From b10c66073f3f83359d8333768f9fed2733c11c87 Mon Sep 17 00:00:00 2001 From: Hanno Becker Date: Fri, 26 Oct 2018 13:50:13 +0100 Subject: [PATCH] Detect unsigned integer overflow in mbedtls_ecp_check_budget() This commit modifies a bounds check in `mbedtls_ecp_check_budget()` to be correct even if the requested number of ECC operations would overflow the operation counter. --- library/ecp.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/library/ecp.c b/library/ecp.c index b193ad4f8..de5725c70 100644 --- a/library/ecp.c +++ b/library/ecp.c @@ -248,9 +248,16 @@ int mbedtls_ecp_check_budget( const mbedtls_ecp_group *grp, else if( grp->pbits >= 384 ) ops *= 2; - /* avoid infinite loops: always allow first step */ - if( rs_ctx->ops_done != 0 && rs_ctx->ops_done + ops > ecp_max_ops ) + /* Avoid infinite loops: always allow first step. + * Because of that, however, it's not generally true + * that ops_done <= ecp_max_ops, so the check + * ops_done > ecp_max_ops below is mandatory. */ + if( ( rs_ctx->ops_done != 0 ) && + ( rs_ctx->ops_done > ecp_max_ops || + ops > ecp_max_ops - rs_ctx->ops_done ) ) + { return( MBEDTLS_ERR_ECP_IN_PROGRESS ); + } /* update running count */ rs_ctx->ops_done += ops;