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ECP: Prevent freeing a buffer on stack

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The function ecp_mod_koblitz computed the space for the result of a
multiplication optimally for that specific case, but unfortunately
the function mbedtls_mpi_mul_mpi performs a generic, suboptimal
calculation and needs one more limb for the result. Since the result's
buffer is on the stack, the best case scenario is that the program
stops.

This only happened on 64 bit platforms.

Fixes #569
This commit is contained in:
Janos Follath 2017-01-27 16:05:20 +00:00 committed by Simon Butcher
parent 28fff14113
commit 7dadc2f259
2 changed files with 11 additions and 3 deletions
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8
ChangeLog
View file

@ -12,6 +12,14 @@ Security
CertificateVerify messages, to prevent SLOTH attacks against TLS 1.2.
Introduced by interoperability fix for #513.
Security
* Fixed a bug that caused freeing a buffer that was allocated on the stack,
when verifying the validity of a key on secp224k1. This could be
triggered remotely for example with a maliciously constructed certificate
and might have led to remote code execution on some exotic embedded
platforms. Reported independently by rongsaws and Regina Wilson.
CVE-2017-2784
Bugfix
* Fix output certificate verification flags set by x509_crt_verify_top() when
traversing a chain of trusted CA. The issue would cause both flags,

6
library/ecp_curves.c
View file

@ -1213,7 +1213,7 @@ static inline int ecp_mod_koblitz( mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t
int ret;
size_t i;
mbedtls_mpi M, R;
mbedtls_mpi_uint Mp[P_KOBLITZ_MAX + P_KOBLITZ_R];
mbedtls_mpi_uint Mp[P_KOBLITZ_MAX + P_KOBLITZ_R + 1];
if( N->n < p_limbs )
return( 0 );
@ -1235,7 +1235,7 @@ static inline int ecp_mod_koblitz( mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t
memcpy( Mp, N->p + p_limbs - adjust, M.n * sizeof( mbedtls_mpi_uint ) );
if( shift != 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &M, shift ) );
M.n += R.n - adjust; /* Make room for multiplication by R */
M.n += R.n; /* Make room for multiplication by R */
/* N = A0 */
if( mask != 0 )
@ -1257,7 +1257,7 @@ static inline int ecp_mod_koblitz( mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t
memcpy( Mp, N->p + p_limbs - adjust, M.n * sizeof( mbedtls_mpi_uint ) );
if( shift != 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &M, shift ) );
M.n += R.n - adjust; /* Make room for multiplication by R */
M.n += R.n; /* Make room for multiplication by R */
/* N = A0 */
if( mask != 0 )