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Revert "Shut up a clang-analyzer warning"

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This reverts commit 2cc69fffcf.

A check was added in mpi_montmul because clang-analyzer warned about a
possibly null pointer. However this was a false positive. Recent
versions of clang-analyzer no longer emit a warning (3.6 does, 6
doesn't).

Incidentally, the size check was wrong: mpi_montmul needs
T->n >= 2 * (N->n + 1), not just T->n >= N->n + 1.

Given that this is an internal function which is only used from one
public function and in a tightly controlled way, remove both the null
check (which is of low value to begin with) and the size check (which
would be slightly more valuable, but was wrong anyway). This allows
the function not to need to return an error, which makes the source
code a little easier to read and makes the object code a little
smaller.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2020-06-04 20:55:15 +02:00
parent 742f1a4528
commit 4e91d473c3
1 changed files with 14 additions and 19 deletions
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33
library/bignum.c
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@ -1980,15 +1980,12 @@ static void mpi_montg_init( mbedtls_mpi_uint *mm, const mbedtls_mpi *N )
/* /*
* Montgomery multiplication: A = A * B * R^-1 mod N (HAC 14.36) * Montgomery multiplication: A = A * B * R^-1 mod N (HAC 14.36)
*/ */
static int mpi_montmul( mbedtls_mpi *A, const mbedtls_mpi *B, const mbedtls_mpi *N, mbedtls_mpi_uint mm, static void mpi_montmul( mbedtls_mpi *A, const mbedtls_mpi *B, const mbedtls_mpi *N, mbedtls_mpi_uint mm,
const mbedtls_mpi *T ) const mbedtls_mpi *T )
{ {
size_t i, n, m; size_t i, n, m;
mbedtls_mpi_uint u0, u1, *d; mbedtls_mpi_uint u0, u1, *d;
if( T->n < N->n + 1 || T->p == NULL )
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
memset( T->p, 0, T->n * ciL ); memset( T->p, 0, T->n * ciL );
d = T->p; d = T->p;
@ -2016,15 +2013,13 @@ static int mpi_montmul( mbedtls_mpi *A, const mbedtls_mpi *B, const mbedtls_mpi
else else
/* prevent timing attacks */ /* prevent timing attacks */
mpi_sub_hlp( n, A->p, T->p ); mpi_sub_hlp( n, A->p, T->p );
return( 0 );
} }
/* /*
* Montgomery reduction: A = A * R^-1 mod N * Montgomery reduction: A = A * R^-1 mod N
*/ */
static int mpi_montred( mbedtls_mpi *A, const mbedtls_mpi *N, static void mpi_montred( mbedtls_mpi *A, const mbedtls_mpi *N,
mbedtls_mpi_uint mm, const mbedtls_mpi *T ) mbedtls_mpi_uint mm, const mbedtls_mpi *T )
{ {
mbedtls_mpi_uint z = 1; mbedtls_mpi_uint z = 1;
mbedtls_mpi U; mbedtls_mpi U;
@ -2032,7 +2027,7 @@ static int mpi_montred( mbedtls_mpi *A, const mbedtls_mpi *N,
U.n = U.s = (int) z; U.n = U.s = (int) z;
U.p = &z; U.p = &z;
return( mpi_montmul( A, &U, N, mm, T ) ); mpi_montmul( A, &U, N, mm, T );
} }
/* /*
@ -2118,13 +2113,13 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
else else
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[1], A ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[1], A ) );
MBEDTLS_MPI_CHK( mpi_montmul( &W[1], &RR, N, mm, &T ) ); mpi_montmul( &W[1], &RR, N, mm, &T );
/* /*
* X = R^2 * R^-1 mod N = R mod N * X = R^2 * R^-1 mod N = R mod N
*/ */
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( X, &RR ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( X, &RR ) );
MBEDTLS_MPI_CHK( mpi_montred( X, N, mm, &T ) ); mpi_montred( X, N, mm, &T );
if( wsize > 1 ) if( wsize > 1 )
{ {
@ -2137,7 +2132,7 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[j], &W[1] ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[j], &W[1] ) );
for( i = 0; i < wsize - 1; i++ ) for( i = 0; i < wsize - 1; i++ )
MBEDTLS_MPI_CHK( mpi_montmul( &W[j], &W[j], N, mm, &T ) ); mpi_montmul( &W[j], &W[j], N, mm, &T );
/* /*
* W[i] = W[i - 1] * W[1] * W[i] = W[i - 1] * W[1]
@ -2147,7 +2142,7 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[i], N->n + 1 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_grow( &W[i], N->n + 1 ) );
MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[i], &W[i - 1] ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_copy( &W[i], &W[i - 1] ) );
MBEDTLS_MPI_CHK( mpi_montmul( &W[i], &W[1], N, mm, &T ) ); mpi_montmul( &W[i], &W[1], N, mm, &T );
} }
} }
@ -2184,7 +2179,7 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
/* /*
* out of window, square X * out of window, square X
*/ */
MBEDTLS_MPI_CHK( mpi_montmul( X, X, N, mm, &T ) ); mpi_montmul( X, X, N, mm, &T );
continue; continue;
} }
@ -2202,12 +2197,12 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
* X = X^wsize R^-1 mod N * X = X^wsize R^-1 mod N
*/ */
for( i = 0; i < wsize; i++ ) for( i = 0; i < wsize; i++ )
MBEDTLS_MPI_CHK( mpi_montmul( X, X, N, mm, &T ) ); mpi_montmul( X, X, N, mm, &T );
/* /*
* X = X * W[wbits] R^-1 mod N * X = X * W[wbits] R^-1 mod N
*/ */
MBEDTLS_MPI_CHK( mpi_montmul( X, &W[wbits], N, mm, &T ) ); mpi_montmul( X, &W[wbits], N, mm, &T );
state--; state--;
nbits = 0; nbits = 0;
@ -2220,18 +2215,18 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
*/ */
for( i = 0; i < nbits; i++ ) for( i = 0; i < nbits; i++ )
{ {
MBEDTLS_MPI_CHK( mpi_montmul( X, X, N, mm, &T ) ); mpi_montmul( X, X, N, mm, &T );
wbits <<= 1; wbits <<= 1;
if( ( wbits & ( one << wsize ) ) != 0 ) if( ( wbits & ( one << wsize ) ) != 0 )
MBEDTLS_MPI_CHK( mpi_montmul( X, &W[1], N, mm, &T ) ); mpi_montmul( X, &W[1], N, mm, &T );
} }
/* /*
* X = A^E * R * R^-1 mod N = A^E mod N * X = A^E * R * R^-1 mod N = A^E mod N
*/ */
MBEDTLS_MPI_CHK( mpi_montred( X, N, mm, &T ) ); mpi_montred( X, N, mm, &T );
if( neg && E->n != 0 && ( E->p[0] & 1 ) != 0 ) if( neg && E->n != 0 && ( E->p[0] & 1 ) != 0 )
{ {