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Fix buffer overread in mbedtls_x509_get_time()

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A heap overread might happen when parsing malformed certificates.
Reported by Peng Li and Yueh-Hsun Lin.

Refactoring the parsing fixes the problem. This commit applies the
relevant part of the OpenVPN contribution applied to mbed TLS 1.3
in commit 17da9dd829.
This commit is contained in:
Janos Follath 2017-02-03 12:36:59 +00:00 committed by Simon Butcher
parent ea7054a00c
commit 87c980749d
2 changed files with 88 additions and 51 deletions
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2
ChangeLog
View File

@ -40,6 +40,8 @@ Bugfix
cause buffer bound checks to be bypassed. Found by Eyal Itkin.
* Fixed potential arithmetic overflow in mbedtls_base64_decode() that could
cause buffer bound checks to be bypassed. Found by Eyal Itkin.
* Fixed heap overreads in mbedtls_x509_get_time(). Found by Peng
Li/Yueh-Hsun Lin, KNOX Security, Samsung Research America.
= mbed TLS 2.4.1 branch released 2016-12-13

137
library/x509.c
View File

@ -480,14 +480,20 @@ int mbedtls_x509_get_name( unsigned char **p, const unsigned char *end,
}
}
static int x509_parse_int(unsigned char **p, unsigned n, int *res){
static int x509_parse_int( unsigned char **p, size_t n, int *res )
{
*res = 0;
for( ; n > 0; --n ){
if( ( **p < '0') || ( **p > '9' ) ) return MBEDTLS_ERR_X509_INVALID_DATE;
for( ; n > 0; --n )
{
if( ( **p < '0') || ( **p > '9' ) )
return ( MBEDTLS_ERR_X509_INVALID_DATE );
*res *= 10;
*res += (*(*p)++ - '0');
*res += ( *(*p)++ - '0' );
}
return 0;
return( 0 );
}
static int x509_date_is_valid(const mbedtls_x509_time *time)
@ -517,6 +523,70 @@ static int x509_date_is_valid(const mbedtls_x509_time *time)
return( 0 );
}
/*
* Parse an ASN1_UTC_TIME (yearlen=2) or ASN1_GENERALIZED_TIME (yearlen=4)
* field.
*/
static int x509_parse_time( unsigned char **p, size_t len, size_t yearlen,
mbedtls_x509_time *time )
{
int ret;
/*
* Minimum length is 10 or 12 depending on yearlen
*/
if ( len < yearlen + 8 )
return ( MBEDTLS_ERR_X509_INVALID_DATE );
len -= yearlen + 8;
/*
* Parse year, month, day, hour, minute
*/
CHECK( x509_parse_int( p, yearlen, &time->year ) );
if ( 2 == yearlen )
{
if ( time->year < 50 )
time->year += 100;
time->year += 1900;
}
CHECK( x509_parse_int( p, 2, &time->mon ) );
CHECK( x509_parse_int( p, 2, &time->day ) );
CHECK( x509_parse_int( p, 2, &time->hour ) );
CHECK( x509_parse_int( p, 2, &time->min ) );
/*
* Parse seconds if present
*/
if ( len >= 2 )
{
CHECK( x509_parse_int( p, 2, &time->sec ) );
len -= 2;
}
else
return ( MBEDTLS_ERR_X509_INVALID_DATE );
/*
* Parse trailing 'Z' if present
*/
if ( 1 == len && 'Z' == **p )
{
(*p)++;
len--;
}
/*
* We should have parsed all characters at this point
*/
if ( 0 != len )
return ( MBEDTLS_ERR_X509_INVALID_DATE );
CHECK( x509_date_is_valid( time ) );
return ( 0 );
}
/*
* Time ::= CHOICE {
* utcTime UTCTime,
@ -526,7 +596,7 @@ int mbedtls_x509_get_time( unsigned char **p, const unsigned char *end,
mbedtls_x509_time *time )
{
int ret;
size_t len;
size_t len, year_len;
unsigned char tag;
if( ( end - *p ) < 1 )
@ -536,55 +606,20 @@ int mbedtls_x509_get_time( unsigned char **p, const unsigned char *end,
tag = **p;
if( tag == MBEDTLS_ASN1_UTC_TIME )
{
(*p)++;
ret = mbedtls_asn1_get_len( p, end, &len );
if( ret != 0 )
return( MBEDTLS_ERR_X509_INVALID_DATE + ret );
CHECK( x509_parse_int( p, 2, &time->year ) );
CHECK( x509_parse_int( p, 2, &time->mon ) );
CHECK( x509_parse_int( p, 2, &time->day ) );
CHECK( x509_parse_int( p, 2, &time->hour ) );
CHECK( x509_parse_int( p, 2, &time->min ) );
if( len > 10 )
CHECK( x509_parse_int( p, 2, &time->sec ) );
if( len > 12 && *(*p)++ != 'Z' )
return( MBEDTLS_ERR_X509_INVALID_DATE );
time->year += 100 * ( time->year < 50 );
time->year += 1900;
CHECK( x509_date_is_valid( time ) );
return( 0 );
}
year_len = 2;
else if( tag == MBEDTLS_ASN1_GENERALIZED_TIME )
{
(*p)++;
ret = mbedtls_asn1_get_len( p, end, &len );
if( ret != 0 )
return( MBEDTLS_ERR_X509_INVALID_DATE + ret );
CHECK( x509_parse_int( p, 4, &time->year ) );
CHECK( x509_parse_int( p, 2, &time->mon ) );
CHECK( x509_parse_int( p, 2, &time->day ) );
CHECK( x509_parse_int( p, 2, &time->hour ) );
CHECK( x509_parse_int( p, 2, &time->min ) );
if( len > 12 )
CHECK( x509_parse_int( p, 2, &time->sec ) );
if( len > 14 && *(*p)++ != 'Z' )
return( MBEDTLS_ERR_X509_INVALID_DATE );
CHECK( x509_date_is_valid( time ) );
return( 0 );
}
year_len = 4;
else
return( MBEDTLS_ERR_X509_INVALID_DATE +
MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
(*p)++;
ret = mbedtls_asn1_get_len( p, end, &len );
if( ret != 0 )
return( MBEDTLS_ERR_X509_INVALID_DATE + ret );
return x509_parse_time( p, len, year_len, time );
}
int mbedtls_x509_get_sig( unsigned char **p, const unsigned char *end, mbedtls_x509_buf *sig )