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mbedtls: fix hw accelerated big-num mul if operand and result overlap

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this issue is mainly exposed when using larger (4096) client key in TLS mutual auth,
since it uses multiplications > 2048 when mbedtls_mpi_mul_mpi is used in recursion,
which works only if both operands point to different location than result since
mpi_mult_mpi_overlong() called mbedtls_mpi_grow() to reallocate buffers used in previous
pointer arithmetics and thus corrupting it. Fixed by growing the mpi buffer before
calling mpi_mult_mpi_overlong()
This commit is contained in:
David Cermak 2020-01-04 17:18:46 +01:00
parent bdf477e76d
commit 7b495db118
1 changed files with 3 additions and 5 deletions
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8
components/mbedtls/port/esp_bignum.c
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@ -508,6 +508,9 @@ int mbedtls_mpi_mul_mpi( mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi
return ret;
}
/* Grow Z to result size early, avoid interim allocations */
MBEDTLS_MPI_CHK( mbedtls_mpi_grow(Z, z_words) );
/* If either factor is over 2048 bits, we can't use the standard hardware multiplier
(it assumes result is double longest factor, and result is max 4096 bits.)
@ -552,8 +555,6 @@ int mbedtls_mpi_mul_mpi( mbedtls_mpi *Z, const mbedtls_mpi *X, const mbedtls_mpi
start_op(RSA_MULT_START_REG);
MBEDTLS_MPI_CHK( mbedtls_mpi_grow(Z, z_words) );
wait_op_complete(RSA_MULT_START_REG);
/* Read back the result */
@ -660,9 +661,6 @@ static int mpi_mult_mpi_overlong(mbedtls_mpi *Z, const mbedtls_mpi *X, const mbe
};
mbedtls_mpi_init(&Ztemp);
/* Grow Z to result size early, avoid interim allocations */
mbedtls_mpi_grow(Z, z_words);
/* Get result Ztemp = Yp * X (need temporary variable Ztemp) */
MBEDTLS_MPI_CHK( mbedtls_mpi_mul_mpi(&Ztemp, X, &Yp) );