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asn1/a_int.c: fix "next negative minimum" corner case in c2i_ibuf.

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"Next" refers to negative minimum "next" to one presentable by given
number of bytes. For example, -128 is negative minimum presentable by
one byte, and -256 is "next" one.

Thanks to Kazuki Yamaguchi for report, GH#3339

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
This commit is contained in:
Andy Polyakov 2017-04-28 10:06:35 +02:00
parent 595b2a4237
commit 1e93d619b7
1 changed files with 14 additions and 3 deletions
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17
crypto/asn1/a_int.c
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@ -167,10 +167,21 @@ static size_t c2i_ibuf(unsigned char *b, int *pneg,
}
return 1;
}
if (p[0] == 0 || p[0] == 0xFF)
pad = 0;
if (p[0] == 0) {
pad = 1;
else
pad = 0;
} else if (p[0] == 0xFF) {
size_t i;
/*
* Special case [of "one less minimal negative" for given length]:
* if any other bytes non zero it was padded, otherwise not.
*/
for (pad = 0, i = 1; i < plen; i++)
pad |= p[i];
pad = pad != 0 ? 1 : 0;
}
/* reject illegal padding: first two octets MSB can't match */
if (pad && (neg == (p[1] & 0x80))) {
ASN1err(ASN1_F_C2I_IBUF, ASN1_R_ILLEGAL_PADDING);