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asn1: Fix UB and incorrect codec for unconstrained INTEGER values of -1

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This commit is contained in:
Nicolas Williams
2022-10-26 01:53:10 -05:00
parent 476d216f89
commit e4311f3a82
5 changed files with 206 additions and 55 deletions
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48
lib/asn1/der_get.c
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@@ -86,9 +86,12 @@ der_get_integer (const unsigned char *p, size_t len,
int val = 0;
size_t oldlen = len;
if (len > sizeof(val))
if (len == sizeof(val) + 1 && (p[0] == 0 || p[0] == 0xff))
;
else if (len > sizeof(val))
return ASN1_OVERRUN;
/* We assume we're on a twos-complement platform */
if (len > 0) {
val = (signed char)*p++;
while (--len)
@@ -109,6 +112,7 @@ der_get_integer64 (const unsigned char *p, size_t len,
if (len > sizeof(val))
return ASN1_OVERRUN;
/* We assume we're on a twos-complement platform */
if (len > 0) {
val = (signed char)*p++;
while (--len)
@@ -456,13 +460,45 @@ der_get_heim_integer (const unsigned char *p, size_t len,
if (p[0] & 0x80) {
unsigned char *q;
int carry = 1;
data->negative = 1;
/*
* A negative number. It's going to be a twos complement byte array.
* We're going to leave the positive value in `data->data', but set the
* `data->negative' flag. That means we need to negate the
* twos-complement integer received.
*/
data->negative = 1;
data->length = len;
if (p[0] == 0xff) {
if (data->length == 1) {
/* One byte of all ones == -1 */
q = data->data = malloc(1);
*q = 1;
data->length = 1;
if (size)
*size = 1;
return 0;
}
p++;
data->length--;
/*
* We could check if the next byte's high bit is set, which would
* be an error ("illegal padding" in OpenSSL). However, this would
* mean failing to accept certificates made by certain CAs that
* would read 8 bytes of RNG into a buffer, slap on length 8, then
* slap on the tag [UNIVERSAL INTEGER], and make that the
* serialNumber field's encoding, which then fails to parse in
* around 1 in 256 certificates.
*
* So let's not.
*
* if (p[0] & 0x80)
* return ASN1_PARSE_ERROR; // or a new error code
*/
}
data->data = malloc(data->length);
if (data->data == NULL) {
@@ -471,9 +507,17 @@ der_get_heim_integer (const unsigned char *p, size_t len,
*size = 0;
return ENOMEM;
}
/*
* Note that if `data->length' were zero, this would be UB because we
* underflow if data->length is zero even though we wouldn't actually
* dereference the byte before data->data. Thus we check above for
* that.
*/
q = &((unsigned char*)data->data)[data->length - 1];
p += data->length - 1;
while (q >= (unsigned char*)data->data) {
/* *p XOR 0xff -> ~*p; we're dealing with twos complement */
*q = *p ^ 0xff;
if (carry)
carry = !++*q;