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Diffstat (limited to 'common/tlv.c')
| -rw-r--r-- | common/tlv.c | 309 |
1 files changed, 309 insertions, 0 deletions
diff --git a/common/tlv.c b/common/tlv.c new file mode 100644 index 0000000..9618d04 --- /dev/null +++ b/common/tlv.c @@ -0,0 +1,309 @@ +/* tlv.c - Tag-Length-Value Utilities + * Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc. + * + * This file is part of GnuPG. + * + * This file is free software; you can redistribute it and/or modify + * it under the terms of either + * + * - the GNU Lesser General Public License as published by the Free + * Software Foundation; either version 3 of the License, or (at + * your option) any later version. + * + * or + * + * - the GNU General Public License as published by the Free + * Software Foundation; either version 2 of the License, or (at + * your option) any later version. + * + * or both in parallel, as here. + * + * This file is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, see <https://www.gnu.org/licenses/>. + */ + +#include <config.h> + +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <gpg-error.h> + + +#include "util.h" +#include "tlv.h" + + +static const unsigned char * +do_find_tlv (const unsigned char *buffer, size_t length, + int tag, size_t *nbytes, int nestlevel) +{ + const unsigned char *s = buffer; + size_t n = length; + size_t len; + int this_tag; + int composite; + + for (;;) + { + if (n < 2) + return NULL; /* Buffer definitely too short for tag and length. */ + if (!*s || *s == 0xff) + { /* Skip optional filler between TLV objects. */ + s++; + n--; + continue; + } + composite = !!(*s & 0x20); + if ((*s & 0x1f) == 0x1f) + { /* more tag bytes to follow */ + s++; + n--; + if (n < 2) + return NULL; /* buffer definitely too short for tag and length. */ + if ((*s & 0x1f) == 0x1f) + return NULL; /* We support only up to 2 bytes. */ + this_tag = (s[-1] << 8) | (s[0] & 0x7f); + } + else + this_tag = s[0]; + len = s[1]; + s += 2; n -= 2; + if (len < 0x80) + ; + else if (len == 0x81) + { /* One byte length follows. */ + if (!n) + return NULL; /* we expected 1 more bytes with the length. */ + len = s[0]; + s++; n--; + } + else if (len == 0x82) + { /* Two byte length follows. */ + if (n < 2) + return NULL; /* We expected 2 more bytes with the length. */ + len = ((size_t)s[0] << 8) | s[1]; + s += 2; n -= 2; + } + else + return NULL; /* APDU limit is 65535, thus it does not make + sense to assume longer length fields. */ + + if (composite && nestlevel < 100) + { /* Dive into this composite DO after checking for a too deep + nesting. */ + const unsigned char *tmp_s; + size_t tmp_len; + + tmp_s = do_find_tlv (s, len, tag, &tmp_len, nestlevel+1); + if (tmp_s) + { + *nbytes = tmp_len; + return tmp_s; + } + } + + if (this_tag == tag) + { + *nbytes = len; + return s; + } + if (len > n) + return NULL; /* Buffer too short to skip to the next tag. */ + s += len; n -= len; + } +} + + +/* Locate a TLV encoded data object in BUFFER of LENGTH and + return a pointer to value as well as its length in NBYTES. Return + NULL if it was not found or if the object does not fit into the buffer. */ +const unsigned char * +find_tlv (const unsigned char *buffer, size_t length, + int tag, size_t *nbytes) +{ + const unsigned char *p; + + p = do_find_tlv (buffer, length, tag, nbytes, 0); + if (p && *nbytes > (length - (p-buffer))) + p = NULL; /* Object longer than buffer. */ + return p; +} + + + +/* Locate a TLV encoded data object in BUFFER of LENGTH and + return a pointer to value as well as its length in NBYTES. Return + NULL if it was not found. Note, that the function does not check + whether the value fits into the provided buffer. */ +const unsigned char * +find_tlv_unchecked (const unsigned char *buffer, size_t length, + int tag, size_t *nbytes) +{ + return do_find_tlv (buffer, length, tag, nbytes, 0); +} + + +/* ASN.1 BER parser: Parse BUFFER of length SIZE and return the tag + and the length part from the TLV triplet. Update BUFFER and SIZE + on success. */ +gpg_error_t +parse_ber_header (unsigned char const **buffer, size_t *size, + int *r_class, int *r_tag, + int *r_constructed, int *r_ndef, + size_t *r_length, size_t *r_nhdr) +{ + int c; + unsigned long tag; + const unsigned char *buf = *buffer; + size_t length = *size; + + *r_ndef = 0; + *r_length = 0; + *r_nhdr = 0; + + /* Get the tag. */ + if (!length) + return gpg_err_make (default_errsource, GPG_ERR_EOF); + c = *buf++; length--; ++*r_nhdr; + + *r_class = (c & 0xc0) >> 6; + *r_constructed = !!(c & 0x20); + tag = c & 0x1f; + + if (tag == 0x1f) + { + tag = 0; + do + { + tag <<= 7; + if (!length) + return gpg_err_make (default_errsource, GPG_ERR_EOF); + c = *buf++; length--; ++*r_nhdr; + tag |= c & 0x7f; + + } + while (c & 0x80); + } + *r_tag = tag; + + /* Get the length. */ + if (!length) + return gpg_err_make (default_errsource, GPG_ERR_EOF); + c = *buf++; length--; ++*r_nhdr; + + if ( !(c & 0x80) ) + *r_length = c; + else if (c == 0x80) + *r_ndef = 1; + else if (c == 0xff) + return gpg_err_make (default_errsource, GPG_ERR_BAD_BER); + else + { + unsigned long len = 0; + int count = (c & 0x7f); + + if (count > (sizeof(len)<sizeof(size_t)?sizeof(len):sizeof(size_t))) + return gpg_err_make (default_errsource, GPG_ERR_BAD_BER); + + for (; count; count--) + { + len <<= 8; + if (!length) + return gpg_err_make (default_errsource, GPG_ERR_EOF); + c = *buf++; length--; ++*r_nhdr; + len |= c & 0xff; + } + *r_length = len; + } + + if (*r_length > *r_nhdr && (*r_nhdr + *r_length) < *r_length) + { + return gpg_err_make (default_errsource, GPG_ERR_EOVERFLOW); + } + + /* Without this kludge some example certs can't be parsed. */ + if (*r_class == CLASS_UNIVERSAL && !*r_tag) + *r_length = 0; + + *buffer = buf; + *size = length; + return 0; +} + + +/* FIXME: The following function should not go into this file but for + now it is easier to keep it here. */ + +/* Return the next token of an canonical encoded S-expression. BUF + is the pointer to the S-expression and BUFLEN is a pointer to the + length of this S-expression (used to validate the syntax). Both + are updated to reflect the new position. The token itself is + returned as a pointer into the original buffer at TOK and TOKLEN. + If a parentheses is the next token, TOK will be set to NULL. + TOKLEN is checked to be within the bounds. On error an error code + is returned and pointers are not guaranteed to point to + meaningful values. DEPTH should be initialized to 0 and will + reflect on return the actual depth of the tree. To detect the end + of the S-expression it is advisable to check DEPTH after a + successful return. + + depth = 0; + while (!(err = parse_sexp (&buf, &buflen, &depth, &tok, &toklen)) + && depth) + process_token (tok, toklen); + if (err) + handle_error (); + */ +gpg_error_t +parse_sexp (unsigned char const **buf, size_t *buflen, + int *depth, unsigned char const **tok, size_t *toklen) +{ + const unsigned char *s; + size_t n, vlen; + + s = *buf; + n = *buflen; + *tok = NULL; + *toklen = 0; + if (!n) + return *depth ? gpg_err_make (default_errsource, GPG_ERR_INV_SEXP) : 0; + if (*s == '(') + { + s++; n--; + (*depth)++; + *buf = s; + *buflen = n; + return 0; + } + if (*s == ')') + { + if (!*depth) + return gpg_err_make (default_errsource, GPG_ERR_INV_SEXP); + *toklen = 1; + s++; n--; + (*depth)--; + *buf = s; + *buflen = n; + return 0; + } + for (vlen=0; n && *s && *s != ':' && (*s >= '0' && *s <= '9'); s++, n--) + vlen = vlen*10 + (*s - '0'); + if (!n || *s != ':') + return gpg_err_make (default_errsource, GPG_ERR_INV_SEXP); + s++; n--; + if (vlen > n) + return gpg_err_make (default_errsource, GPG_ERR_INV_SEXP); + *tok = s; + *toklen = vlen; + s += vlen; + n -= vlen; + *buf = s; + *buflen = n; + return 0; +} |