linux-kernel - [PATCH] drm/stm: ltdc: limit number of layer to avoid memory overflow

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Date:   Wed, 3 Apr 2019 11:20:16 +0200
From:   Yannick Fertré <yannick.fertre@...com>
To:     Yannick Fertre <yannick.fertre@...com>,
        Philippe Cornu <philippe.cornu@...com>,
        Benjamin Gaignard <benjamin.gaignard@...com>,
        Vincent Abriou <vincent.abriou@...com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] drm/stm: ltdc: limit number of layer to avoid memory overflow

If the number of layer is greater than LTDC_MAX_LAYER, we can have
memory overflow when reading plane_fpsi[].

Signed-off-by: Yannick Fertré <yannick.fertre@...com>
---
 drivers/gpu/drm/stm/ltdc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
index 32fd6a3..05bd4b6 100644
--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c
@@ -1021,10 +1021,13 @@ static int ltdc_get_caps(struct drm_device *ddev)
 	struct ltdc_device *ldev = ddev->dev_private;
 	u32 bus_width_log2, lcr, gc2r;
 
-	/* at least 1 layer must be managed */
+	/*
+	 * at least 1 layer must be managed & the number of layers
+	 * must not exceed LTDC_MAX_LAYER
+	 */
 	lcr = reg_read(ldev->regs, LTDC_LCR);
 
-	ldev->caps.nb_layers = max_t(int, lcr, 1);
+	ldev->caps.nb_layers = clamp((int)lcr, 1, LTDC_MAX_LAYER);
 
 	/* set data bus width */
 	gc2r = reg_read(ldev->regs, LTDC_GC2R);
-- 
2.7.4