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  • Alexander Færøy's avatar
    Use ((x + 7) >> 3) instead of (x >> 3) when converting from bits to bytes. · 7b2d1070
    Alexander Færøy authored
    This patch changes our bits-to-bytes conversion logic in the NSS
    implementation of `tor_tls_cert_matches_key()` from using (x >> 3) to
    ((x + 7) >> 3) since DER bit-strings are allowed to contain a number of
    bits that is not a multiple of 8.
    
    Additionally, we add a comment on why we cannot use the
    `DER_ConvertBitString()` macro from NSS, as we would potentially apply
    the bits-to-bytes conversion logic twice, which would lead to an
    insignificant amount of bytes being compared in
    `SECITEM_ItemsAreEqual()` and thus turn the logic into being a
    prefix match instead of a full match.
    
    The `DER_ConvertBitString()` macro is defined in NSS as:
    
        /*
        ** Macro to convert der decoded bit string into a decoded octet
        ** string. All it needs to do is fiddle with the length code.
        */
        #define DER_ConvertBitString(item)            \
            {                                         \
                (item)->len = ((item)->len + 7) >> 3; \
            }
    
    Thanks to Taylor Yu for spotting this problem.
    
    This patch is part of the fix for TROVE-2020-001.
    
    See: https://bugs.torproject.org/33119
    7b2d1070
tortls_nss.c 22.5 KB