Prevent mpi_mod_write from corrupting the input
Allocate a working buffer to store the converted value needed for the
mpi_mod_write function.
Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/bignum_mod.c b/library/bignum_mod.c
index e986865..916d34a 100644
--- a/library/bignum_mod.c
+++ b/library/bignum_mod.c
@@ -383,38 +383,46 @@
size_t buflen,
mbedtls_mpi_mod_ext_rep ext_rep)
{
- int ret = MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
-
/* Do our best to check if r and m have been set up */
if (r->limbs == 0 || N->limbs == 0) {
- goto cleanup;
+ return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
}
if (r->limbs != N->limbs) {
- goto cleanup;
+ return MBEDTLS_ERR_MPI_BAD_INPUT_DATA;
}
+ int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
+ mbedtls_mpi_uint *working_memory = r->p;
+ size_t working_memory_len = sizeof(mbedtls_mpi_uint) * r->limbs;
+
if (N->int_rep == MBEDTLS_MPI_MOD_REP_MONTGOMERY) {
- ret = mbedtls_mpi_mod_raw_from_mont_rep(r->p, N);
+
+ working_memory = mbedtls_calloc(r->limbs, sizeof(mbedtls_mpi_uint));
+
+ if (working_memory == NULL) {
+ ret = MBEDTLS_ERR_MPI_ALLOC_FAILED;
+ goto cleanup;
+ }
+
+ memcpy(working_memory, r->p, working_memory_len);
+
+ ret = mbedtls_mpi_mod_raw_from_mont_rep(working_memory, N);
if (ret != 0) {
goto cleanup;
}
}
- ret = mbedtls_mpi_mod_raw_write(r->p, N, buf, buflen, ext_rep);
-
- if (N->int_rep == MBEDTLS_MPI_MOD_REP_MONTGOMERY) {
- /* If this fails, the value of r is corrupted and we want to return
- * this error (as opposed to the error code from the write above) to
- * let the caller know. If it succeeds, we want to return the error
- * code from write above. */
- int conv_ret = mbedtls_mpi_mod_raw_to_mont_rep(r->p, N);
- if (ret == 0) {
- ret = conv_ret;
- }
- }
+ ret = mbedtls_mpi_mod_raw_write(working_memory, N, buf, buflen, ext_rep);
cleanup:
+ if (N->int_rep == MBEDTLS_MPI_MOD_REP_MONTGOMERY &&
+ working_memory != NULL) {
+
+ mbedtls_platform_zeroize(working_memory, working_memory_len);
+ mbedtls_free(working_memory);
+ }
+
return ret;
}
/* END MERGE SLOT 7 */