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.
This commit adds a callback for use with `x509_subject_alt_name_traverse()`
which builds the legacy dynamically allocated linked list presentation
of the `SubjectAlternativeNames` extension while traversing the raw data.
The current CN name verification x509_crt_verify_name() traverses
the dynamically allocated linked list presentation of the subject
alternative name extension, searching for an alternative name that
matches the desired hostname configured by the application.
Eventually, we want to remove this dynamically allocated linked list
for the benefit of reduced code size and RAM usage, and hence need to
rewrite x509_crt_verify_name() in a way that builds on the raw ASN.1
buffer holding the SubjectAlternativeNames extension.
This commit does this by using the existing SubjectAlternativeNames
traversal routine x509_subject_alt_name_traverse(), passing to it a
callback which compares the current alternative name component to the
desired hostname configured by the application.
This commit adds a new function `x509_subject_alt_name_traverse()`
which allows to traverse the raw ASN.1 data of a `SubjectAlternativeNames`
extension.
The `SubjectAlternativeNames` extension needs to be traversed
in the following situations:
1 Initial traversal to check well-formedness of ASN.1 data
2 Traversal to check for a particular name component
3 Building the legacy linked list presentation
Analogously to how multiple tasks related to X.509 name comparison
are implemented through the workhorse `mbedtlS_x509_name_cmp_raw()`,
the new function `x509_subject_alt_name_traverse()` allows to pass
an arbitrary callback which is called on any component of the
`SubjectAlternativeNames` extension found. This way, the above
three tasks can be implemented by passing
1 a NULL callback,
2 a name comparison callback
3 a linked list building callback.
In preparation for rewriting the `SubjectAlternativeName` search routine
to use raw ASN.1 data, this commit changes `x509_check_wildcard()` and
`x509_check_cn()`, responsible for checking whether a name matches a
wildcard pattern, to take a raw buffer pointer and length as parameters
instead of an `mbedtls_x509_buf` instance.
This is analogous to a previous commit for the `ExtendedKeyUsage`
extension: We aim at not using dynamically allocated linked lists
to represent the components of the `SubjectAlternativeName` extension,
but to traverse the raw ASN.1 data when needed.
This commit adds a field to `mbedtls_x509_crt` containing the raw
ASN.1 buffer bounds of the `SubjectAlternativeNames` extension.
This commit re-implements `mbedtls_x509_crt_check_extended_key_usage()`
to not use the dynamically allocated linked list presentation of the
`ExtendedKeyUsage` but to search for the required usage by traversing
the raw ASN.1 data.
The previous commits replace the use of dynamically allocated linked lists
for X.509 name inspection. This commit is the first in a series which attempts
the same for the `ExtendedKeyUsage` extension. So far, when a CRT is parsed,
the extension is traversed and converted into a dynamically allocated linked
list, which is then search through whenever the usage of a CRT needs to be
checked through `mbedtls_x509_check_extended_key_usage()`.
As a first step, this commit introduces a raw buffer holding the bounds
of the `ExtendedKeyUsage` extension to the `mbedtls_x509_crt` structure.
The previous CN name comparison function x509_crt_verify_name()
traversed the dynamically allocated linked list presentation of
the CRT's subject, comparing each entry to the desired hostname
configured by the application code.
Eventually, we want to get rid of the linked list presentation of
the CRT's subject to save both code and RAM usage, and hence need
to rewrite the CN verification routine in a way that builds on the
raw ASN.1 subject data only.
In order to avoid duplicating the code for the parsing of the nested
ASN.1 name structure, this commit performs the name search by using
the existing name traversal function mbedtls_x509_name_cmp_raw(),
passing to it a callback which checks whether the current name
component matches the desired hostname.
There are three operations that need to be performed on an X.509 name:
1 Initial traversal to check well-formedness of the ASN.1 structure.
2 Comparison between two X.509 name sequences.
3 Checking whether an X.509 name matches a client's ServerName request.
Each of these tasks involves traversing the nested ASN.1 structure,
In the interest of saving code, we aim to provide a single function
which can perform all of the above tasks.
The existing comparison function is already suitable not only for task 2,
but also for 1: One can simply pass two equal ASN.1 name buffers, in which
case the function will succeed if and only if that buffer is a well-formed
ASN.1 name.
This commit further adds a callback to `mbedtls_x509_name_cmp_raw()` which
is called after each successful step in the simultaneous name traversal and
comparison; it may perform any operation on the current name and potentially
signal that the comparison should be aborted.
With that, task 3 can be implemented by passing equal names and a callback
which aborts as soon as it finds the desired name component.
This commit replaces the previous calls to `mbedtls_x509_name_cmp()`
during CRT verification (to match child and parent, to check whether
a CRT is self-issued, and to match CRLs and CAs) by calls to the new
`mbedtls_x509_name_cmp_raw()` using the raw ASN.1 data; it passes the
raw buffers introduced in the last commits.
The previous name comparison function mbedtls_x509_name_cmp() is now
both unused and unneeded, and is removed.
To make use of the X.509 name comparison function based on raw
ASN.1 data that was introduced in the previous commit, this commit
adds an ASN.1 buffer field `issuer_raw_no_hdr` to `mbedtls_x509_crl`
which delimits the raw contents of the CRLs `Issuer` field.
The previous field `issuer_raw` isn't suitable for that because
it includes the ASN.1 header.
This commit provides a new function `mbedtls_x509_name_cmp_raw()`
to x509.c for comparing to X.509 names by traversing the raw ASN.1
data (as opposed to using the dynamically allocated linked list
of `mbedtls_x509_name` structures). It has external linkage because
it will be needed in `x509_crt` and `x509_crl`, but is marked
internal and hence not part of the public API.
The function `mbedtls_x509_sig_alg_gets()` previously needed the
raw ASN.1 OID string even though it is implicit in the PK and MD
parameters.
This commit modifies `mbedtls_x509_sig_alg_gets()` to infer the OID
and remove it from the parameters.
This will be needed for the new X.509 CRT structure which will
likely not store the signature OID.
Care has to be taken to handle the case of RSASSA-PSS correctly,
where the hash algorithm in the OID list is set to MBEDTLS_MD_NONE
because it's only determined by the algorithm parameters.
The previous code
- checked that at least 1 byte of ASN.1 tag data is available,
- read and stored that ASN.1 tag,
- called the ASN.1 parsing function, part of which is checking
that enough space is available and that the ASN.1 tag matches
the expected value MBEDTLS_ASN1_OID.
Since the ASN.1 parsing function includes bounds checks,
this can be streamlined to:
- call the ASN.1 parsing function directly,
- on success, store MBEDTLS_ASN1_OID in the tag field.
This commit applies this simplification to mbedtls_asn1_get_alg().
Consider the following code-template:
int beef();
static int foo()
{
/* ... */
ret = beef();
if( ret != 0 )
return( ret + HIGH_LEVEL );
/* ... */
}
int bar()
{
/* ... */
ret = foo();
if( ret != 0 )
...
/* ... */
}
This leads to slightly larger code than expected, because when the
compiler inlines foo() into bar(), the sequence of return sequences
cannot be squashed, because compiler might not have knowledge that
the wrapping `ret + HIGH_LEVEL` of the return value of beef() doesn't
lead to foo() returning 0.
This can be avoided by performing error code wrapping in nested
functions calls at the top of the call chain.
This commit applies this slight optimization to mbedtls_x509_get_name().
It also moves various return statements into a single exit section,
again with the intend to save code.
