mirror of https://gerrit.osmocom.org/asn1c
236 lines
6.4 KiB
C
236 lines
6.4 KiB
C
/*-
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* Copyright (c) 2003 Lev Walkin <vlm@lionet.info>. All rights reserved.
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* Redistribution and modifications are permitted subject to BSD license.
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*/
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#include <constr_TYPE.h>
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#include <assert.h>
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#define ADVANCE(num_bytes) do { \
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size_t num = num_bytes; \
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ptr += num; \
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size -= num; \
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consumed_myself += num; \
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} while(0)
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#define RETURN(_code) do { \
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ber_dec_rval_t rval; \
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rval.code = _code; \
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rval.consumed = consumed_myself; \
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return rval; \
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} while(0)
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/*
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* The BER decoder of any type.
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*/
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ber_dec_rval_t
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ber_decode(asn1_TYPE_descriptor_t *type_descriptor,
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void **struct_ptr, void *ptr, size_t size) {
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/*
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* Invoke type-specific decoder.
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*/
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return type_descriptor->ber_decoder(type_descriptor,
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struct_ptr, /* Pointer to the destination structure */
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ptr, size, /* Buffer and its size */
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0 /* Default tag mode is 0 */
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);
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}
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/*
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* Check the set of <TL<TL<TL...>>> tags matches the definition.
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*/
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ber_dec_rval_t
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ber_check_tags(asn1_TYPE_descriptor_t *td, ber_dec_ctx_t *ctx,
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void *ptr, size_t size, int tag_mode,
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ber_tlv_len_t *last_length, int *opt_tlv_form) {
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ssize_t consumed_myself = 0;
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ssize_t tag_len;
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ssize_t len_len;
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ber_tlv_tag_t tlv_tag;
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ber_tlv_len_t tlv_len;
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ber_tlv_len_t limit_len = -1;
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int expect_00_terminators = 0;
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int tlv_constr = -1; /* If CHOICE, opt_tlv_form is not given */
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int tagno;
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/*
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* So what does all this tags_impl_skip stuff mean?
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* Imagine two types,
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* A ::= [5] IMPLICIT T
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* B ::= [2] EXPLICIT T
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* Where T is defined as
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* T ::= [4] IMPLICIT SEQUENCE { ... }
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*
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* Let's say, we are starting to decode type A, given the
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* following TLV stream: <5> <0>. What does this mean?
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* It means that the type A contains type T which is,
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* in turn, empty.
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* Remember though, that we are still in A. We cannot
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* just pass control to the type T decoder. Why? Because
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* the type T decoder expects <4> <0>, not <5> <0>.
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* So, we must make sure we are going to receive <5> while
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* still in A, then pass control to the T decoder, indicating
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* that the tag <4> was implicitly skipped. The decoder of T
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* hence will be prepared to treat <4> as valid tag, and decode
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* it appropriately.
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*/
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/*
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* We have a list of tags that must occur in the stream:
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* {A,B,C}
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* However, it may be indicated that the type is
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* implicitly tagged in the caller, so it really boils down to the
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* {I,B,C} or even {I,C}
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* This is because the implicit tag at above structure may replace
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* zero or more (or every) tags which follow it. We don't care
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* about the precise number, as it is already computed for us
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* by the ASN.1 compiler and placed into td->tags_impl_skip.
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* So let's suppose the only tag left after implicit tagging is {I}.
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* Yet, the table we have is {A,B,C} and td->tags_impl_skip=3.
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* We need to check at least one tag in the loop, so the loop range
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* is modified so it will be invoked at least one time.
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*/
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tagno = ctx->step /* Continuing where left previously */
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+ (tag_mode==-1?(td->tags_impl_skip-1):0)
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+ (tag_mode==1?-1:0)
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;
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ASN_DEBUG("ber_check_tags(%s, size=%ld, tm=%d, step=%d, tagno=%d)",
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td->name, (long)size, tag_mode, ctx->step, tagno);
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//assert(td->tags_count >= 1); ?May not be the case for CHOICE!
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assert(tagno < td->tags_count); /* At least one loop */
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for((void)tagno; tagno < td->tags_count; tagno++, ctx->step++) {
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/*
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* Fetch and process T from TLV.
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*/
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tag_len = ber_fetch_tag(ptr, size, &tlv_tag);
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ASN_DEBUG("Fetching tag from {%p,%ld} %02X..%02X: "
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"len %ld, tag %s",
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ptr, (long)size,
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size?*(uint8_t *)ptr:0,
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(tag_len<size&&tag_len>0)
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?*((uint8_t *)ptr + tag_len):0,
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(long)tag_len,
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ber_tlv_tag_string(tlv_tag));
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switch(tag_len) {
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case -1: RETURN(RC_FAIL);
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case 0: RETURN(RC_WMORE);
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}
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tlv_constr = BER_TLV_CONSTRUCTED(ptr);
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/*
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* If {I}, don't check anything.
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* If {I,B,C}, check B and C unless we're at I.
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*/
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if(tag_mode != 0 && ctx->step == 0) {
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/*
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* We don't expect tag to match here.
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* It's just because we don't know how the tag
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* is supposed to look like.
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*/
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} else {
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assert(tagno >= 0); /* Guaranteed by the code above */
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if(tlv_tag != td->tags[tagno]) {
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/*
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* Unexpected tag. Too bad.
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*/
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ASN_DEBUG("Expected: %s, expectation failed",
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ber_tlv_tag_string(td->tags[tagno]));
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RETURN(RC_FAIL);
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}
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}
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/*
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* Attention: if there are more tags expected,
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* ensure that the current tag is presented
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* in constructed form (it contains other tags!).
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* If this one is the last one, check that the tag form
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* matches the one given in descriptor.
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*/
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if(tagno < (td->tags_count - 1)) {
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if(tlv_constr == 0) {
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RETURN(RC_FAIL);
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}
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} else {
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if(td->last_tag_form != tlv_constr
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&& td->last_tag_form != -1) {
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RETURN(RC_FAIL);
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}
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}
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/*
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* Fetch and process L from TLV.
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*/
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len_len = ber_fetch_length(tlv_constr,
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ptr + tag_len, size - tag_len, &tlv_len);
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switch(len_len) {
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case -1: RETURN(RC_FAIL);
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case 0: RETURN(RC_WMORE);
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}
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/*
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* FIXME
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* As of today, the chain of tags
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* must either contain several indefinite length TLVs,
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* or several definite length ones.
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* No mixing is allowed.
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*/
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if(tlv_len == -1) {
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/*
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* Indefinite length.
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*/
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if(limit_len == -1) {
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expect_00_terminators++;
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} else {
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ASN_DEBUG("Unexpected indefinite length "
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"in a chain of definite lengths");
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RETURN(RC_FAIL);
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}
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ADVANCE(tag_len + len_len);
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continue;
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} else {
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if(expect_00_terminators) {
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ASN_DEBUG("Unexpected definite length "
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"in a chain of indefinite lengths");
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RETURN(RC_FAIL);
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}
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}
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/*
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* Check that multiple TLVs specify ever decreasing length,
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* which is consistent.
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*/
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if(limit_len == -1) {
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limit_len = tlv_len + tag_len + len_len;
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} else if(limit_len != tlv_len + tag_len + len_len) {
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/*
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* Inner TLV specifies length which is inconsistent
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* with the outer TLV's length value.
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*/
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ASN_DEBUG("Outer TLV is %d and inner is %d",
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limit_len, tlv_len);
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RETURN(RC_FAIL);
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}
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ADVANCE(tag_len + len_len);
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limit_len -= (tag_len + len_len);
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if((ssize_t)size > limit_len) {
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/*
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* Make sure that we won't consume more bytes
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* from the large buffer than the inferred limit.
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*/
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size = limit_len;
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}
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}
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if(opt_tlv_form)
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*opt_tlv_form = tlv_constr;
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if(expect_00_terminators)
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*last_length = -expect_00_terminators;
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else
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*last_length = tlv_len;
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RETURN(RC_OK);
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}
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