513 lines
17 KiB
C
513 lines
17 KiB
C
/*
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* Message Processing Stack, Reader implementation
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*
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* Copyright The Mbed TLS Contributors
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* This file is part of Mbed TLS (https://tls.mbed.org)
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*/
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#include "mps_reader.h"
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#include "mps_common.h"
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#include "mps_trace.h"
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#include <string.h>
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#if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
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!defined(inline) && !defined(__cplusplus)
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#define inline __inline
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#endif
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#if defined(MBEDTLS_MPS_TRACE)
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static int trace_id = TRACE_BIT_READER;
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#endif /* MBEDTLS_MPS_TRACE */
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/*
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* GENERAL NOTE ON CODING STYLE
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*
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* The following code intentionally separates memory loads
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* and stores from other operations (arithmetic or branches).
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* This leads to the introduction of many local variables
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* and significantly increases the C-code line count, but
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* should not increase the size of generated assembly.
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*
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* This reason for this is twofold:
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* (1) It will ease verification efforts using the VST
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* whose program logic cannot directly reason
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* about instructions containing a load or store in
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* addition to other operations (e.g. *p = *q or
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* tmp = *p + 42).
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* (2) Operating on local variables and writing the results
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* back to the target contexts on success only
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* allows to maintain structure invariants even
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* on failure - this in turn has two benefits:
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* (2.a) If for some reason an error code is not caught
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* and operation continues, functions are nonetheless
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* called with sane contexts, reducing the risk
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* of dangerous behavior.
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* (2.b) Randomized testing is easier if structures
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* remain intact even in the face of failing
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* and/or non-sensical calls.
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* Moreover, it might even reduce code-size because
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* the compiler need not write back temporary results
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* to memory in case of failure.
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*
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*/
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static inline void mps_reader_zero( mbedtls_reader *rd )
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{
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/* A plain memset() would likely be more efficient,
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* but the current way of zeroing makes it harder
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* to overlook fields which should not be zero-initialized.
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* It's also more suitable for VF efforts since it
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* doesn't require reasoning about structs being
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* interpreted as unstructured binary blobs. */
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static mbedtls_reader const zero =
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{ .frag = NULL,
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.frag_len = 0,
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.commit = 0,
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.end = 0,
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.pending = 0,
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.acc = NULL,
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.acc_len = 0,
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.acc_avail = 0,
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.acc_share = { .acc_remaining = 0 }
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};
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*rd = zero;
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}
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int mbedtls_reader_init( mbedtls_reader *rd,
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unsigned char *acc,
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mbedtls_mps_size_t acc_len )
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{
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TRACE_INIT( "reader_init, acc len %u", (unsigned) acc_len );
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mps_reader_zero( rd );
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rd->acc = acc;
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rd->acc_len = acc_len;
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RETURN( 0 );
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}
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int mbedtls_reader_free( mbedtls_reader *rd )
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{
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TRACE_INIT( "reader_free" );
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mps_reader_zero( rd );
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RETURN( 0 );
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}
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int mbedtls_reader_feed( mbedtls_reader *rd,
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unsigned char *new_frag,
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mbedtls_mps_size_t new_frag_len )
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{
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unsigned char *acc;
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mbedtls_mps_size_t copy_to_acc;
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TRACE_INIT( "reader_feed, frag %p, len %u",
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(void*) new_frag, (unsigned) new_frag_len );
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if( new_frag == NULL )
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RETURN( MBEDTLS_ERR_MPS_READER_INVALID_ARG );
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MBEDTLS_MPS_STATE_VALIDATE_RAW( rd->frag == NULL,
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"mbedtls_reader_feed() requires reader to be in producing mode" );
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acc = rd->acc;
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if( acc != NULL )
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{
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mbedtls_mps_size_t aa, ar;
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ar = rd->acc_share.acc_remaining;
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aa = rd->acc_avail;
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copy_to_acc = ar;
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if( copy_to_acc > new_frag_len )
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copy_to_acc = new_frag_len;
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acc += aa;
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if( copy_to_acc > 0 )
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memcpy( acc, new_frag, copy_to_acc );
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TRACE( trace_comment, "Copy new data of size %u of %u into accumulator at offset %u",
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(unsigned) copy_to_acc, (unsigned) new_frag_len, (unsigned) aa );
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/* Check if, with the new fragment, we have enough data. */
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ar -= copy_to_acc;
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if( ar > 0 )
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{
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/* Need more data */
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aa += copy_to_acc;
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rd->acc_share.acc_remaining = ar;
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rd->acc_avail = aa;
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RETURN( MBEDTLS_ERR_MPS_READER_NEED_MORE );
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}
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TRACE( trace_comment, "Enough data available to serve user request" );
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rd->acc_share.frag_offset = aa;
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aa += copy_to_acc;
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rd->acc_avail = aa;
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}
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else
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{
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rd->acc_share.frag_offset = 0;
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}
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rd->frag = new_frag;
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rd->frag_len = new_frag_len;
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rd->commit = 0;
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rd->end = 0;
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RETURN( 0 );
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}
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int mbedtls_reader_get( mbedtls_reader *rd,
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mbedtls_mps_size_t desired,
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unsigned char **buffer,
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mbedtls_mps_size_t *buflen )
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{
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unsigned char *frag, *acc;
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mbedtls_mps_size_t end, fo, fl, frag_fetched, frag_remaining;
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TRACE_INIT( "reader_get %p, desired %u", (void*) rd, (unsigned) desired );
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frag = rd->frag;
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MBEDTLS_MPS_STATE_VALIDATE_RAW( frag != NULL,
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"mbedtls_reader_get() requires reader to be in consuming mode" );
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/* The fragment offset indicates the offset of the fragment
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* from the accmulator, if the latter is present. Use a offset
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* of \c 0 if no accumulator is used. */
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acc = rd->acc;
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if( acc == NULL )
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fo = 0;
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else
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fo = rd->acc_share.frag_offset;
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TRACE( trace_comment, "frag_off %u, end %u, acc_avail %d",
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(unsigned) fo, (unsigned) rd->end,
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acc == NULL ? -1 : (int) rd->acc_avail );
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/* Check if we're still serving from the accumulator. */
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end = rd->end;
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if( end < fo )
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{
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TRACE( trace_comment, "Serve the request from the accumulator" );
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if( fo - end < desired )
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{
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/* Illustration of supported and unsupported cases:
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*
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* - Allowed #1
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*
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* +-----------------------------------+
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* | frag |
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* +-----------------------------------+
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*
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* end end+desired
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* | |
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* +-----v-------v-------------+
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* | acc |
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* +---------------------------+
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* | |
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* fo/frag_offset aa/acc_avail
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*
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* - Allowed #2
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*
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* +-----------------------------------+
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* | frag |
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* +-----------------------------------+
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*
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* end end+desired
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* | |
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* +----------v----------------v
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* | acc |
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* +---------------------------+
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* | |
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* fo/frag_offset aa/acc_avail
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*
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* - Not allowed #1 (could be served, but we don't actually use it):
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*
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* +-----------------------------------+
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* | frag |
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* +-----------------------------------+
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*
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* end end+desired
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* | |
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* +------v-------------v------+
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* | acc |
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* +---------------------------+
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* | |
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* fo/frag_offset aa/acc_avail
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*
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*
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* - Not allowed #2 (can't be served with a contiguous buffer):
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*
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* +-----------------------------------+
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* | frag |
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* +-----------------------------------+
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*
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* end end + desired
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* | |
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* +------v--------------------+ v
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* | acc |
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* +---------------------------+
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* | |
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* fo/frag_offset aa/acc_avail
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*
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* In case of Allowed #1 and #2 we're switching to serve from
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* `frag` starting from the next call to mbedtls_reader_get().
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*/
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mbedtls_mps_size_t aa;
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aa = rd->acc_avail;
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if( aa - end != desired )
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{
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/* It might be possible to serve some of these situations by
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* making additional space in the accumulator, removing those
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* parts that have already been committed.
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* On the other hand, this brings additional complexity and
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* enlarges the code size, while there doesn't seem to be a use
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* case where we don't attempt exactly the same `get` calls when
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* resuming on a reader than what we tried before pausing it.
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* If we believe we adhere to this restricted usage throughout
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* the library, this check is a good opportunity to
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* validate this. */
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RETURN( MBEDTLS_ERR_MPS_READER_INCONSISTENT_REQUESTS );
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}
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}
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acc += end;
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*buffer = acc;
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if( buflen != NULL )
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*buflen = desired;
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end += desired;
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rd->end = end;
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rd->pending = 0;
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RETURN( 0 );
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}
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/* Attempt to serve the request from the current fragment */
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TRACE( trace_comment, "Serve the request from the current fragment." );
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fl = rd->frag_len;
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frag_fetched = end - fo; /* The amount of data from the current fragment
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* that has already been passed to the user. */
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frag += frag_fetched;
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frag_remaining = fl - frag_fetched; /* Remaining data in fragment */
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/* Check if we can serve the read request from the fragment. */
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if( frag_remaining < desired )
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{
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TRACE( trace_comment, "There's not enough data in the current fragment to serve the request." );
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/* There's not enough data in the current fragment,
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* so either just RETURN what we have or fail. */
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if( buflen == NULL )
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{
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if( frag_remaining > 0 )
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{
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rd->pending = desired - frag_remaining;
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TRACE( trace_comment, "Remember to collect %u bytes before re-opening",
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(unsigned) rd->pending );
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}
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RETURN( MBEDTLS_ERR_MPS_READER_OUT_OF_DATA );
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}
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desired = frag_remaining;
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}
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/* There's enough data in the current fragment to serve the
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* (potentially modified) read request. */
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*buffer = frag;
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if( buflen != NULL )
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*buflen = desired;
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end += desired;
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rd->end = end;
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rd->pending = 0;
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RETURN( 0 );
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}
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int mbedtls_reader_commit( mbedtls_reader *rd )
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{
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unsigned char *acc;
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mbedtls_mps_size_t aa, end, fo, shift;
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TRACE_INIT( "reader_commit" );
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MBEDTLS_MPS_STATE_VALIDATE_RAW( rd->frag != NULL,
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"mbedtls_reader_commit() requires reader to be in consuming mode" );
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acc = rd->acc;
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end = rd->end;
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if( acc == NULL )
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{
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TRACE( trace_comment, "No accumulator, just shift end" );
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rd->commit = end;
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RETURN( 0 );
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}
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fo = rd->acc_share.frag_offset;
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if( end >= fo )
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{
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TRACE( trace_comment, "Started to serve fragment, get rid of accumulator" );
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shift = fo;
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aa = 0;
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}
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else
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{
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TRACE( trace_comment, "Still serving from accumulator" );
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aa = rd->acc_avail;
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shift = end;
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memmove( acc, acc + shift, aa - shift );
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aa -= shift;
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}
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end -= shift;
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fo -= shift;
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rd->acc_share.frag_offset = fo;
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rd->acc_avail = aa;
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rd->commit = end;
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rd->end = end;
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TRACE( trace_comment, "Final state: (end=commit,fo,avail) = (%u,%u,%u)",
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(unsigned) end, (unsigned) fo, (unsigned) aa );
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RETURN( 0 );
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}
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int mbedtls_reader_reclaim( mbedtls_reader *rd,
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mbedtls_mps_size_t *paused )
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{
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unsigned char *frag, *acc;
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mbedtls_mps_size_t pending, commit;
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mbedtls_mps_size_t al, fo, fl;
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TRACE_INIT( "reader_reclaim" );
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if( paused != NULL )
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*paused = 0;
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frag = rd->frag;
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MBEDTLS_MPS_STATE_VALIDATE_RAW( frag != NULL,
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"mbedtls_reader_reclaim() requires reader to be in consuming mode" );
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acc = rd->acc;
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pending = rd->pending;
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commit = rd->commit;
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fl = rd->frag_len;
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if( acc == NULL )
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fo = 0;
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else
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fo = rd->acc_share.frag_offset;
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if( pending == 0 )
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{
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TRACE( trace_comment, "No unsatisfied read-request has been logged." );
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/* Check if there's data left to be consumed. */
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if( commit < fo || commit - fo < fl )
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{
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TRACE( trace_comment, "There is data left to be consumed." );
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rd->end = commit;
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RETURN( MBEDTLS_ERR_MPS_READER_DATA_LEFT );
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}
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TRACE( trace_comment, "The fragment has been completely processed and committed." );
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}
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else
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{
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mbedtls_mps_size_t frag_backup_offset;
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mbedtls_mps_size_t frag_backup_len;
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TRACE( trace_comment, "There has been an unsatisfied read-request with %u bytes overhead.",
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(unsigned) pending );
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if( acc == NULL )
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{
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TRACE( trace_comment, "No accumulator present" );
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RETURN( MBEDTLS_ERR_MPS_READER_NEED_ACCUMULATOR );
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}
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al = rd->acc_len;
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/* Check if the upper layer has already fetched
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* and committed the contents of the accumulator. */
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if( commit < fo )
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{
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/* No, accumulator is still being processed. */
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int overflow;
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TRACE( trace_comment, "Still processing data from the accumulator" );
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overflow =
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( fo + fl < fo ) || ( fo + fl + pending < fo + fl );
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if( overflow || al < fo + fl + pending )
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{
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rd->end = commit;
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rd->pending = 0;
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TRACE( trace_error, "The accumulator is too small to handle the backup." );
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TRACE( trace_error, "* Remaining size: %u", (unsigned) al );
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TRACE( trace_error, "* Needed: %u (%u + %u + %u)",
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(unsigned) ( fo + fl + pending ),
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(unsigned) fo, (unsigned) fl, (unsigned) pending );
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RETURN( MBEDTLS_ERR_MPS_READER_ACCUMULATOR_TOO_SMALL );
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}
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frag_backup_offset = 0;
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frag_backup_len = fl;
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}
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else
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{
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/* Yes, the accumulator is already processed. */
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int overflow;
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TRACE( trace_comment, "The accumulator has already been processed" );
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frag_backup_offset = commit;
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frag_backup_len = fl - commit;
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overflow = ( frag_backup_len + pending < pending );
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if( overflow ||
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al - fo < frag_backup_len + pending )
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{
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rd->end = commit;
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rd->pending = 0;
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TRACE( trace_error, "The accumulator is too small to handle the backup." );
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TRACE( trace_error, "* Remaining size: %u", (unsigned) ( al - fo ) );
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TRACE( trace_error, "* Needed: %u (%u + %u)",
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(unsigned) ( frag_backup_len + pending ),
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(unsigned) frag_backup_len, (unsigned) pending );
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RETURN( MBEDTLS_ERR_MPS_READER_ACCUMULATOR_TOO_SMALL );
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}
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}
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frag += frag_backup_offset;
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acc += fo;
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memcpy( acc, frag, frag_backup_len );
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TRACE( trace_comment, "Backup %u bytes into accumulator",
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(unsigned) frag_backup_len );
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rd->acc_avail = fo + frag_backup_len;
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rd->acc_share.acc_remaining = pending;
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if( paused != NULL )
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*paused = 1;
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}
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rd->frag = NULL;
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rd->frag_len = 0;
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rd->commit = 0;
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rd->end = 0;
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rd->pending = 0;
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TRACE( trace_comment, "Final state: aa %u, al %u, ar %u",
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(unsigned) rd->acc_avail, (unsigned) rd->acc_len,
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(unsigned) rd->acc_share.acc_remaining );
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RETURN( 0 );
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}
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