linux-kernel - [PATCH] drm: sun4i: Fix NULL/invalid pointer dereference in sun8i_tcon_top

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Date:   Sat,  6 Apr 2019 01:30:48 +0200
From:   megous@...ous.com
To:     linux-sunxi@...glegroups.com
Cc:     Ondrej Jirman <megous@...ous.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Chen-Yu Tsai <wens@...e.org>,
        dri-devel@...ts.freedesktop.org (open list:DRM DRIVERS FOR ALLWINNER
        A10),
        linux-arm-kernel@...ts.infradead.org (moderated list:ARM/Allwinner
        sunXi SoC support), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] drm: sun4i: Fix NULL/invalid pointer dereference in sun8i_tcon_top_un/bind

From: Ondrej Jirman <megous@...ous.com>

There are two problems here:

1. Not all clk_data->hws[] need to be initialized, depending on various
   configured quirks. This leads to NULL ptr deref in
   clk_hw_unregister_gate() in sun8i_tcon_top_unbind()
2. If there is error when registering the clk_data->hws[],
   err_unregister_gates error path will try to unregister
   IS_ERR()=true (invalid) pointer.

For problem (1) I have this stack trace:

Unable to handle kernel NULL pointer dereference at virtual
  address 0000000000000008
Call trace:
 clk_hw_unregister+0x8/0x18
 clk_hw_unregister_gate+0x14/0x28
 sun8i_tcon_top_unbind+0x2c/0x60
 component_unbind.isra.4+0x2c/0x50
 component_bind_all+0x1d4/0x230
 sun4i_drv_bind+0xc4/0x1a0
 try_to_bring_up_master+0x164/0x1c0
 __component_add+0xa0/0x168
 component_add+0x10/0x18
 sun8i_dw_hdmi_probe+0x18/0x20
 platform_drv_probe+0x3c/0x70
 really_probe+0xcc/0x278
 driver_probe_device+0x34/0xa8

Problem (2) was identified by head scratching.

Signed-off-by: Ondrej Jirman <megous@...ous.com>
---
 drivers/gpu/drm/sun4i/sun8i_tcon_top.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun8i_tcon_top.c b/drivers/gpu/drm/sun4i/sun8i_tcon_top.c
index fc36e0c10a37..b1e7c76e9c17 100644
--- a/drivers/gpu/drm/sun4i/sun8i_tcon_top.c
+++ b/drivers/gpu/drm/sun4i/sun8i_tcon_top.c
@@ -227,7 +227,7 @@ static int sun8i_tcon_top_bind(struct device *dev, struct device *master,
 
 err_unregister_gates:
 	for (i = 0; i < CLK_NUM; i++)
-		if (clk_data->hws[i])
+		if (!IS_ERR_OR_NULL(clk_data->hws[i]))
 			clk_hw_unregister_gate(clk_data->hws[i]);
 	clk_disable_unprepare(tcon_top->bus);
 err_assert_reset:
@@ -245,7 +245,8 @@ static void sun8i_tcon_top_unbind(struct device *dev, struct device *master,
 
 	of_clk_del_provider(dev->of_node);
 	for (i = 0; i < CLK_NUM; i++)
-		clk_hw_unregister_gate(clk_data->hws[i]);
+		if (clk_data->hws[i])
+			clk_hw_unregister_gate(clk_data->hws[i]);
 
 	clk_disable_unprepare(tcon_top->bus);
 	reset_control_assert(tcon_top->rst);
-- 
2.21.0