The previous code writes the content (the EC curve list) of the extension
before writing the extension length field at the beginning, which is common
in the library in places where we don't know the length upfront. Here,
however, we do traverse the EC curve list upfront to infer its length
and do the bounds check, so we can reorder the code to write the extension
linearly and hence improve readability.
This commit introduces the option MBEDTLS_SSL_CONF_SINGLE_EC
which can be used to register a single supported elliptic curve
at compile time. It replaces the runtime configuration API
mbedtls_ssl_conf_curves() which allows to register a _list_
of supported elliptic curves.
In contrast to other options used to hardcode configuration options,
MBEDTLS_SSL_CONF_SINGLE_EC isn't a numeric option, but instead it's
only relevant if it's defined or not. To actually set the single
elliptic curve that should be supported, numeric options
MBEDTLS_SSL_CONF_SINGLE_EC_TLS_ID
MBEDTLS_SSL_CONF_SINGLE_EC_GRP_ID
must both be defined and provide the TLS ID and the Mbed TLS internal
ID and the chosen curve, respectively.
For both client/server the EC curve list is assumed not to be NULL:
- On the client-side, it's assumed when writing the
supported elliptic curve extension:
c54ee936d7/library/ssl_cli.c (L316)
- On the server, it is assumed when searching for a
suitable curve for the ECDHE exchange:
c54ee936d7/library/ssl_srv.c (L3200)
It is therefore not necessary to check this in mbedtls_ssl_check_curve().
ssl_write_supported_elliptic_curves_ext() is guarded by
```
#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
```
each of which implies (by check_config.h) that MBEDTLS_ECP_C
is enabled.
The fields
- mbedtls_ssl_handshake_params::max_major_ver,
- mbedtls_ssl_handshake_params::max_minor_ver
are used only for server-side RSA-based key exchanges
can be removed otherwise.
Reasons:
- If the transport type is fixed at compile-time,
mbedtls_ssl_read_version() and mbedtls_ssl_write_version()
are called with a compile-time determined `transport`
parameter, so the transport-type branch in their body
can be eliminated at compile-time.
- mbedtls_ssl_read_version() is called with addresses of
local variables, which so far need to be put on the stack
to be addressable. Inlining the call allows to read directly
into the registers holding these local variables.
This saves 60 bytes w.r.t. the measurement performed by
> ./scripts/baremetal.sh --rom --gcc
If the minor/major version is enforced at compile-time, the `major_ver`
and `minor_ver` fields in `mbedtls_ssl_context` are redundant and can
be removed.
This commit introduces the numeric compile-time constants
- MBEDTLS_SSL_CONF_MIN_MINOR_VER
- MBEDTLS_SSL_CONF_MAX_MINOR_VER
- MBEDTLS_SSL_CONF_MIN_MAJOR_VER
- MBEDTLS_SSL_CONF_MAX_MAJOR_VER
which, when defined, overwrite the runtime configurable fields
mbedtls_ssl_config::min_major_ver etc. in the SSL configuration.
As for the preceding case of the ExtendedMasterSecret configuration,
it also introduces and puts to use getter functions for these variables
which evaluate to either a field access or the macro value, maintaining
readability of the code.
The runtime configuration API mbedtls_ssl_conf_{min|max}_version()
is kept for now but has no effect if MBEDTLS_SSL_CONF_XXX are set.
This is likely to be changed in a later commit but deliberately omitted
for now, in order to be able to study code-size benefits earlier in the
process.
This commit restructures ssl_ciphersuites.h and ssl_ciphersuites.c to
define all ciphersuite helper functions static inline in ssl_ciphersuites.h
if MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE is set, and to otherwise put their
definitions in ssl_ciphersuites.c.
If MBEDTLS_SSL_SINGLE_CIPHERSUITE is enabled, the type
mbedtls_ssl_ciphersuite_handle_t
is logically a boolean (concretely realized as `unsigned char`),
containing the invalid handle and the unique valid handle, which
represents the single enabled ciphersuite.
The SSL session structure mbedtls_ssl_session contains an instance
of mbedtls_ssl_ciphersuite_handle_t which is guaranteed to be valid,
and which is hence redundant in any two-valued implementation of
mbedtls_ssl_ciphersuite_handle_t.
This commit replaces read-uses of
mbedtls_ssl_session::ciphersuite_info
by a getter functions which, and defines this getter function
either by just reading the field from the session structure
(in case MBEDTLS_SSL_SINGLE_CIPHERSUITE is disabled), or by
returning the single valid ciphersuite handle (in case
MBEDTLS_SSL_SINGLE_CIPHERSUITE is enabled) and removing the
field from mbedtls_ssl_session in this case.
If MBEDTLS_SSL_SINGLE_CIPHERSUITE is enabled, it overwrites
the runtime configuration of supported ciphersuites, which
includes both the configuration API and the fields which are
used to store the configuration. Both are therefore no longer
needed and should be removed for the benefit of code-size,
memory usage, and API clarity (no accidental hiccup of runtime
vs. compile-time configuration possible).
The configuration API mbedtls_ssl_conf_ciphersuites() has
already been removed in case MBEDTLS_SSL_SINGLE_CIPHERSUITE,
and this commit removes the field
mbedtls_ssl_config::ciphersuite_list
which it updates.
If MBEDTLS_SSL_SINGLE_CIPHERSUITE is enabled, the type
mbedtls_ssl_ciphersuite_handle_t
is logically a boolean (concretely realized as `unsigned char`),
containing the invalid handle and the unique valid handle, which
represents the single enabled ciphersuite.
The SSL handshake structure mbedtls_ssl_handshake_params contains
an instance of mbedtls_ssl_ciphersuite_handle_t which is guaranteed
to be valid, and which is hence redundant in any two-valued
implementation of mbedtls_ssl_ciphersuite_handle_t.
This commit replaces read-uses of
mbedtls_ssl_handshake_params::ciphersuite_info
by a getter functions which, and defines this getter function
either by just reading the field from the handshake structure
(in case MBEDTLS_SSL_SINGLE_CIPHERSUITE is disabled), or by
returning the single valid ciphersuite handle (in case
MBEDTLS_SSL_SINGLE_CIPHERSUITE is enabled) and removing the
field from mbedtls_ssl_handshake_params in this case.
This commit adapts the ClientHello parsing routines in ssl_srv.c
to use the ciphersuite traversal macros
MBEDTLS_SSL_BEGIN_FOR_EACH_CIPHERSUITE
MBEDTLS_SSL_END_FOR_EACH_CIPHERSUITE
introduced in the last commit, thereby making them work
both with and without MBEDTLS_SSL_SINGLE_CIPHERSUITE.
Another notable change concerns the ssl_ciphersuite_match:
Previous, this function would take a ciphersuite ID and a
pointer to a destination ciphersuite info structure as input
and write eithe NULL or a valid ciphersuite info structure
to that destination address, depending on whether the suite
corresponding to the given ID was suitable or not. The
function would always return 0 outside of a fatal error.
This commit changes this to ssl_ciphersuite_is_match() which
instead already takes a ciphersuite handle (which outside
of a hardcoded ciphersuite is the same as the ptr to a
ciphersuite info structure) and returns 0 or 1 (or a
negative error code in case of a fatal error) indicating
whether the suite corresponding to the handle was acceptable
or not. The conversion of the ciphersuite ID to the ciphersuite
info structure is done prior to calling ssl_ciphersuite_is_match().
This commit modifies the ClientHello writing routine ssl_write_client_hello
in ssl_cli.c to switch between
(a) listing all runtime configured ciphersuites
(in case MBEDTLS_SSL_SINGLE_CIPHERSUITE is not defined)
(b) listing just the single hardcoded ciphersuite
(in case MBEDTLS_SSL_SINGLE_CIPHERSUITE is defined)
The approach taken is to introduce a pair of helper macros
MBEDTLS_SSL_BEGIN_FOR_EACH_CIPHERSUITE( ssl, ver, info )
MBEDTLS_SSL_END_FOR_EACH_CIPHERSUITE
which when delimiting a block of code lead to that block of
code being run once for each ciphersuite that's enabled in the
context `ssl` and version `ver`, referenced through the (fresh)
`info` variable. Internally, this is implemented either through
a plain `for` loop traversing the runtime configured ciphersuite
list (if MBEDTLS_SSL_SINGLE_CIPHERSUITE is disabled) or by just
hardcoding `info` to the single enabled ciphersuite (if
MBEDTLS_SSL_SINGLE_CIPHERSUITE is enabled).
These helper macros will prove useful whereever previous code
traversed the runtime configured ciphersuite list, but adaptations
of those occasions outside ClientHello writing are left for later
commits.
This commit is a step towards the goal of allowing to hardcode the choice
of a single ciphersuite at compile-time. The hoped for benefit of this is
that whereever a ciphersuite attribute is queried and checked against a
compile-time constant, the check can be recognized as either true or false
at compile-time, hence leading to a code-size reduction.
For this to work, the ciphersuite attribute getter functions
mbedtls_ssl_suite_get_xxx() will be modified to return something
the compiler can recognize as a compile-time constant. In particular,
in order to avoid relying on constant propagation abilities of the
compiler, these functions should ideally return constant symbols
(instead of, say, fields in a globally const structure instance).
This puts us in the following situation: On the one hand, there's the
array of ciphersuite information structures defining the attribute of
those ciphersuites the stack knows about. On the other hand, we need
direct access to those fields through constant symbols in the getter
functions.
In order to avoid any duplication of information, this commit exemplifies
how ciphersuites can be conveniently defined on the basis of macro
definitions, and how the corresponding instances of the ciphersuite
information structure can be auto-generated from this.
In the approach, to add support for a ciphersuite with official name
NAME (such as TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8), the following macro
constants need to be defined in ssl_ciphersuites.h:
MBEDTLS_SUITE__ NAME __ID
MBEDTLS_SUITE__ NAME __NAME
MBEDTLS_SUITE__ NAME __CIPHER
MBEDTLS_SUITE__ NAME __MAC
...
To make check-names.sh happy, one also needs a dummy macro
MBEDTLS_SUITE__ NAME()
These ciphersuite attribute values can then be queried via
MBEDTLS_SSL_SUITE_ID( NAME_MACRO )
...
where NAME_MACRO can be any macro expanding to a defined NAME.
Further, a convenience macro
MBEDTLS_SSL_SUITE_INFO( NAME_MACRO )
is provided that again takes a macro NAME_MACRO expanding to a
defined NAME, and itself expands to an instance of
mbedtls_ssl_ciphersuite_info_t using the macro attributes
defined for NAME. This macro is then used in ssl_ciphersuites.c
when defining the array of known ciphersuite information structures,
(a) without duplicating the information, and (b) with increased
readability, because there's only one line for each ciphersuite.
This commit introduces an internal zero-cost abstraction layer for
SSL ciphersuites: Instead of addressing ciphersuites via pointers
to instances of mbedtls_ssl_ciphersuite_t and accessing their fields
directly, this commit introduces an opaque type
mbedtls_ssl_ciphersuite_handle_t,
and getter functions
mbedtls_ssl_suite_get_xxx()
operating on ciphersuite handles.
The role of NULL is played by a new macro constant
MBEDTLS_SSL_CIPHERSUITE_INVALID_HANDLE
which results of functions returning handles can be checked against.
(For example, when doing a lookup of a ciphersuite from a peer-provided
ciphersuite ID in the per's Hello message).
The getter functions have the validity of the handle as a precondition
and are undefined if the handle is invalid.
So far, there's only one implementation of this abstraction layer, namely
mbedtls_ssl_ciphersuite_handle_t being mbedtls_ssl_ciphersuite_t const *
and
getter functions being field accesses.
In subsequent commits, however, the abstraction layer will be useful
to save code in the situation where only a single ciphersuite is enabled.
* origin/pr/2700:
Changelog entry for HAVEGE fix
Prevent building the HAVEGE module on platforms where it doesn't work
Fix misuse of signed ints in the HAVEGE module
So far, the client-proposed list of elliptic curves was stored for the
duration of the entire handshake in a heap-allocated buffer referenced
from mbedtls_ssl_handshake_params::curves. It is used in the following
places:
1) When the server chooses a suitable ciphersuite, it checks that
it has a certificate matching the ciphersuite; in particular, if
the ciphersuite involves ECDHE, the server needs an EC certificate
with a curve suitable for the client.
2) When performing the ECDHE key exchange, the server choose one
curve among those proposed by the client which matches the server's
own supported curve configuration.
This commit removes the hold back the entire client-side curve list
during the handshake, by performing (1) and (2) on during ClientHello
parsing, and in case of (2) only remembering the curve chosen for ECDHE
within mbedtls_ssl_handshake_params.
Fix an "unused variable" warning that happened in some configurations
(without EC, found by depend-pkalg.pl) and was not present in any parent PR
but only in the result of merging them: one of the PRs clarified the
distinction between `ret` and `verify_ret` and the other removed one
occurrence of using `ret`, and the conjunction of the two made `ret` unused in
some cases. Resolving by reducing the scope of that variable.
* restricted/pr/608:
programs: Make `make clean` clean all programs always
ssl_tls: Enable Suite B with subset of ECP curves
windows: Fix Release x64 configuration
timing: Remove redundant include file
net_sockets: Fix typo in net_would_block()
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
Update library to 2.16.2
Use 'config.pl baremetal' in all.sh
Clarify ChangeLog entry for fix to #1628Fix#2370, minor typos and spelling mistakes
Add Changelog entry for clang test-ref-configs.pl fix
Enable more compiler warnings in tests/Makefile
Change file scoping of test helpers.function
* restricted/pr/594:
Adapt baremetal.h and baremetal.sh
Don't incl. CAs in CertReq message in baremetal build
Allow config'n of incl of CertificateReq CA list Y/N at compile-time
Allow configuration of endpoint (cli/srv) at compile-time
Allow configuration of read timeouts at compile-time
Allow configuration of ConnectionID at compile-time
Allow compile-time configuration of legacy renegotiation
Allow compile-time configuration of authentication mode
Allow compile-time configuration of DTLS badmac limit
Allow compile-time configuration of DTLS anti replay
* restricted/pr/601: (27 commits)
Fix compile-time guard for optional field in struct
Move code to reduce probability of conflicts
Fix typos caught by check-names.sh
Clarify conditions related to resumption in client
Introduce getter function for renego_status
Add getter function for handshake->resume
Remove now-redundant code
Remove cache callbacks from config on client
Fix a few style issues
Expand documentation of new options a bit
Fix renaming oversight in documentation
Remove backticks in doxygen in config.h
Declare dependency on tickets for two ssl-opt.sh tests
Exclude new negative options from config.pl full
Restore config.h defaults
Address review comments
Fix ssl_cli resumption guards
Fix check-files, check-names and check-generated-features
Add test to all.sh
Add changelog entry
...
* restricted/pr/584: (140 commits)
Remove superfluous new line in x509.c
Add comment about X.509 name comparison of buffer with itself
[Fixup] Add missing PK release call in Cert Verify parsing
Fix guard controlling whether nested acquire calls are allowed
Add X.509 CRT test for nested calls for CRT frame / PK acquire
Don't return threading error on release()-without-acquire() calls
Don't allow nested CRT acquire()-calls if MBEDTLS_X509_ALWAYS_FLUSH
Make X.509 CRT cache reference counting unconditional
Remove memory buffer alloc from i386 test in all.sh
Don't mention pk_sign() in the context of public-key contexts
Don't use assertion for failures of mbedtls_x509_crt_x_acquire()
Fix copy pasta in x509_crt.h
Reference copy-less versions of X.509 CRT frame/PK getters
x509_crt.c: Add blank line to increase readability
[FIXUP] Fix bug in ASN.1 traversal of silently ignored tag
[FIXUP] Fix typo in declaration of mbedtls_x509_memcasecmp()
Move signature-info extraction out of MBEDTLS_X509_REMOVE_INFO
Fix certificate validity checking logic to work with !TIME_DATE
Simplify X.509 CRT version check in UID parsing
Remove unused variable warning in on-demand X.509 parsing
...
Introduces MBEDTLS_SSL_CONF_CERT_REQ_CA_LIST which allows to configure
at compile-time whether a CA list should be included in the
CertificateRequest message sent by the server.
Impact on code-size:
| | GCC 8.2.1 | ARMC5 5.06 | ARMC6 6.12 |
| --- | --- | --- | --- |
| `libmbedtls.a` before | 23131 | 23805 | 26673 |
| `libmbedtls.a` after | 23099 | 23781 | 26639 |
| gain in Bytes | 32 | 24 | 34 |
Introduces MBEDTLS_SSL_CONF_BADMAC_LIMIT to fix the maximum
number of records with bad MAC tolerated in DTLS at compile-time.
Impact on code-size:
| | GCC | ARMC5 | ARMC6 |
| --- | --- | --- | --- |
| `libmbedtls.a` before | 23511 | 24049 | 27903 |
| `libmbedtls.a` after | 23487 | 24025 | 27885 |
| gain in Bytes | 24 | 24 | 18 |
mbedtls_ssl_read() can fail non-fatally, in which case
ssl_parse_certificate_verify() returned immediately without
calling mbedtls_x509_crt_pk_release(), which in turn lead
to a fatal error because of nested acquire calls in the
next call to the function.
While not strictly related to this PR, this change improves readability in
some resumption-related runtime conditions that previously had rather ugly
preprocessor directives in the middle of already complex predicates.
Due to previous change of conditions, this is now in the 'else' branch of 'if
resume == 1' and the only allowed values are 0 or 1, so setting to 0 is
redundant.
Add a new configuration option MBEDTLS_SSL_SESSION_RESUMPTION
to enable/disable the session resumption feature including
ticket and cache based session resumption.
Resource counting as a safe-guard against nested acquire calls
is implemented if and only if MBEDTLS_X509_ALWAYS_FLUSH is disabled
_or_ MBEDTLS_THREADING_C is enabled.
Forbidding nested calls to acquire() allows to remove the reference
counting logic and hence saving some bytes of code. This is valuable
because MBEDTLS_X509_ALWAYS_FLUSH is likely to be used on constrained
systems where code-size is limited.
Previously, reference counting for the CRT frames and PK contexts
handed out by mbedtls_x509_crt_{frame|pk}_acquire() was implemented
only in case threading support was enabled, which leaves the door
open for a potential use-after-free should a single-threaded application
use nested calls to mbedtls_x509_crt_acquire().
Since Mbed TLS itself does not use such nested calls, it might be
preferred long-term to forbid nesting of acquire calls on the API
level, and hence get rid of reference counting in the interest of
code-size benefits. However, this can be considered as an optimization
of X.509 on demand parsing, and for now this commit introduces
reference counting unconditionally to have a safe version of
on demand parsing to build further optimizations upon.
During rebase, the definition of ::mbedtls_x509_crt_sig_info
as well as x509_crt_free_sig_info() and x509_crt_get_sig_info()
were accidentally guarded by !MBEDTLS_X509_REMOVE_INFO.
This commit moves their definition outside of that guard.
If MBEDTLS_HAVE_TIME_DATE is undefined, the functions
`mbedtls_x509_time_is_past()` and `mbedtls_x509_time_is_future()`
are still defined but return `0` (that is, no time is seen to in
the past or future). To maintain functional correctness, this
means that these functions have to be called in a way where
the condition being checked for is the erroneous one: Concretely,
one shouldn't check that a CRT's `validFrom` is in the past,
or that its `validTo` is in the future, because that would
fail if !MBEDTLS_HAVE_TIME_DATE. Instead, one should check
that `validFrom` is NOT in the future, and `validTo` is NOT
in the past. That was the logic previously, but an uncautious
change during transition to X.509 on-demand parsing has
changed it. This commit fixes this.
WHen parsing the CRT version, we already check that
version is either 1, 2, or 3, so checking whether
version == 2 or version == 3 is equivalent to
version != 1.
Previously, only one thread could access the parsing cache of an X.509 CRT
at a time. Firstly, this leads to significant performance penalties on
systems running many concurrent threads which share CRT structures --
for example, server threads sharing an SSL configuration containing the
server CRT. Secondly, the locking should be logically unnecessary, because
the threads are supposed to access the CRT frame and PK in a read-only,
or at least thread-safe manner.
This commit modifies the X.509 CRT cache implementation by allowing an
arbitrary number of concurrent readers, locking only the path of setting
up and clearing the cache.
This commit modifies the implementation of x509_get_ext_key_usage()
to not rely on mbedtls_asn1_get_sequence_of() but to instead use
mbedtls_asn1_traverse_sequence_of() with the same sequence-building
callback that also x509_get_subject_alt_name() uses, and which agrees
with the callback used by mbedtls_asn1_get_sequence_of().
The reason for this is that with this change, Mbed TLS itself isn't
using mbedtls_asn1_get_sequence_of() anymore, but only the more powerful
mbedtls_asn1_traverse_sequence_of(), so that unless application code
makes use of mbedtls_asn1_get_sequence_of(), its implementation
-- including the underlying sequence building callback -- will be
removed by link time garbage collection.
This commit introduces two static helpers
- `x509_buf_to_buf_raw()`
- `x509_buf_raw_to_buf()`
which convert to/from the old `mbedtls_x509_buf` and
the new `mbedtls_x509_buf_raw` (the latter omitting the
ASN.1 tag field).
So far, the CRT frame structure `mbedtls_x509_crt_frame` used
as `issuer_raw` and `subject_raw` the _content_ of the ASN.1
name structure for issuer resp. subject. This was in contrast
to the fields `issuer_raw` and `subject_raw` from the legacy
`mbedtls_x509_crt` structure, and caused some information
duplication by having both variants `xxx_no_hdr` and `xxx_with_hdr`
in `mbedtls_x509_crt` and `mbedtls_x509_crt_frame`.
This commit removes this mismatch by solely using the legacy
form of `issuer_raw` and `subject_raw`, i.e. those _including_
the ASN.1 name header.
Previously, `mbedtls_x509_crt_cache_provide_frame()` provided the requested
CRT frame by always parsing the raw data underlying the CRT. That's inefficient
in legacy mode, where the CRTs fields are permanently accessible through the
legacy `mbedtls_x509_crt` structure.
This commit modifies `mbedtls_x509_crt_cache_provide_frame()` in legacy mode
(that is, !MBEDTLS_X509_ON_DEMAND_PARSING) to setup the CRT frame by copying
fields from the legacy CRT structure.
This commit modifies the CRT parsing routine to flush
the CRT cache after parsing. More specifically, the
frame cache is flushed before the PK is parsed, to
avoid storing the PK and frame in RAM at the same time.
With the introduction of `mbedtls_x509_crt_get_{issuer|name}()`,
users need an easy way of freeing the dynamic name structures these
functions return.
To that end, this commit renames `x509_{sequence|name}_free()`
to `mbedtls_x509_{sequence|name}_free()` and gives them external linkage.
The legacy `mbedtls_x509_crt` contains fields `issuer/subject`
which are dynamically allocated linked list presentations of the
CRTs issuer and subject names, respectively.
The new CRT frame structure `mbedtls_x509_crt_frame`, however,
only provides pointers to the raw ASN.1 buffers for the issuer
and subject, for reasons of memory usage.
For convenience to users that previously used the `issuer`/`subject`
fields of `mbedtls_x509_crt`, this commit adds two public API functions
`mbedtls_x509_crt_get_subject()` and `mbedtls_x509_crt_get_issuer()`
which allow to request the legacy linked list presentation of the
CRTs subject / issuer names.
Similar to `mbedtls_x509_crt_get_pk()`, the returned names are owned
by the user, and must be freed through a call to `mbedtls_x509_name_free()`.
This commit unconditionally adds two convenience API functions:
- mbedtls_x509_crt_get_frame()
- mbedtls_x509_crt_get_pk()
which allow users to extract a CRT frame or PK context
from a certificate.
The difference with the existing acquire/release API for frame and PK
contexts is that in contrast to the latter, the structures returned by
the new API are owned by the user (and, in case of the PK context, need
to be freed by him). This makes the API easier to use, but comes at the
cost of additional memory overhead.
This commit replaces the dummy implementation of the CRT acquire/release
framework by a cache-based implementation which remembers frame and PK
associated to a CRT across multiple `acquire/release` pairs.
Access the peer's PK through the PK acquire/release API only.
Care has to be taken not to accidentally overwrite the return
value `ret` from the CRT chain verification.
This commit modifies the static function `x509_crt_verify_name()` to
use the acquire/release API to access the given CRTs `subject` field.
This function is solely called from the beginning of the CRT chain
verification routine, which also needs to access the child's CRT frame.
It should therefore be considered - for a later commit - to collapse
the two acquire/release pairs to one, thereby saving some code.
Previously, `mbedtls_x509_crt_der_internal()` used the `version` field
(which is `0` after initialization but strictly greater than 0 once a
CRT has successfully been parsed) to determine whether an
`mbedtls_x509_crt` instance had already been setup.
Preparating for the removal of `version` from the structure, this
commit modifies the code to instead peek at the raw data pointer,
which is NULL as long as the CRT structure hasn't been setup with a CRT,
and will be kept in the new CRT structure.
This commit adapts `mbedtls_x509_crt_info()` to no longer access
structure fields from `mbedtls_x509_crt` directly, but to instead
query for a `mbedtls_x509_crt_frame` and `mbedtls_pk_context` and
use these to extract the required CRT information.
This commit continues rewriting the CRT chain verification to use
the new acquire/release framework for CRTs. Specifically, it replaces
all member accesses of the current _parent_ CRT by accesses to the
respective frame.
This commit introduces an internal structure `mbedtls_x509_crt_sig_info`
containing all information that has to be kept from a child CRT when searching
for a potential parent:
- The issuer name
- The signature type
- The signature
- The hash of the CRT
The structure can be obtained from a CRT frame via `x509_crt_get_sig_info()`
and freed via `x509_crt_free_sig_info()`.
The purpose of this is to reduce the amount of RAM used during CRT
chain verification; once we've extracted the signature info structure
from the current child CRT, we can free all cached data for that CRT
(frame and PK) before searching for a suitable parent. This way, there
will ultimately not be more than one frame needed at a single point
during the verification.
The function `x509_crt_find_parent_in()` traverses a list of CRTs
to find a potential parent to a given CRT. So far, the logic was
the following: For each candidate,
- check basic parenting skills (mostly name match)
- verify signature
- verify validity
This order is insuitable for the new acquire/release layer of
indirection when dealing with CRTs, because we either have to
query the candidate's CRT frame twice, or query frame and PK
simultaneously.
This commit moves the validity check to the beginning of the
routine to allow querying for the frame and then for the PK.
The entry point for restartable ECC needs to be moved for that
to not forget the validity-flag while pausing ECC computations.
During CRT verification, `x509_crt_check_signature()` checks whether a
candidate parent CRT correctly signs the current child CRT.
This commit rewrites this function to use the new acquire/release
framework for using CRTs.
The goal of the subsequent commits is to remove all direct uses
of the existing `mbedtls_x509_crt` apart from the `raw` buffer
and the linked list `next` pointer.
The approach is the following: Whenever a code-path needs to inspect
a CRT, it can request a frame for the CRT through the API
`x509_crt_frame_acquire()`. On success, this function returns a pointer
to a frame structure for the CRT (the origin of which is flexible and
need not concern the caller) that can be used to inspect the desired
fields. Once done, the caller hands back the frame through an explicit
call to `x509_crt_frame_release()`.
This commit also adds an inefficient dummy implementation for
`x509_crt_frame_acquire()` which always allocates a new
`mbedtls_x509_crt_frame` structure on the heap and parses it
from the raw data underlying the CRT. This will change in subsequent
commits, but it constitutes a valid implementation to test against.
Ultimately, `x509_crt_frame_acquire()` is to compute a frame for the
given CRT only once, and cache it for subsequent calls.
The need for `x509_crt_frame_release()` is the following: When
implementing `x509_crt_frame_acquire()` through a flushable cache
as indicated above, it must be ensured that no thread destroys
a cached frame structure for the time it is needed by another
thread. The `acquire/release` pair allows to explicitly delimit
the lifetime requirements for the returned frame structure.
The frame pointer must not be used after the `release` call anymore;
and in fact, the dummy implementation shows that it would
immediately lead to a memory failure.
Analogously to `x509_crt_frame_{acquire|release}()`, there's also
`x509_crt_pk_{acquire|release}()` which allows to acquire/release
a PK context setup from the public key contained within the CRT.
This commit restructures the parsing of X.509 CRTs in the following way:
First, it introduces a 'frame' structure `mbedtls_x509_crt_frame`, which
contains pointers to some structured fields of a CRT as well as copies of
primitive fields. For example, there's a pointer-length pair delimiting the raw
public key data in the CRT, but there's a C-uint8 to store the CRT version
(not a pointer-length pair delimiting the ASN.1 structure holding the version).
Setting up a frame from a raw CRT buffer does not require any memory outside
of the frame structure itself; it's just attaches a 'template' to the buffer
that allows to inspect the structured parts of the CRT afterwards.
Note that the frame structure does not correspond to a particular ASN.1
structure; for example, it contains pointers to delimit the three parts
of a CRT (TBS, SignatureAlgorithm, Signature), but also pointers to the
fields of the TBS, and pointers into the Extensions substructure of the TBS.
Further, the commit introduces an internal function `x509_crt_parse_frame()`
which sets up a frame from a raw CRT buffer, as well as several small helper
functions which help setting up the more complex structures (Subject, Issuer, PK)
from the frame.
These functions are then put to use to rewrite the existing parsing function
`mbedtls_x509_crt_parse_der_core()` by setting up a CRT frame from the input
buffer, residing on the stack, and afterwards copying the respective fields
to the actual `mbedtls_x509_crt` structure and performing the deeper parsing
through the various helper functions.
At every occasion where we're using `mbedtls_x509_memcasecmp()` we're
checking that the two buffer lengths coincide before making the call.
This commit saves a few bytes of code by moving this length check
to `mbedtls_x509_memcasecmp()`.
This commit adds a new function `mbedtls_asn1_traverse_sequence_of()`
which traverses an ASN.1 SEQUENCE and calls a user-provided callback
for each entry.
It allows to put the following constraints on the tags allowed
in the SEQUENCE:
- A tag mask and mandatory tag value w.r.t. that mask.
A non-matching tag leads to an MBEDTLS_ERR_ASN1_UNEXPECTED_TAG error.
For example, it the mask if 0xFF, this means that only
a single tag will be allowed in the SEQUENCE.
- A tag mask and optional tag value w.r.t. that mask.
A non-matching tag is silently ignored.
The main use for this flexibility is the traversal of the
`SubjectAlternativeNames` extension, where some parts of the
tag are fixed but some are flexible to indicate which type
of name the entry describes.
