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Merge pull request #6609 from gilles-peskine-arm/mpi_sint-min-ub

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Fix undefined behavior in bignum: NULL+0 and -most-negative-sint
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Gilles Peskine 2022-11-21 19:51:58 +01:00 • committed by GitHub
commit 339406daf9
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GPG key ID: 4AEE18F83AFDEB23
6 changed files with 190 additions and 5 deletions
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26
library/bignum.c
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@ -252,6 +252,17 @@ void mbedtls_mpi_swap( mbedtls_mpi *X, mbedtls_mpi *Y )
memcpy( Y, &T, sizeof( mbedtls_mpi ) );
}
static inline mbedtls_mpi_uint mpi_sint_abs( mbedtls_mpi_sint z )
{
if( z >= 0 )
return( z );
/* Take care to handle the most negative value (-2^(biL-1)) correctly.
* A naive -z would have undefined behavior.
* Write this in a way that makes popular compilers happy (GCC, Clang,
* MSVC). */
return( (mbedtls_mpi_uint) 0 - (mbedtls_mpi_uint) z );
}
/*
* Set value from integer
*/
@ -263,7 +274,7 @@ int mbedtls_mpi_lset( mbedtls_mpi *X, mbedtls_mpi_sint z )
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, 1 ) );
memset( X->p, 0, X->n * ciL );
X->p[0] = ( z < 0 ) ? -z : z;
X->p[0] = mpi_sint_abs( z );
X->s = ( z < 0 ) ? -1 : 1;
cleanup:
@ -853,7 +864,7 @@ int mbedtls_mpi_cmp_int( const mbedtls_mpi *X, mbedtls_mpi_sint z )
mbedtls_mpi_uint p[1];
MPI_VALIDATE_RET( X != NULL );
*p = ( z < 0 ) ? -z : z;
*p = mpi_sint_abs( z );
Y.s = ( z < 0 ) ? -1 : 1;
Y.n = 1;
Y.p = p;
@ -889,6 +900,11 @@ int mbedtls_mpi_add_abs( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
if( B->p[j - 1] != 0 )
break;
/* Exit early to avoid undefined behavior on NULL+0 when X->n == 0
* and B is 0 (of any size). */
if( j == 0 )
return( 0 );
MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, j ) );
/* j is the number of non-zero limbs of B. Add those to X. */
@ -1040,7 +1056,7 @@ int mbedtls_mpi_add_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_sint
MPI_VALIDATE_RET( X != NULL );
MPI_VALIDATE_RET( A != NULL );
p[0] = ( b < 0 ) ? -b : b;
p[0] = mpi_sint_abs( b );
B.s = ( b < 0 ) ? -1 : 1;
B.n = 1;
B.p = p;
@ -1058,7 +1074,7 @@ int mbedtls_mpi_sub_int( mbedtls_mpi *X, const mbedtls_mpi *A, mbedtls_mpi_sint
MPI_VALIDATE_RET( X != NULL );
MPI_VALIDATE_RET( A != NULL );
p[0] = ( b < 0 ) ? -b : b;
p[0] = mpi_sint_abs( b );
B.s = ( b < 0 ) ? -1 : 1;
B.n = 1;
B.p = p;
@ -1396,7 +1412,7 @@ int mbedtls_mpi_div_int( mbedtls_mpi *Q, mbedtls_mpi *R,
mbedtls_mpi_uint p[1];
MPI_VALIDATE_RET( A != NULL );
p[0] = ( b < 0 ) ? -b : b;
p[0] = mpi_sint_abs( b );
B.s = ( b < 0 ) ? -1 : 1;
B.n = 1;
B.p = p;