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Fix NULL+0 in addition 0 + 0

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Fix undefined behavior (typically harmless in practice) of
mbedtls_mpi_add_mpi(), mbedtls_mpi_add_abs() and mbedtls_mpi_add_int() when
both operands are 0 and the left operand is represented with 0 limbs.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2022-11-15 22:59:00 +01:00
parent 6110a16555
commit db14a9d180
2 changed files with 9 additions and 0 deletions
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4
ChangeLog.d/mpi-add-0-ub.txt Normal file
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@ -0,0 +1,4 @@
Bugfix
* Fix undefined behavior (typically harmless in practice) of
mbedtls_mpi_add_mpi(), mbedtls_mpi_add_abs() and mbedtls_mpi_add_int()
when both operands are 0 and the left operand is represented with 0 limbs.

5
library/bignum.c
View file

@ -889,6 +889,11 @@ int mbedtls_mpi_add_abs( mbedtls_mpi *X, const mbedtls_mpi *A, const mbedtls_mpi
if( B->p[j - 1] != 0 ) if( B->p[j - 1] != 0 )
break; 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 ) ); MBEDTLS_MPI_CHK( mbedtls_mpi_grow( X, j ) );
/* j is the number of non-zero limbs of B. Add those to X. */ /* j is the number of non-zero limbs of B. Add those to X. */