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Fix NULL+0 undefined behavior in ECB encryption and decryption

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psa_cipher_encrypt() and psa_cipher_decrypt() sometimes add a zero offset to
a null pointer when the cipher does not use an IV. This is undefined
behavior, although it works as naively expected on most platforms. This
can cause a crash with modern Clang+ASan (depending on compiler optimizations).

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2022-11-23 14:15:57 +01:00
parent 1d1d53622f
commit 42649d9270
5 changed files with 58 additions and 14 deletions
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3
ChangeLog.d/psa-ecb-ub.txt Normal file
View File

@ -0,0 +1,3 @@
Bugfix
* Fix undefined behavior (typically harmless in practice) in PSA ECB
encryption and decryption.

37
library/common.h
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@ -25,6 +25,7 @@
#include "mbedtls/build_info.h"
#include <stddef.h>
#include <stdint.h>
/** Helper to define a function as static except when building invasive tests.
@ -68,6 +69,42 @@ extern void (*mbedtls_test_hook_test_fail)( const char * test, int line, const c
*/
#define MBEDTLS_ALLOW_PRIVATE_ACCESS
/** Return an offset into a buffer.
*
* This is just the addition of an offset to a pointer, except that this
* function also accepts an offset of 0 into a buffer whose pointer is null.
*
* \param p Pointer to a buffer of at least n bytes.
* This may be \p NULL if \p n is zero.
* \param n An offset in bytes.
* \return Pointer to offset \p n in the buffer \p p.
* Note that this is only a valid pointer if the size of the
* buffer is at least \p n + 1.
*/
static inline unsigned char *mbedtls_buffer_offset(
unsigned char *p, size_t n )
{
return( p == NULL ? NULL : p + n );
}
/** Return an offset into a read-only buffer.
*
* This is just the addition of an offset to a pointer, except that this
* function also accepts an offset of 0 into a buffer whose pointer is null.
*
* \param p Pointer to a buffer of at least n bytes.
* This may be \p NULL if \p n is zero.
* \param n An offset in bytes.
* \return Pointer to offset \p n in the buffer \p p.
* Note that this is only a valid pointer if the size of the
* buffer is at least \p n + 1.
*/
static inline const unsigned char *mbedtls_buffer_offset_const(
const unsigned char *p, size_t n )
{
return( p == NULL ? NULL : p + n );
}
/** Byte Reading Macros
*
* Given a multi-byte integer \p x, MBEDTLS_BYTE_n retrieves the n-th

4
library/psa_crypto.c
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@ -3454,8 +3454,8 @@ psa_status_t psa_cipher_encrypt( mbedtls_svc_key_id_t key,
status = psa_driver_wrapper_cipher_encrypt(
&attributes, slot->key.data, slot->key.bytes,
alg, local_iv, default_iv_length, input, input_length,
output + default_iv_length, output_size - default_iv_length,
output_length );
mbedtls_buffer_offset( output, default_iv_length ),
output_size - default_iv_length, output_length );
exit:
unlock_status = psa_unlock_key_slot( slot );

23
library/psa_crypto_cipher.c
View File

@ -516,10 +516,10 @@ psa_status_t mbedtls_psa_cipher_encrypt(
if( status != PSA_SUCCESS )
goto exit;
status = mbedtls_psa_cipher_finish( &operation,
output + update_output_length,
output_size - update_output_length,
&finish_output_length );
status = mbedtls_psa_cipher_finish(
&operation,
mbedtls_buffer_offset( output, update_output_length ),
output_size - update_output_length, &finish_output_length );
if( status != PSA_SUCCESS )
goto exit;
@ -563,17 +563,20 @@ psa_status_t mbedtls_psa_cipher_decrypt(
goto exit;
}
status = mbedtls_psa_cipher_update( &operation, input + operation.iv_length,
input_length - operation.iv_length,
output, output_size, &olength );
status = mbedtls_psa_cipher_update(
&operation,
mbedtls_buffer_offset_const( input, operation.iv_length ),
input_length - operation.iv_length,
output, output_size, &olength );
if( status != PSA_SUCCESS )
goto exit;
accumulated_length = olength;
status = mbedtls_psa_cipher_finish( &operation, output + accumulated_length,
output_size - accumulated_length,
&olength );
status = mbedtls_psa_cipher_finish(
&operation,
mbedtls_buffer_offset( output, accumulated_length ),
output_size - accumulated_length, &olength );
if( status != PSA_SUCCESS )
goto exit;

5
tests/suites/test_suite_psa_crypto.function
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@ -4,6 +4,7 @@
#include "mbedtls/asn1.h"
#include "mbedtls/asn1write.h"
#include "mbedtls/oid.h"
#include "common.h"
/* For MBEDTLS_CTR_DRBG_MAX_REQUEST, knowing that psa_generate_random()
* uses mbedtls_ctr_drbg internally. */
@ -3983,7 +3984,7 @@ void cipher_alg_without_iv( int alg_arg, int key_type_arg, data_t *key_data,
TEST_LE_U( length, output_buffer_size );
output_length += length;
PSA_ASSERT( psa_cipher_finish( &operation,
output + output_length,
mbedtls_buffer_offset( output, output_length ),
output_buffer_size - output_length,
&length ) );
output_length += length;
@ -4001,7 +4002,7 @@ void cipher_alg_without_iv( int alg_arg, int key_type_arg, data_t *key_data,
TEST_LE_U( length, output_buffer_size );
output_length += length;
PSA_ASSERT( psa_cipher_finish( &operation,
output + output_length,
mbedtls_buffer_offset( output, output_length ),
output_buffer_size - output_length,
&length ) );
output_length += length;