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Fix undefined behavior with the most negative mbedtls_mpi_sint

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When x is the most negative value of a two's complement type,
`(unsigned_type)(-x)` has undefined behavior, whereas `-(unsigned_type)x`
has well-defined behavior and does what was intended.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2022-11-15 23:02:14 +01:00
parent db14a9d180
commit af601f9751
4 changed files with 156 additions and 5 deletions
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10
library/bignum.c
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@ -263,7 +263,7 @@ 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] = ( z < 0 ) ? -(mbedtls_mpi_uint)z : z;
X->s = ( z < 0 ) ? -1 : 1;
cleanup:
@ -853,7 +853,7 @@ 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 = ( z < 0 ) ? -(mbedtls_mpi_uint)z : z;
Y.s = ( z < 0 ) ? -1 : 1;
Y.n = 1;
Y.p = p;
@ -1057,7 +1057,7 @@ 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] = ( b < 0 ) ? -(mbedtls_mpi_uint)b : b;
B.s = ( b < 0 ) ? -1 : 1;
B.n = 1;
B.p = p;
@ -1075,7 +1075,7 @@ 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] = ( b < 0 ) ? -(mbedtls_mpi_uint)b : b;
B.s = ( b < 0 ) ? -1 : 1;
B.n = 1;
B.p = p;
@ -1413,7 +1413,7 @@ 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] = ( b < 0 ) ? -(mbedtls_mpi_uint)b : b;
B.s = ( b < 0 ) ? -1 : 1;
B.n = 1;
B.p = p;