Salz
(Merged from https://github.com/openssl/openssl/pull/3231)

crypto/asn1/a_int.c  29 ++++++++++++++++++++
1 file changed, 20 insertions(+), 9 deletions()
diff git a/crypto/asn1/a_int.c b/crypto/asn1/a_int.c
index fe700b22f7..e154343925 100644
 a/crypto/asn1/a_int.c
+++ b/crypto/asn1/a_int.c
@@ 229,12 +229,10 @@ static size_t asn1_put_uint64(unsigned char b[sizeof(uint64_t)], uint64_t r)
}
/*
 * Absolute value of INT64_MIN: we can't just use INT64_MIN as it produces
+ * Absolute value of INT64_MIN: we can't just use INT64_MIN as gcc produces
* overflow warnings.
*/

#define ABS_INT64_MIN \
 ((uint64_t)INT64_MAX + (uint64_t)((INT64_MIN + INT64_MAX)))
+#define ABS_INT64_MIN ((uint64_t)INT64_MAX + ((INT64_MIN + INT64_MAX)))
/* signed version of asn1_get_uint64 */
static int asn1_get_int64(int64_t *pr, const unsigned char *b, size_t blen,
@@ 244,17 +242,25 @@ static int asn1_get_int64(int64_t *pr, const unsigned char *b, size_t blen,
if (asn1_get_uint64(&r, b, blen) == 0)
return 0;
if (neg) {
 if (r > ABS_INT64_MIN) {
+ if (r <= INT64_MAX) {
+ /* Most significant bit is guaranteed to be clear, negation
+ * is guaranteed to be meaningful in platformneutral sense. */
+ *pr = (int64_t)r;
+ } else if (r == ABS_INT64_MIN) {
+ /* This never happens if INT64_MAX == ABS_INT64_MIN, e.g.
+ * on ones'complement system. */
+ *pr = (int64_t)(0  r);
+ } else {
ASN1err(ASN1_F_ASN1_GET_INT64, ASN1_R_TOO_SMALL);
return 0;
}
 *pr = 0  (uint64_t)r;
} else {
 if (r > INT64_MAX) {
+ if (r <= INT64_MAX) {
+ *pr = (int64_t)r;
+ } else {
ASN1err(ASN1_F_ASN1_GET_INT64, ASN1_R_TOO_LARGE);
return 0;
}
 *pr = (int64_t)r;
}
return 1;
}
@@ 319,7 +325,12 @@ static int asn1_string_set_int64(ASN1_STRING *a, int64_t r, int itype)
a>type = itype;
if (r < 0) {
 off = asn1_put_uint64(tbuf, r);
+ /* Most obvious 'r' triggers undefined behaviour for most
+ * common INT64_MIN. Even though below '0  (uint64_t)r' can
+ * appear two'scomplement centric, it does produce correct/
+ * expected result even on one'scomplement. This is because
+ * cast to unsigned has to change bit pattern... */
+ off = asn1_put_uint64(tbuf, 0  (uint64_t)r);
a>type = V_ASN1_NEG;
} else {
off = asn1_put_uint64(tbuf, r);

2.34.1