Add a new function mbedtls_asn1_write_named_bitstring() that removes
trailing 0s at the end of DER encoded bitstrings. The function is
implemented according to Hanno Becker's suggestions.
This commit also changes the functions x509write_crt_set_ns_cert_type
and crt_set_key_usage to call the new function as the use named
bitstrings instead of the regular bitstrings.
This commit duplicates the public function mbedtls_asn1_find_named_data()
defined in library/asn1parse.c within library/asn1write.c in order to
avoid a dependency of the ASN.1 writing module on the ASN.1 parsing module.
The duplication is unproblematic from a semantic and an efficiency
perspective becasue it is just a short list traversal that doesn't
actually do any ASN.1 parsing.
Fix IAR compiler warnings
Two warnings have been fixed:
1. code 'if( len <= 0xFFFFFFFF )' gave warning 'pointless integer comparison'.
This was fixed by wraping the condition in '#if SIZE_MAX > 0xFFFFFFFF'.
2. code 'diff |= A[i] ^ B[i];' gave warning 'the order of volatile accesses is undefined in'.
This was fixed by read the volatile data in temporary variables before the computation.
Explain IAR warning on volatile access
Consistent use of CMAKE_C_COMPILER_ID
In case an entry with the given OID already exists in the list passed to
mbedtls_asn1_store_named_data() and there is not enough memory to allocate
room for the new value, the existing entry will be freed but the preceding
entry in the list will sill hold a pointer to it. (And the following entries
in the list are no longer reachable.) This results in memory leak or a double
free.
The issue is we want to leave the list in a consistent state on allocation
failure. (We could add a warning that the list is left in inconsistent state
when the function returns NULL, but behaviour changes that require more care
from the user are undesirable, especially in a stable branch.)
The chosen solution is a bit inefficient in that there is a time where both
blocks are allocated, but at least it's safe and this should trump efficiency
here: this code is only used for generating certificates, which is unlikely to
be done on very constrained devices, or to be in the critical loop of
anything. Also, the sizes involved should be fairly small anyway.
fixes#367
* iotssl-519-asn1write-overflows-restricted:
Fix other int casts in bounds checking
Fix other occurrences of same bounds check issue
Fix potential buffer overflow in asn1write
In BER encoding, any boolean with a non-zero value is considered as
TRUE. However, DER encoding require a value of 255 (0xFF) for TRUE.
This commit makes `mbedtls_asn1_write_bool` function uses `255` instead
of `1` for BOOLEAN values.
With this fix, boolean values are now reconized by OS X keychain (tested
on OS X 10.11).
Fixes#318.
