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

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Date:   Tue, 28 Jan 2020 09:43:02 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Rob Herring <robh@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Jeffrey Hugo <jhugo@...eaurora.org>,
        Taniya Das <tdas@...eaurora.org>, devicetree@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, harigovi@...eaurora.org,
        kalyan_t@...eaurora.org, Mark Rutland <mark.rutland@....com>,
        linux-clk@...r.kernel.org, hoegsberg@...omium.org,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 01/10] clk: qcom: rcg2: Don't crash if our parent
 can't be found; return an error

On Fri, Jan 24, 2020 at 02:42:16PM -0800, Douglas Anderson wrote:
> 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) {

Reviewed-by: Matthias Kaehlcke <mka@...omium.org>