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DHM: Fix dhm_check_range() always returning 0

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Although the variable ret was initialised to an error, the
MBEDTLS_MPI_CHK macro was overwriting it. Therefore it ended up being
0 whenewer the bignum computation was successfull and stayed 0
independently of the actual check.
This commit is contained in:
Janos Follath 2017-09-20 15:33:24 +01:00
parent 4b151fabb7
commit aa325d7b7f
2 changed files with 12 additions and 5 deletions
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6
ChangeLog
View file

@ -1,6 +1,10 @@
mbed TLS ChangeLog (Sorted per branch, date)
= mbed TLS x.x.x released xxxx-xx-xx
= mbed TLS x.x.x branch released xxxx-xx-xx
Security
* Fix dhm_check_range() failing to detect trivial subgroups and essentially
always returning 0. Reported by prashantkspatil.
Bugfix
* Fix ssl_parse_record_header() to silently discard invalid DTLS records

11
library/dhm.c
View file

@ -93,6 +93,9 @@ static int dhm_read_bignum( mbedtls_mpi *X,
*
* Parameter should be: 2 <= public_param <= P - 2
*
* This means that we need to return an error if
* public_param < 2 or public param > P-2
*
* For more information on the attack, see:
* http://www.cl.cam.ac.uk/~rja14/Papers/psandqs.pdf
* http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2005-2643
@ -100,17 +103,17 @@ static int dhm_read_bignum( mbedtls_mpi *X,
static int dhm_check_range( const mbedtls_mpi *param, const mbedtls_mpi *P )
{
mbedtls_mpi L, U;
int ret = MBEDTLS_ERR_DHM_BAD_INPUT_DATA;
int ret = 0;
mbedtls_mpi_init( &L ); mbedtls_mpi_init( &U );
MBEDTLS_MPI_CHK( mbedtls_mpi_lset( &L, 2 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_int( &U, P, 2 ) );
if( mbedtls_mpi_cmp_mpi( param, &L ) >= 0 &&
mbedtls_mpi_cmp_mpi( param, &U ) <= 0 )
if( mbedtls_mpi_cmp_mpi( param, &L ) < 0 ||
mbedtls_mpi_cmp_mpi( param, &U ) > 0 )
{
ret = 0;
ret = MBEDTLS_ERR_DHM_BAD_INPUT_DATA;
}
cleanup: