The stack maintains pointers mbedtls_ssl_context::in_xxx pointing to
various parts of the [D]TLS record header. Originally, these fields
were determined and set in ssl_parse_record_header(). By now,
ssl_parse_record_header() has been modularized to setup an instance
of the internal SSL record structure mbedtls_record, and to derive
the old in_xxx fields from that.
This commit takes a further step towards removing the in_xxx fields
by deriving them from the established record structure _outside_ of
ssl_parse_record_header() after the latter has succeeded.
One exception is the handling of possible client reconnects,
which happens in the case then ssl_parse_record_header() returns
MBEDTLS_ERR_SSL_UNEXPECTED_RECORD; since ssl_check_client_reconnect()
so far uses the in_xxx fields, they need to be derived from the
record structure beforehand.
This commit makes a first step towards modularizing the incoming record
processing by having it operate on instances of the structure mbedtls_record
representing SSL records.
So far, only record encryption/decryption operate in terms of record
instances, but the rest of the parsing doesn't. In particular,
ssl_parse_record_header() operates directly on the fixed input buffer,
setting the various ssl->in_xxx pointers and fields, and only directly
before/after calling ssl_decrypt_buf() these fields a converted to/from
mbedtls_record instances.
This commit does not yet remove the ssl->in_xxx fields, but makes a step
towards extending the lifetime of mbedtls_record structure representing
incoming records, by modifying ssl_parse_record_header() to setup an
instance of mbedtls_record, and setting the ssl->in_xxx fields from that
instance. The instance so-constructed isn't used further so far, and in
particular it is not yet consolidated with the instance set up for use
in ssl_decrypt_record(). That's for a later commit.
Previously, ssl_parse_record_header() did not check whether the current
datagram is large enough to hold a record of the advertised size. This
could lead to records being silently skipped over or backed up on the
basis of an invalid record length. Concretely, the following would happen:
1) In the case of a record from an old epoch, the record would be
'skipped over' by setting next_record_offset according to the advertised
but non-validated length, and only in the subsequent mbedtls_ssl_fetch_input()
it would be noticed in an assertion failure if the record length is too
large for the current incoming datagram.
While not critical, this is fragile, and also contrary to the intend
that MBEDTLS_ERR_SSL_INTERNAL_ERROR should never be trigger-able by
external input.
2) In the case of a future record being buffered, it might be that we
backup a record before we have validated its length, hence copying
parts of the input buffer that don't belong to the current record.
This is a bug, and it's by luck that it doesn't seem to have critical
consequences.
This commit fixes this by modifying ssl_parse_record_header() to check that
the current incoming datagram is large enough to hold a record of the
advertised length, returning MBEDTLS_ERR_SSL_INVALID_RECORD otherwise.
We don't send alerts on other instances of ill-formed records,
so why should we do it here? If we want to keep it, the alerts
should rather be sent ssl_get_next_record().
As explained in the previous commit, if mbedtls_ssl_fetch_input()
is called multiple times, all but the first call are equivalent to
bounds checks in the incoming datagram.
In DTLS, if mbedtls_ssl_fetch_input() is called multiple times without
resetting the input buffer in between, the non-initial calls are functionally
equivalent to mere bounds checks ensuring that the incoming datagram is
large enough to hold the requested data. In the interest of code-size
and modularity (removing a call to a non-const function which is logically
const in this instance), this commit replaces such a call to
mbedtls_ssl_fetch_input() by an explicit bounds check in
ssl_parse_record_header().
Previously, `ssl_handle_possible_reconnect()` was part of
`ssl_parse_record_header()`, which was required to return a non-zero error
code to indicate a record which should not be further processed because it
was invalid, unexpected, duplicate, .... In this case, some error codes
would lead to some actions to be taken, e.g. `MBEDTLS_ERR_SSL_EARLY_MESSAGE`
to potential buffering of the record, but eventually, the record would be
dropped regardless of the precise value of the error code. The error code
`MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED` returned from
`ssl_handle_possible_reconnect()` did not receive any special treatment and
lead to silent dopping of the record - in particular, it was never returned
to the user.
In the new logic this commit introduces, `ssl_handle_possible_reconnect()` is
part of `ssl_check_client_reconnect()` which is triggered _after_
`ssl_parse_record_header()` found an unexpected record, which is already in
the code-path eventually dropping the record; we want to leave this code-path
only if a valid cookie has been found and we want to reset, but do nothing
otherwise. That's why `ssl_handle_possible_reconnect()` now returns `0` unless
a valid cookie has been found or a fatal error occurred.
Availability of sufficient incoming data should be checked when
it is needed, which is in mbedtls_ssl_fetch_input(), and this
function has the necessary bounds checks in place.
The check is in terms of the internal input buffer length and is
hence likely to be originally intended to protect against overflow
of the input buffer when fetching data from the underlying
transport in mbedtls_ssl_fetch_input(). For locality of reasoning,
it's better to perform such a check close to where it's needed,
and in fact, mbedtls_ssl_fetch_input() _does_ contain an equivalent
bounds check, too, rendering the bounds check in question redundant.
mbedtls_ssl_decrypt_buf() asserts that the passed transform is not NULL,
but the function is only invoked in a single place, and this invocation
is clearly visible to be within a branch ensuring that the incoming
transform isn't NULL. Remove the assertion for the benefit of code-size.
The previous code performed architectural maximum record length checks
both before and after record decryption. Since MBEDTLS_SSL_IN_CONTENT_LEN
bounds the maximum length of the record plaintext, it suffices to check
only once after (potential) decryption.
This must not be confused with the internal check that the record
length is small enough to make the record fit into the internal input
buffer; this is done in mbedtls_ssl_fetch_input().
* origin/pr/2706:
Update Mbed Crypto to contain mbed-crypto#152
CMake: Add a subdirectory build regression test
README: Enable builds as a CMake subproject
ChangeLog: Enable builds as a CMake subproject
Remove use of CMAKE_SOURCE_DIR
* origin/pr/2632:
Adapt ChangeLog
Avoid use of large stack buffers in mbedtls_x509_write_crt_pem()
Improve documentation of mbedtls_pem_write_buffer()
Perform CRT writing in-place on the output buffer
Adapt x509write_crt.c to coding style
Remove use of CMAKE_SOURCE_DIR in case mbedtls is built from within
another CMake project. Define MBEDTLS_DIR to ${CMAKE_CURRENT_SOURCE_DIR}
in the main CMakeLists.txt file and refer to that when defining target
include paths to enable mbedtls to be built as a sub project.
Fixes#2609
Signed-off-by: Ashley Duncan <ashes.man@gmail.com>
Signed-off-by: Jaeden Amero <jaeden.amero@arm.com>
* origin/pr/2711:
programs: Make `make clean` clean all programs always
ssl_tls: Enable Suite B with subset of ECP curves
windows: Fix Release x64 configuration
platform: Include stdarg.h where needed
timing: Remove redundant include file
net_sockets: Fix typo in net_would_block()
* origin/pr/2697:
Update crypto submodule
Add all.sh component that exercises invalid_param checks
Remove mbedtls_param_failed from programs
Make it easier to define MBEDTLS_PARAM_FAILED as assert
Make test suites compatible with #include <assert.h>
Pass -m32 to the linker as well
Don't systematically rebuild programs
* origin/pr/2260:
Update crypto submodule
Remove heading spaces in tests/data_files/Makefile
Re-generate library/certs.c from script
Add new line at the end of test-ca2.key.enc
Use strict syntax to annotate origin of test data in certs.c
Add run to all.sh exercising !MBEDTLS_PEM_PARSE_C + !MBEDTLS_FS_IO
Allow DHM self test to run without MBEDTLS_PEM_PARSE_C
ssl-opt.sh: Auto-skip tests that use files if MBEDTLS_FS_IO unset
Document origin of hardcoded certificates in library/certs.c
Adapt ChangeLog
Rename server1.der to server1.crt.der
Add DER encoded files to git tree
Add build instructions to generate DER versions of CRTs and keys
Document "none" value for ca_path/ca_file in ssl_client2/ssl_server2
ssl_server2: Skip CA setup if `ca_path` or `ca_file` argument "none"
ssl_client2: Skip CA setup if `ca_path` or `ca_file` argument "none"
Correct white spaces in ssl_server2 and ssl_client2
Adapt ssl_client2 to parse DER encoded test CRTs if PEM is disabled
Adapt ssl_server2 to parse DER encoded test CRTs if PEM is disabled
Introduce a new configuration option MBEDTLS_CHECK_PARAMS_ASSERT,
which is disabled by default. When this option is enabled,
MBEDTLS_PARAM_FAILED defaults to assert rather than to a call to
mbedtls_param_failed, and <assert.h> is included.
This fixes#2671 (no easy way to make MBEDTLS_PARAM_FAILED assert)
without breaking backward compatibility. With this change,
`config.pl full` runs tests with MBEDTLS_PARAM_FAILED set to assert,
so the tests will fail if a validation check fails, and programs don't
need to provide their own definition of mbedtls_param_failed().
When MBEDTLS_SSL_ENCRYPT_THEN_MAC is enabled, but not
MBEDTLS_SSL_SOME_MODES_USE_MAC, mbedtls_ssl_derive_keys() and
build_transforms() will attempt to use a non-existent `encrypt_then_mac`
field in the ssl_transform.
Compile [ 93.7%]: ssl_tls.c
[Error] ssl_tls.c@865,14: 'mbedtls_ssl_transform {aka struct mbedtls_ssl_transform}' ha
s no member named 'encrypt_then_mac'
[ERROR] ./mbed-os/features/mbedtls/src/ssl_tls.c: In function 'mbedtls_ssl_derive_keys'
:
./mbed-os/features/mbedtls/src/ssl_tls.c:865:14: error: 'mbedtls_ssl_transform {aka str
uct mbedtls_ssl_transform}' has no member named 'encrypt_then_mac'
transform->encrypt_then_mac = session->encrypt_then_mac;
^~
Change mbedtls_ssl_derive_keys() and build_transforms() to only access
`encrypt_then_mac` if `encrypt_then_mac` is actually present.
Add a regression test to detect when we have regressions with
configurations that do not include any MAC ciphersuites.
Fixes d56ed2491b ("Reduce size of `ssl_transform` if no MAC ciphersuite is enabled")
- Explain the use of explicit ASN.1 tagging for the extensions structuree
- Remove misleading comment which suggests that mbedtls_x509_get_ext()
also parsed the header of the first extension, which is not the case.
Some functions within the X.509 module return an ASN.1 low level
error code where instead this error code should be wrapped by a
high-level X.509 error code as in the bulk of the module.
Specifically, the following functions are affected:
- mbedtls_x509_get_ext()
- x509_get_version()
- x509_get_uid()
This commit modifies these functions to always return an
X.509 high level error code.
Care has to be taken when adapting `mbetls_x509_get_ext()`:
Currently, the callers `mbedtls_x509_crt_ext()` treat the
return code `MBEDTLS_ERR_ASN1_UNEXPECTED_TAG` specially to
gracefully detect and continue if the extension structure is not
present. Wrapping the ASN.1 error with
`MBEDTLS_ERR_X509_INVALID_EXTENSIONS` and adapting the check
accordingly would mean that an unexpected tag somewhere
down the extension parsing would be ignored by the caller.
The way out of this is the following: Luckily, the extension
structure is always the last field in the surrounding structure,
so if there is some data remaining, it must be an Extension
structure, so we don't need to deal with a tag mismatch gracefully
in the first place.
We may therefore wrap the return code from the initial call to
`mbedtls_asn1_get_tag()` in `mbedtls_x509_get_ext()` by
`MBEDTLS_ERR_X509_INVALID_EXTENSIONS` and simply remove
the special treatment of `MBEDTLS_ERR_ASN1_UNEXPECTED_TAG`
in the callers `x509_crl_get_ext()` and `x509_crt_get_ext()`.
This renders `mbedtls_x509_get_ext()` unsuitable if it ever
happened that an Extension structure is optional and does not
occur at the end of its surrounding structure, but for CRTs
and CRLs, it's fine.
The following tests need to be adapted:
- "TBSCertificate v3, issuerID wrong tag"
The issuerID is optional, so if we look for its presence
but find a different tag, we silently continue and try
parsing the subjectID, and then the extensions. The tag '00'
used in this test doesn't match either of these, and the
previous code would hence return LENGTH_MISMATCH after
unsucessfully trying issuerID, subjectID and Extensions.
With the new code, any data remaining after issuerID and
subjectID _must_ be Extension data, so we fail with
UNEXPECTED_TAG when trying to parse the Extension data.
- "TBSCertificate v3, UIDs, invalid length"
The test hardcodes the expectation of
MBEDTLS_ERR_ASN1_INVALID_LENGTH, which needs to be
wrapped in MBEDTLS_ERR_X509_INVALID_FORMAT now.
Fixes#2431.
When parsing a substructure of an ASN.1 structure, no field within
the substructure must exceed the bounds of the substructure.
Concretely, the `end` pointer passed to the ASN.1 parsing routines
must be updated to point to the end of the substructure while parsing
the latter.
This was previously not the case for the routines
- x509_get_attr_type_and_value(),
- mbedtls_x509_get_crt_ext(),
- mbedtls_x509_get_crl_ext().
These functions kept using the end of the parent structure as the
`end` pointer and would hence allow substructure fields to cross
the substructure boundary. This could lead to successful parsing
of ill-formed X.509 CRTs.
This commit fixes this.
Care has to be taken when adapting `mbedtls_x509_get_crt_ext()`
and `mbedtls_x509_get_crl_ext()`, as the underlying function
`mbedtls_x509_get_ext()` returns `0` if no extensions are present
but doesn't set the variable which holds the bounds of the Extensions
structure in case the latter is present. This commit addresses
this by returning early from `mbedtls_x509_get_crt_ext()` and
`mbedtls_x509_get_crl_ext()` if parsing has reached the end of
the input buffer.
The following X.509 parsing tests need to be adapted:
- "TBSCertificate, issuer two inner set datas"
This test exercises the X.509 CRT parser with a Subject name
which has two empty `AttributeTypeAndValue` structures.
This is supposed to fail with `MBEDTLS_ERR_ASN1_OUT_OF_DATA`
because the parser should attempt to parse the first structure
and fail because of a lack of data. Previously, it failed to
obey the (0-length) bounds of the first AttributeTypeAndValue
structure and would try to interpret the beginning of the second
AttributeTypeAndValue structure as the first field of the first
AttributeTypeAndValue structure, returning an UNEXPECTED_TAG error.
- "TBSCertificate, issuer, no full following string"
This test exercises the parser's behaviour on an AttributeTypeAndValue
structure which contains more data than expected; it should therefore
fail with MBEDTLS_ERR_ASN1_LENGTH_MISMATCH. Because of the missing bounds
check, it previously failed with UNEXPECTED_TAG because it interpreted
the remaining byte in the first AttributeTypeAndValue structure as the
first byte in the second AttributeTypeAndValue structure.
- "SubjectAltName repeated"
This test should exercise two SubjectAltNames extensions in succession,
but a wrong length values makes the second SubjectAltNames extension appear
outside of the Extensions structure. With the new bounds in place, this
therefore fails with a LENGTH_MISMATCH error. This commit adapts the test
data to put the 2nd SubjectAltNames extension inside the Extensions
structure, too.
