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mbedtls_asn1_get_int: explain the logic

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No behavior change.
This commit is contained in:
Gilles Peskine 2019-10-10 19:27:53 +02:00
parent 0370b1bd7d
commit 9fd9794d10
1 changed files with 9 additions and 1 deletions
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10
library/asn1parse.c
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@ -149,14 +149,22 @@ int mbedtls_asn1_get_int( unsigned char **p,
if( ( ret = mbedtls_asn1_get_tag( p, end, &len, MBEDTLS_ASN1_INTEGER ) ) != 0 ) if( ( ret = mbedtls_asn1_get_tag( p, end, &len, MBEDTLS_ASN1_INTEGER ) ) != 0 )
return( ret ); return( ret );
if( len == 0 || ( **p & 0x80 ) != 0 ) /* len==0 is malformed (0 must be represented as 020100). */
if( len == 0 )
return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );
/* This is a cryptography library. Reject negative integers. */
if( ( **p & 0x80 ) != 0 )
return( MBEDTLS_ERR_ASN1_INVALID_LENGTH ); return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );
/* Skip leading zeros. */
while( len > 0 && **p == 0 ) while( len > 0 && **p == 0 )
{ {
++( *p ); ++( *p );
--len; --len;
} }
/* Reject integers that don't fit in an int. This code assumes that
* the int type has no padding bit. */
if( len > sizeof( int ) ) if( len > sizeof( int ) )
return( MBEDTLS_ERR_ASN1_INVALID_LENGTH ); return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );