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From:   Brian Gix <brian.gix@intel.com>
To:     linux-bluetooth@vger.kernel.org
Cc:     inga.stotland@intel.com, brian.gix@intel.com,
        jakub.witowski@silvair.com, michal.lowas-rzechonek@silvair.com
Subject: [PATCH BlueZ] mesh: Fix long MIC usage in segmented messages
Date:   Thu, 23 May 2019 10:53:21 -0700
Message-Id: <20190523175321.13094-1-brian.gix@intel.com>
Sender: linux-bluetooth-owner@vger.kernel.org
Precedence: bulk

From: Jakub Witowski <jakub.witowski@silvair.com>

Contrary to the comment, implementation used a 8-byte MIC even if this
generated an additional segment.
---
 mesh/model.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mesh/model.c b/mesh/model.c
index 034d54496..90bb62db8 100644
--- a/mesh/model.c
+++ b/mesh/model.c
@@ -40,6 +40,9 @@
 #include "mesh/util.h"
 #include "mesh/model.h"
 
+/* Divide and round to ceiling (up) to calculate segment count */
+#define CEILDIV(val, div) (((val) + (div) - 1) / (div))
+
 struct mesh_model {
 	const struct mesh_model_ops *cbs;
 	void *user_data;
@@ -451,7 +454,7 @@ static bool msg_send(struct mesh_node *node, bool credential, uint16_t src,
 
 	/* Use large MIC if it doesn't affect segmentation */
 	if (msg_len > 11 && msg_len <= 376) {
-		if ((out_len / 12) == ((out_len + 4) / 12)) {
+		if (CEILDIV(out_len, 12) == CEILDIV(out_len + 4, 12)) {
 			szmic = true;
 			out_len = msg_len + sizeof(uint64_t);
 		}
-- 
2.14.5