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Merge remote-tracking branch 'restricted/pr/495' into mbedtls-2.1

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Simon Butcher 2018-07-24 23:42:13 +01:00
commit 3339fe9a02
6 changed files with 257 additions and 81 deletions
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33
ChangeLog
View File

@ -2,6 +2,39 @@ mbed TLS ChangeLog (Sorted per branch, date)
= mbed TLS x.x.x branch released xxxx-xx-xx
Security
* Fix a vulnerability in TLS ciphersuites based on CBC and using SHA-384,
in (D)TLS 1.0 to 1.2, that allowed an active network attacker to
partially recover the plaintext of messages under some conditions by
exploiting timing measurements. With DTLS, the attacker could perform
this recovery by sending many messages in the same connection. With TLS
or if mbedtls_ssl_conf_dtls_badmac_limit() was used, the attack only
worked if the same secret (for example a HTTP Cookie) has been repeatedly
sent over connections manipulated by the attacker. Connections using GCM
or CCM instead of CBC, using hash sizes other than SHA-384, or using
Encrypt-then-Mac (RFC 7366) were not affected. The vulnerability was
caused by a miscalculation (for SHA-384) in a countermeasure to the
original Lucky 13 attack. Found by Kenny Paterson, Eyal Ronen and Adi
Shamir.
* Fix a vulnerability in TLS ciphersuites based on CBC, in (D)TLS 1.0 to
1.2, that allowed a local attacker, able to execute code on the local
machine as well as manipulate network packets, to partially recover the
plaintext of messages under some conditions by using a cache attack
targetting an internal MD/SHA buffer. With TLS or if
mbedtls_ssl_conf_dtls_badmac_limit() was used, the attack only worked if
the same secret (for example a HTTP Cookie) has been repeatedly sent over
connections manipulated by the attacker. Connections using GCM or CCM
instead of CBC or using Encrypt-then-Mac (RFC 7366) were not affected.
Found by Kenny Paterson, Eyal Ronen and Adi Shamir.
* Add a counter-measure against a vulnerability in TLS ciphersuites based
on CBC, in (D)TLS 1.0 to 1.2, that allowed a local attacker, able to
execute code on the local machine as well as manipulate network packets,
to partially recover the plaintext of messages under some conditions (see
previous entry) by using a cache attack targeting the SSL input record
buffer. Connections using GCM or CCM instead of CBC or using
Encrypt-then-Mac (RFC 7366) were not affected. Found by Kenny Paterson,
Eyal Ronen and Adi Shamir.
Bugfix
* Fix compilation error on C++, because of a variable named new.
Found and fixed by Hirotaka Niisato in #1783.

49
library/md5.c
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@ -275,36 +275,51 @@ void mbedtls_md5_update( mbedtls_md5_context *ctx, const unsigned char *input, s
}
}
static const unsigned char md5_padding[64] =
{
0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};
/*
* MD5 final digest
*/
void mbedtls_md5_finish( mbedtls_md5_context *ctx, unsigned char output[16] )
{
uint32_t last, padn;
uint32_t used;
uint32_t high, low;
unsigned char msglen[8];
/*
* Add padding: 0x80 then 0x00 until 8 bytes remain for the length
*/
used = ctx->total[0] & 0x3F;
ctx->buffer[used++] = 0x80;
if( used <= 56 )
{
/* Enough room for padding + length in current block */
memset( ctx->buffer + used, 0, 56 - used );
}
else
{
/* We'll need an extra block */
memset( ctx->buffer + used, 0, 64 - used );
mbedtls_md5_process( ctx, ctx->buffer );
memset( ctx->buffer, 0, 56 );
}
/*
* Add message length
*/
high = ( ctx->total[0] >> 29 )
| ( ctx->total[1] << 3 );
low = ( ctx->total[0] << 3 );
PUT_UINT32_LE( low, msglen, 0 );
PUT_UINT32_LE( high, msglen, 4 );
PUT_UINT32_LE( low, ctx->buffer, 56 );
PUT_UINT32_LE( high, ctx->buffer, 60 );
last = ctx->total[0] & 0x3F;
padn = ( last < 56 ) ? ( 56 - last ) : ( 120 - last );
mbedtls_md5_update( ctx, md5_padding, padn );
mbedtls_md5_update( ctx, msglen, 8 );
mbedtls_md5_process( ctx, ctx->buffer );
/*
* Output final state
*/
PUT_UINT32_LE( ctx->state[0], output, 0 );
PUT_UINT32_LE( ctx->state[1], output, 4 );
PUT_UINT32_LE( ctx->state[2], output, 8 );

49
library/sha1.c
View File

@ -307,36 +307,51 @@ void mbedtls_sha1_update( mbedtls_sha1_context *ctx, const unsigned char *input,
memcpy( (void *) (ctx->buffer + left), input, ilen );
}
static const unsigned char sha1_padding[64] =
{
0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};
/*
* SHA-1 final digest
*/
void mbedtls_sha1_finish( mbedtls_sha1_context *ctx, unsigned char output[20] )
{
uint32_t last, padn;
uint32_t used;
uint32_t high, low;
unsigned char msglen[8];
/*
* Add padding: 0x80 then 0x00 until 8 bytes remain for the length
*/
used = ctx->total[0] & 0x3F;
ctx->buffer[used++] = 0x80;
if( used <= 56 )
{
/* Enough room for padding + length in current block */
memset( ctx->buffer + used, 0, 56 - used );
}
else
{
/* We'll need an extra block */
memset( ctx->buffer + used, 0, 64 - used );
mbedtls_sha1_process( ctx, ctx->buffer );
memset( ctx->buffer, 0, 56 );
}
/*
* Add message length
*/
high = ( ctx->total[0] >> 29 )
| ( ctx->total[1] << 3 );
low = ( ctx->total[0] << 3 );
PUT_UINT32_BE( high, msglen, 0 );
PUT_UINT32_BE( low, msglen, 4 );
PUT_UINT32_BE( high, ctx->buffer, 56 );
PUT_UINT32_BE( low, ctx->buffer, 60 );
last = ctx->total[0] & 0x3F;
padn = ( last < 56 ) ? ( 56 - last ) : ( 120 - last );
mbedtls_sha1_update( ctx, sha1_padding, padn );
mbedtls_sha1_update( ctx, msglen, 8 );
mbedtls_sha1_process( ctx, ctx->buffer );
/*
* Output final state
*/
PUT_UINT32_BE( ctx->state[0], output, 0 );
PUT_UINT32_BE( ctx->state[1], output, 4 );
PUT_UINT32_BE( ctx->state[2], output, 8 );

49
library/sha256.c
View File

@ -273,36 +273,51 @@ void mbedtls_sha256_update( mbedtls_sha256_context *ctx, const unsigned char *in
memcpy( (void *) (ctx->buffer + left), input, ilen );
}
static const unsigned char sha256_padding[64] =
{
0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};
/*
* SHA-256 final digest
*/
void mbedtls_sha256_finish( mbedtls_sha256_context *ctx, unsigned char output[32] )
{
uint32_t last, padn;
uint32_t used;
uint32_t high, low;
unsigned char msglen[8];
/*
* Add padding: 0x80 then 0x00 until 8 bytes remain for the length
*/
used = ctx->total[0] & 0x3F;
ctx->buffer[used++] = 0x80;
if( used <= 56 )
{
/* Enough room for padding + length in current block */
memset( ctx->buffer + used, 0, 56 - used );
}
else
{
/* We'll need an extra block */
memset( ctx->buffer + used, 0, 64 - used );
mbedtls_sha256_process( ctx, ctx->buffer );
memset( ctx->buffer, 0, 56 );
}
/*
* Add message length
*/
high = ( ctx->total[0] >> 29 )
| ( ctx->total[1] << 3 );
low = ( ctx->total[0] << 3 );
PUT_UINT32_BE( high, msglen, 0 );
PUT_UINT32_BE( low, msglen, 4 );
PUT_UINT32_BE( high, ctx->buffer, 56 );
PUT_UINT32_BE( low, ctx->buffer, 60 );
last = ctx->total[0] & 0x3F;
padn = ( last < 56 ) ? ( 56 - last ) : ( 120 - last );
mbedtls_sha256_update( ctx, sha256_padding, padn );
mbedtls_sha256_update( ctx, msglen, 8 );
mbedtls_sha256_process( ctx, ctx->buffer );
/*
* Output final state
*/
PUT_UINT32_BE( ctx->state[0], output, 0 );
PUT_UINT32_BE( ctx->state[1], output, 4 );
PUT_UINT32_BE( ctx->state[2], output, 8 );

53
library/sha512.c
View File

@ -302,40 +302,51 @@ void mbedtls_sha512_update( mbedtls_sha512_context *ctx, const unsigned char *in
memcpy( (void *) (ctx->buffer + left), input, ilen );
}
static const unsigned char sha512_padding[128] =
{
0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
};
/*
* SHA-512 final digest
*/
void mbedtls_sha512_finish( mbedtls_sha512_context *ctx, unsigned char output[64] )
{
size_t last, padn;
unsigned used;
uint64_t high, low;
unsigned char msglen[16];
/*
* Add padding: 0x80 then 0x00 until 16 bytes remain for the length
*/
used = ctx->total[0] & 0x7F;
ctx->buffer[used++] = 0x80;
if( used <= 112 )
{
/* Enough room for padding + length in current block */
memset( ctx->buffer + used, 0, 112 - used );
}
else
{
/* We'll need an extra block */
memset( ctx->buffer + used, 0, 128 - used );
mbedtls_sha512_process( ctx, ctx->buffer );
memset( ctx->buffer, 0, 112 );
}
/*
* Add message length
*/
high = ( ctx->total[0] >> 61 )
| ( ctx->total[1] << 3 );
low = ( ctx->total[0] << 3 );
PUT_UINT64_BE( high, msglen, 0 );
PUT_UINT64_BE( low, msglen, 8 );
PUT_UINT64_BE( high, ctx->buffer, 112 );
PUT_UINT64_BE( low, ctx->buffer, 120 );
last = (size_t)( ctx->total[0] & 0x7F );
padn = ( last < 112 ) ? ( 112 - last ) : ( 240 - last );
mbedtls_sha512_update( ctx, sha512_padding, padn );
mbedtls_sha512_update( ctx, msglen, 16 );
mbedtls_sha512_process( ctx, ctx->buffer );
/*
* Output final state
*/
PUT_UINT64_BE( ctx->state[0], output, 0 );
PUT_UINT64_BE( ctx->state[1], output, 8 );
PUT_UINT64_BE( ctx->state[2], output, 16 );

105
library/ssl_tls.c
View File

@ -1260,6 +1260,27 @@ static void ssl_mac( mbedtls_md_context_t *md_ctx,
#define SSL_SOME_MODES_USE_MAC
#endif
/* The function below is only used in the Lucky 13 counter-measure in
* ssl_decrypt_buf(). These are the defines that guard the call site. */
#if defined(SSL_SOME_MODES_USE_MAC) && \
( defined(MBEDTLS_SSL_PROTO_TLS1) || \
defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
defined(MBEDTLS_SSL_PROTO_TLS1_2) )
/* This function makes sure every byte in the memory region is accessed
* (in ascending addresses order) */
static void ssl_read_memory( unsigned char *p, size_t len )
{
unsigned char acc = 0;
volatile unsigned char force;
for( ; len != 0; p++, len-- )
acc ^= *p;
force = acc;
(void) force;
}
#endif /* SSL_SOME_MODES_USE_MAC && ( TLS1 || TLS1_1 || TLS1_2 ) */
/*
* Encryption/decryption functions
*/
@ -1935,8 +1956,10 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl )
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
#if defined(MBEDTLS_SSL_DEBUG_ALL)
MBEDTLS_SSL_DEBUG_BUF( 4, "raw buffer after decryption",
ssl->in_msg, ssl->in_msglen );
#endif
/*
* Authenticate if not done yet.
@ -1969,20 +1992,69 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl )
{
/*
* Process MAC and always update for padlen afterwards to make
* total time independent of padlen
*
* extra_run compensates MAC check for padlen
* total time independent of padlen.
*
* Known timing attacks:
* - Lucky Thirteen (http://www.isg.rhul.ac.uk/tls/TLStiming.pdf)
*
* We use ( ( Lx + 8 ) / 64 ) to handle 'negative Lx' values
* correctly. (We round down instead of up, so -56 is the correct
* value for our calculations instead of -55)
* To compensate for different timings for the MAC calculation
* depending on how much padding was removed (which is determined
* by padlen), process extra_run more blocks through the hash
* function.
*
* The formula in the paper is
* extra_run = ceil( (L1-55) / 64 ) - ceil( (L2-55) / 64 )
* where L1 is the size of the header plus the decrypted message
* plus CBC padding and L2 is the size of the header plus the
* decrypted message. This is for an underlying hash function
* with 64-byte blocks.
* We use ( (Lx+8) / 64 ) to handle 'negative Lx' values
* correctly. We round down instead of up, so -56 is the correct
* value for our calculations instead of -55.
*
* Repeat the formula rather than defining a block_size variable.
* This avoids requiring division by a variable at runtime
* (which would be marginally less efficient and would require
* linking an extra division function in some builds).
*/
size_t j, extra_run = 0;
extra_run = ( 13 + ssl->in_msglen + padlen + 8 ) / 64 -
( 13 + ssl->in_msglen + 8 ) / 64;
/*
* The next two sizes are the minimum and maximum values of
* in_msglen over all padlen values.
*
* They're independent of padlen, since we previously did
* in_msglen -= padlen.
*
* Note that max_len + maclen is never more than the buffer
* length, as we previously did in_msglen -= maclen too.
*/
const size_t max_len = ssl->in_msglen + padlen;
const size_t min_len = ( max_len > 256 ) ? max_len - 256 : 0;
switch( ssl->transform_in->ciphersuite_info->mac )
{
#if defined(MBEDTLS_MD5_C) || defined(MBEDTLS_SHA1_C) || \
defined(MBEDTLS_SHA256_C)
case MBEDTLS_MD_MD5:
case MBEDTLS_MD_SHA1:
case MBEDTLS_MD_SHA256:
/* 8 bytes of message size, 64-byte compression blocks */
extra_run = ( 13 + ssl->in_msglen + padlen + 8 ) / 64 -
( 13 + ssl->in_msglen + 8 ) / 64;
break;
#endif
#if defined(MBEDTLS_SHA512_C)
case MBEDTLS_MD_SHA384:
/* 16 bytes of message size, 128-byte compression blocks */
extra_run = ( 13 + ssl->in_msglen + padlen + 16 ) / 128 -
( 13 + ssl->in_msglen + 16 ) / 128;
break;
#endif
default:
MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
extra_run &= correct * 0xFF;
@ -1991,12 +2063,25 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl )
mbedtls_md_hmac_update( &ssl->transform_in->md_ctx_dec, ssl->in_len, 2 );
mbedtls_md_hmac_update( &ssl->transform_in->md_ctx_dec, ssl->in_msg,
ssl->in_msglen );
/* Make sure we access everything even when padlen > 0. This
* makes the synchronisation requirements for just-in-time
* Prime+Probe attacks much tighter and hopefully impractical. */
ssl_read_memory( ssl->in_msg + ssl->in_msglen, padlen );
mbedtls_md_hmac_finish( &ssl->transform_in->md_ctx_dec, mac_expect );
/* Call mbedtls_md_process at least once due to cache attacks */
/* Call mbedtls_md_process at least once due to cache attacks
* that observe whether md_process() was called of not */
for( j = 0; j < extra_run + 1; j++ )
mbedtls_md_process( &ssl->transform_in->md_ctx_dec, ssl->in_msg );
mbedtls_md_hmac_reset( &ssl->transform_in->md_ctx_dec );
/* Make sure we access all the memory that could contain the MAC,
* before we check it in the next code block. This makes the
* synchronisation requirements for just-in-time Prime+Probe
* attacks much tighter and hopefully impractical. */
ssl_read_memory( ssl->in_msg + min_len,
max_len - min_len + ssl->transform_in->maclen );
}
else
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
@ -2006,9 +2091,11 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl )
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
#if defined(MBEDTLS_SSL_DEBUG_ALL)
MBEDTLS_SSL_DEBUG_BUF( 4, "expected mac", mac_expect, ssl->transform_in->maclen );
MBEDTLS_SSL_DEBUG_BUF( 4, "message mac", ssl->in_msg + ssl->in_msglen,
ssl->transform_in->maclen );
#endif
if( mbedtls_ssl_safer_memcmp( ssl->in_msg + ssl->in_msglen, mac_expect,
ssl->transform_in->maclen ) != 0 )