[PATCH v4 01/15] clk: qcom: rcg2: Don't crash if our parent can't be found; return an error

From: Douglas Anderson <dianders@chromium.org>
To: Rob Herring <robh@kernel.org>, Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Stephen Boyd <sboyd@kernel.org>
Cc: Jeffrey Hugo <jhugo@codeaurora.org>,
	Taniya Das <tdas@codeaurora.org>,
	jeffrey.l.hugo@gmail.com, linux-arm-msm@vger.kernel.org,
	harigovi@codeaurora.org, devicetree@vger.kernel.org,
	mka@chromium.org, kalyan_t@codeaurora.org,
	Mark Rutland <mark.rutland@arm.com>,
	linux-clk@vger.kernel.org, hoegsberg@chromium.org,
	Douglas Anderson <dianders@chromium.org>,
	Michael Turquette <mturquette@baylibre.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH v4 01/15] clk: qcom: rcg2: Don't crash if our parent can't be found; return an error
Date: Mon,  3 Feb 2020 10:31:34 -0800
Message-ID: <20200203103049.v4.1.I7487325fe8e701a68a07d3be8a6a4b571eca9cfa@changeid> (raw)
In-Reply-To: <20200203183149.73842-1-dianders@chromium.org>

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@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.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 v4: None
Changes in v3:
- Add Matthias tag.

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

