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Improve comments across record size limit changes

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Signed-off-by: Waleed Elmelegy <waleed.elmelegy@arm.com>
This commit is contained in:
Waleed Elmelegy 2024-01-09 14:18:34 +00:00
parent 9457e67afd
commit f501790ff2
3 changed files with 22 additions and 17 deletions
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1
library/ssl_misc.h
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@ -2704,6 +2704,7 @@ int mbedtls_ssl_parse_server_name_ext(mbedtls_ssl_context *ssl,
#if defined(MBEDTLS_SSL_RECORD_SIZE_LIMIT)
#define MBEDTLS_SSL_RECORD_SIZE_LIMIT_EXTENSION_DATA_LENGTH (2)
/* This value is defined by RFC 8449 */
#define MBEDTLS_SSL_RECORD_SIZE_LIMIT_MIN (64)
MBEDTLS_CHECK_RETURN_CRITICAL

18
library/ssl_tls.c
View file

@ -3521,15 +3521,15 @@ int mbedtls_ssl_get_max_out_record_payload(const mbedtls_ssl_context *ssl)
if (ssl->transform_out != NULL &&
ssl->transform_out->tls_version == MBEDTLS_SSL_VERSION_TLS1_3) {
/* RFC 8449, section 4:
*
* This value [record_size_limit] is the length of the plaintext
* of a protected record.
* The value includes the content type and padding added in TLS 1.3
* (that is, the complete length of TLSInnerPlaintext).
*
* Thus, round down to a multiple of MBEDTLS_SSL_CID_TLS1_3_PADDING_GRANULARITY
* and subtract 1 (for the content type that will be added later)
/*
* In TLS 1.3 case, when records are protected, `max_len` as computed
* above is the maximum length of the TLSInnerPlaintext structure that
* along the plaintext payload contains the inner content type (one byte)
* and some zero padding. Given the algorithm used for padding
* in mbedtls_ssl_encrypt_buf(), compute the maximum length for
* the plaintext payload. Round down to a multiple of
* MBEDTLS_SSL_CID_TLS1_3_PADDING_GRANULARITY and
* subtract 1.
*/
max_len = ((max_len / MBEDTLS_SSL_CID_TLS1_3_PADDING_GRANULARITY) *
MBEDTLS_SSL_CID_TLS1_3_PADDING_GRANULARITY) - 1;

20
tests/ssl-opt.sh
View file

@ -4862,16 +4862,18 @@ run_test "Record Size Limit: TLS 1.3: Client-side parsing and debug output" \
-c "EncryptedExtensions: record_size_limit(28) extension received." \
-c "RecordSizeLimit: 16385 Bytes" \
# In the following (9) tests, --recordsize is the value used by the G_NEXT_CLI (3.7.2) to configure the
# maximum record size using "https://gnutls.org/reference/gnutls-gnutls.html#gnutls-record-set-max-size".
# There is currently a lower limit of 512, caused by this function not respecting the
# "%ALLOW_SMALL_RECORDS" priority string and not using the more recent function
# https://gnutls.org/reference/gnutls-gnutls.html#gnutls-record-set-max-recv-size.
# In the following tests, --recordsize is the value used by the G_NEXT_CLI (3.7.2) to configure the
# maximum record size using gnutls_record_set_max_size()
# (https://gnutls.org/reference/gnutls-gnutls.html#gnutls-record-set-max-size).
# There is currently a lower limit of 512, caused by gnutls_record_set_max_size()
# not respecting the "%ALLOW_SMALL_RECORDS" priority string and not using the
# more recent function gnutls_record_set_max_recv_size()
# (https://gnutls.org/reference/gnutls-gnutls.html#gnutls-record-set-max-recv-size).
# There is currently an upper limit of 4096, caused by the cli arg parser:
# https://gitlab.com/gnutls/gnutls/-/blob/3.7.2/src/cli-args.def#L395.
# Thus, these tests are currently limit to that value range.
# Moreover, the value sent in the extension is expected to be larger by one compared
# to the value passed on the cli:
# Thus, these tests are currently limited to the value range 512-4096.
# Also, the value sent in the extension will be one larger than the value
# set at the command line:
# https://gitlab.com/gnutls/gnutls/-/blob/3.7.2/lib/ext/record_size_limit.c#L142
# Currently test certificates being used do not fit in 513 record size limit
@ -5050,6 +5052,8 @@ run_test "Record Size Limit: TLS 1.3 m->m: both peer comply with record size
-s "Maximum outgoing record payload length is 16383" \
-s "Maximum incoming record payload length is 16384"
# End of Record size limit tests
# Tests for renegotiation
# Renegotiation SCSV always added, regardless of SSL_RENEGOTIATION