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To:     Yannick Fertre <yannick.fertre@st.com>,
        Philippe Cornu <philippe.cornu@st.com>,
        Benjamin Gaignard <benjamin.gaignard@st.com>,
        Vincent Abriou <vincent.abriou@st.com>,
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        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        <dri-devel@lists.freedesktop.org>,
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        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
Subject: [PATCH] drm/stm: ltdc: limit number of layer to avoid memory overflow
Date:   Wed, 3 Apr 2019 11:20:16 +0200
Message-ID: <1554283216-2700-1-git-send-email-yannick.fertre@st.com>
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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@st.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