Fix get_len_step when buffer_size==0. The intent of this test is to
ensure (via static or runtime buffer overflow analysis) that
mbedtls_asn1_get_len does not attempt to access beyond the end of the
buffer. When buffer_size is 0 (reached from get_len when parsing a
1-byte buffer), the buffer is buf[1..1] because allocating a 0-byte
buffer might yield a null pointer rather than a valid pointer. In this
case the end of the buffer is p==buf+1, not buf+buffer_size which is
buf+0.
The test passed because calling mbedtls_asn1_get_len(&p,end,...) with
end < p happens to work, but this is not guaranteed.
If Y was constructed through functions in this module, then Y->n == 0
iff Y->p == NULL. However we do not prevent filling mpi structures
manually, and zero may be represented with n=0 and p a valid pointer.
Most of the code can cope with such a representation, but for the
source of mbedtls_mpi_copy, this would cause an integer underflow.
Changing the test for zero from Y->p==NULL to Y->n==0 causes this case
to work at no extra cost.
If psa_mac_finish_internal fails (which can only happen due to bad
parameters or hardware problem), the error code was converted to
PSA_ERROR_INVALID_SIGNATURE if the uninitialized stack variable
actual_mac happened to contain the expected MAC. This is a minor bug
but it may be possible to leverage it as part of a longer attack path
in some scenarios.
Reported externally. Found by static analysis.
Before the initial seeding, reseed_counter used to always be 0. Now, the
value depends on whether or not the user has explicitly set the amount
of data to get from the nonce (via e.g.
mbedtls_ctr_drbg_set_nonce_len()). Add comments to clarify the possible
values reseed_counter can have before the initial seeding.
The library style is to start with the includes corresponding to the
current module and then the rest in alphabetical order. Some modules
have several header files (eg. ssl_internal.h).
The recently added error.h includes did not respect this convention and
this commit restores it. In some cases this is not possible just by
moving the error.h declarations. This commit fixes the pre-existing
order in these instances too.
Now that the Error module has error codes as well and is processed by
the generate_errors script like any other module, we don't need to
include the header manually.
One of the error codes was already reserved, this commit just makes it
explicit. The other one is a new error code for initializing return
values in the library: `MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED` should
not be returned by the library. If it is returned, then it is surely a
bug in the library or somebody is tampering with the device.
