From 45bffde06d55be8341ae2ab97fd9f6d173eea785 Mon Sep 17 00:00:00 2001 From: jsing <> Date: Sat, 25 Dec 2021 07:04:03 +0000 Subject: Rewrite ASN.1 identifier/length parsing in CBS. Provide internal asn1_get_identifier_cbs() and asn1_get_length_cbs() functions that are called from asn1_get_object_cbs(). Convert the existing ASN1_get_object() function so that it calls asn1_get_object_cbs(), before mapping the result into the API that it implements. ok tb@ --- src/lib/libcrypto/asn1/asn1_lib.c | 171 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 171 insertions(+) create mode 100644 src/lib/libcrypto/asn1/asn1_lib.c (limited to 'src/lib/libcrypto/asn1/asn1_lib.c') diff --git a/src/lib/libcrypto/asn1/asn1_lib.c b/src/lib/libcrypto/asn1/asn1_lib.c new file mode 100644 index 0000000000..542a72f6f1 --- /dev/null +++ b/src/lib/libcrypto/asn1/asn1_lib.c @@ -0,0 +1,171 @@ +/* $OpenBSD: asn1_lib.c,v 1.51 2021/12/25 07:04:03 jsing Exp $ */ +/* + * Copyright (c) 2021 Joel Sing + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ + +#include + +#include "bytestring.h" + +static int +asn1_get_identifier_cbs(CBS *cbs, int der_mode, uint8_t *out_class, + int *out_constructed, uint32_t *out_tag_number) +{ + uint8_t tag_class, tag_val; + int tag_constructed; + uint32_t tag_number; + + /* + * Decode ASN.1 identifier octets - see ITU-T X.690 section 8.1.2. + */ + + *out_class = 0; + *out_constructed = 0; + *out_tag_number = 0; + + if (!CBS_get_u8(cbs, &tag_val)) + return 0; + + /* + * ASN.1 tag class, encoding (primitive or constructed) and tag number + * are encoded in one or more identifier octets - the first octet + * contains the 2 bit tag class, the 1 bit encoding type and 5 bits + * of tag number. + * + * For tag numbers larger than 30 (0x1e) the 5 bit tag number in the + * first octet is set to all ones (0x1f) - the tag number is then + * encoded in subsequent octets - each of which have a one bit + * continuation flag and 7 bits of tag number in big-endian form. + * The encoding should not contain leading zeros but can for BER. + */ + tag_class = (tag_val >> 6) & 0x3; + tag_constructed = (tag_val >> 5) & 0x1; + tag_number = tag_val & 0x1f; + + /* Long form. */ + if (tag_number == 0x1f) { + tag_number = 0; + do { + if (!CBS_get_u8(cbs, &tag_val)) + return 0; + if (der_mode && tag_number == 0 && tag_val == 0x80) + return 0; + if (tag_number > (UINT32_MAX >> 7)) + return 0; + tag_number = tag_number << 7 | (tag_val & 0x7f); + } while ((tag_val & 0x80) != 0); + } + + *out_class = tag_class; + *out_constructed = tag_constructed; + *out_tag_number = tag_number; + + return 1; +} + +static int +asn1_get_length_cbs(CBS *cbs, int der_mode, int *out_indefinite, + uint32_t *out_length) +{ + uint8_t len_bytes; + uint32_t length; + uint8_t val; + + /* + * Decode ASN.1 length octets - see ITU-T X.690 section 8.1.3. + */ + + *out_length = 0; + *out_indefinite = 0; + + if (!CBS_get_u8(cbs, &val)) + return 0; + + /* + * Short form - length is encoded in the lower 7 bits of a single byte. + */ + if (val < 0x80) { + *out_length = val; + return 1; + } + + /* + * Indefinite length - content continues until an End of Content (EOC) + * marker is reached. Must be used with constructed encoding. + */ + if (val == 0x80) { + *out_indefinite = 1; + return 1; + } + + /* + * Long form - the lower 7 bits of the first byte specifies the number + * of bytes used to encode the length, the following bytes specify the + * length in big-endian form. The encoding should not contain leading + * zeros but can for BER. A length value of 0x7f is invalid. + */ + if ((len_bytes = val & 0x7f) == 0x7f) + return 0; + + length = 0; + + while (len_bytes-- > 0) { + if (!CBS_get_u8(cbs, &val)) + return 0; + if (der_mode && length == 0 && val == 0) + return 0; + if (length > (UINT32_MAX >> 8)) + return 0; + length = (length << 8) | val; + } + + *out_length = length; + + return 1; +} + +int +asn1_get_object_cbs(CBS *cbs, int der_mode, uint8_t *out_tag_class, + int *out_constructed, uint32_t *out_tag_number, int *out_indefinite, + uint32_t *out_length) +{ + int constructed, indefinite; + uint32_t tag_number, length; + uint8_t tag_class; + + *out_tag_class = 0; + *out_constructed = 0; + *out_tag_number = 0; + *out_indefinite = 0; + *out_length = 0; + + if (!asn1_get_identifier_cbs(cbs, der_mode, &tag_class, &constructed, + &tag_number)) + return 0; + if (!asn1_get_length_cbs(cbs, der_mode, &indefinite, &length)) + return 0; + + /* Indefinite length can only be used with constructed encoding. */ + if (indefinite && !constructed) + return 0; + + *out_tag_class = tag_class; + *out_constructed = constructed; + *out_tag_number = tag_number; + *out_indefinite = indefinite; + *out_length = length; + + return 1; +} -- cgit v1.2.3-55-g6feb