linux-kernel - [PATCH v2 01/10] clk: qcom: rcg2: Don't crash if our parent can't be found; return an error

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Message-Id: <20200124144154.v2.1.I7487325fe8e701a68a07d3be8a6a4b571eca9cfa@changeid>
Date:   Fri, 24 Jan 2020 14:42:16 -0800
From:   Douglas Anderson <dianders@...omium.org>
To:     Rob Herring <robh@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>
Cc:     Jeffrey Hugo <jhugo@...eaurora.org>,
        Taniya Das <tdas@...eaurora.org>, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, harigovi@...eaurora.org,
        mka@...omium.org, kalyan_t@...eaurora.org,
        Mark Rutland <mark.rutland@....com>, linux-clk@...r.kernel.org,
        hoegsberg@...omium.org, Douglas Anderson <dianders@...omium.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 01/10] clk: qcom: rcg2: Don't crash if our parent can't be found; return an error

When I got my clock parenting slightly wrong I ended up with a crash
that looked like this:

  Unable to handle kernel NULL pointer dereference at virtual
  address 0000000000000000
  ...
  pc : clk_hw_get_rate+0x14/0x44
  ...
  Call trace:
   clk_hw_get_rate+0x14/0x44
   _freq_tbl_determine_rate+0x94/0xfc
   clk_rcg2_determine_rate+0x2c/0x38
   clk_core_determine_round_nolock+0x4c/0x88
   clk_core_round_rate_nolock+0x6c/0xa8
   clk_core_round_rate_nolock+0x9c/0xa8
   clk_core_set_rate_nolock+0x70/0x180
   clk_set_rate+0x3c/0x6c
   of_clk_set_defaults+0x254/0x360
   platform_drv_probe+0x28/0xb0
   really_probe+0x120/0x2dc
   driver_probe_device+0x64/0xfc
   device_driver_attach+0x4c/0x6c
   __driver_attach+0xac/0xc0
   bus_for_each_dev+0x84/0xcc
   driver_attach+0x2c/0x38
   bus_add_driver+0xfc/0x1d0
   driver_register+0x64/0xf8
   __platform_driver_register+0x4c/0x58
   msm_drm_register+0x5c/0x60
   ...

It turned out that clk_hw_get_parent_by_index() was returning NULL and
we weren't checking.  Let's check it so that we don't crash.

Fixes: ac269395cdd8 ("clk: qcom: Convert to clk_hw based provider APIs")
Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
I haven't gone back and tried to reproduce this same crash on older
kernels, but I'll put the blame on commit ac269395cdd8 ("clk: qcom:
Convert to clk_hw based provider APIs").  Before that if we got a NULL
parent back it was fine and dandy since a NULL "struct clk" is valid
to use but a NULL "struct clk_hw" is not.

Changes in v2:
- Patch ("clk: qcom: rcg2: Don't crash...") new for v2.

 drivers/clk/qcom/clk-rcg2.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
index da045b200def..9098001ac805 100644
--- a/drivers/clk/qcom/clk-rcg2.c
+++ b/drivers/clk/qcom/clk-rcg2.c
@@ -218,6 +218,9 @@ static int _freq_tbl_determine_rate(struct clk_hw *hw, const struct freq_tbl *f,

 	clk_flags = clk_hw_get_flags(hw);
 	p = clk_hw_get_parent_by_index(hw, index);
+	if (!p)
+		return -EINVAL;
+
 	if (clk_flags & CLK_SET_RATE_PARENT) {
 		rate = f->freq;
 		if (f->pre_div) {
-- 
2.25.0.341.g760bfbb309-goog