Breaking into a series of statements makes things easier when stepping through
the code in a debugger.
Previous comments we stating the opposite or what the code tested for (what we
want vs what we're erroring out on) which was confusing.
Also expand a bit on the reasons for these restrictions.
ssl_get_next_record() may pend fatal alerts in response to receiving
invalid records. Previously, however, those were never actually sent
because there was no code-path checking for pending alerts.
This commit adds a call to ssl_send_pending_fatal_alert() after
the invocation of ssl_get_next_record() to fix this.
Modelled after the config-checking header from session s11n.
The list of relevant config flags was established by manually checking the
fields serialized in the format, and which config.h flags they depend on.
This probably deserves double-checking by reviewers.
Since the type of cid_len is unsigned but shorter than int, it gets
"promoted" to int (which is also the type of the result), unless we make the
other operand an unsigned int which then forces the expression to unsigned int
as well.
The number of meaning of the flags will be determined later, when handling the
relevant struct members. For now three bytes are reserved as an example, but
this number may change later.
This mainly follows the design document (saving all fields marked "saved" in
the main structure and the transform sub-structure) with two exceptions:
- things related to renegotiation are excluded here (there weren't quite in
the design document as the possibility of allowing renegotiation was still
on the table, which is no longer is) - also, ssl.secure_renegotiation (which
is not guarded by MBEDTLS_SSL_RENEGOTIATION because it's used in initial
handshakes even with renegotiation disabled) is still excluded, as we don't
need it after the handshake.
- things related to Connection ID are added, as they weren't present at the
time the design document was written.
The exact format of the header (value of the bitflag indicating compile-time
options, whether and how to merge it with the serialized session header) will
be determined later.
Enforce restrictions indicated in the documentation.
This allows to make some simplifying assumptions (no need to worry about
saving IVs for CBC in TLS < 1.1, nor about saving handshake data) and
guarantees that all values marked as "forced" in the design document have the
intended values and can be skipped when serialising.
Some of the "forced" values are not checked because their value is a
consequence of other checks (for example, session_negotiated == NULL outside
handshakes). We do however check that session and transform are not NULL (even
if that's also a consequence of the initial handshake being over) as we're
going to dereference them and static analyzers may appreciate the info.
At that point, the timer might not yet be configured.
The timer is reset at the following occasions:
- when it is initially configured through
mbedtls_ssl_set_timer_cb() or
mbedtls_ssl_set_timer_cb_cx()
- when a session is reset in mbedtls_ssl_session_reset()
- when a handshake finishes via mbedtls_ssl_handshake_wrap()
All modules using restartable ECC operations support passing `NULL`
as the restart context as a means to not use the feature.
The restart contexts for ECDSA and ECP are nested, and when calling
restartable ECP operations from restartable ECDSA operations, the
address of the ECP restart context to use is calculated by adding
the to the address of the ECDSA restart context the offset the of
the ECP restart context.
If the ECP restart context happens to not reside at offset `0`, this
leads to a non-`NULL` pointer being passed to restartable ECP
operations from restartable ECDSA-operations; those ECP operations
will hence assume that the pointer points to a valid ECP restart
address and likely run into a segmentation fault when trying to
dereference the non-NULL but close-to-NULL address.
The problem doesn't arise currently because luckily the ECP restart
context has offset 0 within the ECDSA restart context, but we should
not rely on it.
This commit fixes the passage from restartable ECDSA to restartable ECP
operations by propagating NULL as the restart context pointer.
Apart from being fragile, the previous version could also lead to
NULL pointer dereference failures in ASanDbg builds which dereferenced
the ECDSA restart context even though it's not needed to calculate the
address of the offset'ed ECP restart context.
This commit introduces the option MBEDTLS_SSL_CONF_SINGLE_HASH
which can be used to register a single supported signature hash
algorithm at compile time. It replaces the runtime configuration
API mbedtls_ssl_conf_sig_hashes() which allows to register a _list_
of supported signature hash algorithms.
In contrast to other options used to hardcode configuration options,
MBEDTLS_SSL_CONF_SINGLE_HASH isn't a numeric option, but instead it's
only relevant if it's defined or not. To actually set the single
supported hash algorithm that should be supported, numeric options
MBEDTLS_SSL_CONF_SINGLE_HASH_TLS_ID
MBEDTLS_SSL_CONF_SINGLE_HASH_MD_ID
must both be defined and provide the TLS ID and the Mbed TLS internal
ID and the chosen hash algorithm, respectively.
mbedtls_ssl_set_calc_verify_md() serves two purposes:
(a) It checks whether a hash algorithm is suitable to be used
in the CertificateVerify message.
(b) It updates the function callback pointing to the function that
computes handshake transcript for the CertificateVerify message
w.r.t. the chosen hash function.
Step (b) is only necessary when receiving the CertificateVerify
message, while writing the CertificateRequest only involves (a).
This commit modifies the writing code for the CertificateRequest
message to inline the check (a) and thereby avoiding the call to
mbedtls_ssl_calc_verify_md().
mbedtls_ssL_set_calc_verify_md() is used to select valid hashes when
writing the server's CertificateRequest message, as well as to verify
and act on the client's choice when reading its CertificateVerify
message.
If enabled at compile-time and configured via mbedtls_ssl_conf_sig_hashes()
the current code also offers SHA-1 in TLS 1.2. However, the SHA-1-based
handshake transcript in TLS 1.2 is different from the SHA-1 handshake
transcript used in TLS < 1.2, and we only maintain the latter
(through ssl_update_checksum_md5sha1()), but not the former.
Concretely, this will lead to CertificateVerify verification failure
if the client picks SHA-1 for the CertificateVerify message in a TLS 1.2
handshake.
This commit removes SHA-1 from the list of supported hashes in
the CertificateRequest message, and adapts two tests in ssl-opt.sh
which expect SHA-1 to be listed in the CertificateRequest message.
mbedtls_ssl_set_calc_verify_md() is only called from places
where it has been checked that TLS 1.2 is being used. The
corresponding compile-time and runtime guards checking the
version in mbedtls_ssl_set_calc_verify_md() are therefore
redundant and can be removed.
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().
