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Add additional validations based on X.690 rules

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The library was a tad bit fast and loose with respect to parsing some of the ASN.1 presented to it. It was kind of like we used Alternate Encoding Rules (AER), which was more relaxed than BER, CER or DER. This commit closes most of the gaps.

The changes are distantly related to Issue 346. Issue 346 caught a CVE bcause of the transient DoS. These fixes did not surface with negative effcts. Rather, the library was a bit too accomodating to the point it was not conforming
This commit is contained in:
Jeffrey Walton 2016-12-24 04:55:21 -05:00
parent 3475a235bf
commit b19332a69f
No known key found for this signature in database
GPG Key ID: B36AB348921B1838
2 changed files with 27 additions and 16 deletions
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11
asn.cpp
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@ -123,7 +123,7 @@ size_t BERDecodeOctetString(BufferedTransformation &bt, SecByteBlock &str)
size_t bc;
if (!BERLengthDecode(bt, bc))
BERDecodeError();
if (bc > bt.MaxRetrievable())
if (bc > bt.MaxRetrievable()) // Issue 346
BERDecodeError();
str.New(bc);
@ -141,7 +141,7 @@ size_t BERDecodeOctetString(BufferedTransformation &bt, BufferedTransformation &
size_t bc;
if (!BERLengthDecode(bt, bc))
BERDecodeError();
if (bc > bt.MaxRetrievable())
if (bc > bt.MaxRetrievable()) // Issue 346
BERDecodeError();
bt.TransferTo(str, bc);
@ -165,7 +165,7 @@ size_t BERDecodeTextString(BufferedTransformation &bt, std::string &str, byte as
size_t bc;
if (!BERLengthDecode(bt, bc))
BERDecodeError();
if (bc > bt.MaxRetrievable())
if (bc > bt.MaxRetrievable()) // Issue 346
BERDecodeError();
SecByteBlock temp(bc);
@ -196,11 +196,12 @@ size_t BERDecodeBitString(BufferedTransformation &bt, SecByteBlock &str, unsigne
BERDecodeError();
if (bc == 0)
BERDecodeError();
if (bc > bt.MaxRetrievable())
if (bc > bt.MaxRetrievable()) // Issue 346
BERDecodeError();
// X.690, 8.6.2.2: "The number [of unused bits] shall be in the range zero to seven"
byte unused;
if (!bt.Get(unused))
if (!bt.Get(unused) || unused > 7)
BERDecodeError();
unusedBits = unused;
str.resize(bc-1);

32
asn.h
View File

@ -55,13 +55,14 @@ enum ASNTag
//! \note These tags and flags are not complete
enum ASNIdFlag
{
UNIVERSAL = 0x00,
// DATA = 0x01,
// HEADER = 0x02,
CONSTRUCTED = 0x20,
APPLICATION = 0x40,
CONTEXT_SPECIFIC = 0x80,
PRIVATE = 0xc0
UNIVERSAL = 0x00,
// DATA = 0x01,
// HEADER = 0x02,
PRIMITIVE = 0x00,
CONSTRUCTED = 0x20,
APPLICATION = 0x40,
CONTEXT_SPECIFIC = 0x80,
PRIVATE = 0xc0
};
//! \brief Raises a BERDecodeErr
@ -478,9 +479,9 @@ size_t DEREncodeUnsigned(BufferedTransformation &out, T w, byte asnTag = INTEGER
}
//! \brief BER Decode unsigned value
//! \tparam T class or type
//! \tparam T fundamental C++ type
//! \param in BufferedTransformation object
//! \param w unsigned value to encode
//! \param w the decoded value
//! \param asnTag the ASN.1 type
//! \param minValue the minimum expected value
//! \param maxValue the maximum expected value
@ -488,7 +489,7 @@ size_t DEREncodeUnsigned(BufferedTransformation &out, T w, byte asnTag = INTEGER
//! \details DEREncodeUnsigned() can be used with INTEGER, BOOLEAN, and ENUM
template <class T>
void BERDecodeUnsigned(BufferedTransformation &in, T &w, byte asnTag = INTEGER,
T minValue = 0, T maxValue = ((std::numeric_limits<T>::max)()))
T minValue = 0, T maxValue = T(0xffffffff))
{
byte b;
if (!in.Get(b) || b != asnTag)
@ -498,7 +499,11 @@ void BERDecodeUnsigned(BufferedTransformation &in, T &w, byte asnTag = INTEGER,
bool definite = BERLengthDecode(in, bc);
if (!definite)
BERDecodeError();
if (bc > in.MaxRetrievable())
if (bc > in.MaxRetrievable()) // Issue 346
BERDecodeError();
if (asnTag == BOOLEAN && bc != 1) // X.690, 8.2.1
BERDecodeError();
if ((asnTag == INTEGER || asnTag == ENUMERATED) && bc == 0) // X.690, 8.3.1 and 8.4
BERDecodeError();
SecByteBlock buf(bc);
@ -506,6 +511,11 @@ void BERDecodeUnsigned(BufferedTransformation &in, T &w, byte asnTag = INTEGER,
if (bc != in.Get(buf, bc))
BERDecodeError();
// This consumes leading 0 octets. According to X.690, 8.3.2, it could be non-conforming behavior.
// X.690, 8.3.2 says "the bits of the first octet and bit 8 of the second octet ... (a) shall
// not all be ones and (b) shall not all be zeros ... These rules ensure that an integer value
// is always encoded in the smallest possible number of octet".
// We invented AER (Alternate Encoding Rules), which is more relaxed than BER, CER, and DER.
const byte *ptr = buf;
while (bc > sizeof(w) && *ptr == 0)
{