[PATCH v2] clk: zynq: Prevent null pointer dereference caused by kmalloc failure

[PATCH v2] clk: zynq: Prevent null pointer dereference caused by kmalloc failure

[Duoming Zhou]

The kmalloc() in zynq_clk_setup() will return null if the
physical memory has run out. As a result, if we use snprintf
to write data to the null address, the null pointer dereference
bug will happen.

This patch adds a stack variable to replace the kmalloc().

Fixes: 0ee52b157b8e ("clk: zynq: Add clock controller driver")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
Changes in v2:
  - Use stack variable to replace kmalloc().

 drivers/clk/zynq/clkc.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/clk/zynq/clkc.c b/drivers/clk/zynq/clkc.c
index 7bdeaff2bfd..e4c4c9adf79 100644
--- a/drivers/clk/zynq/clkc.c
+++ b/drivers/clk/zynq/clkc.c
@@ -427,7 +427,7 @@ static void __init zynq_clk_setup(struct device_node *np)
 			SLCR_GEM1_CLK_CTRL, 0, 0, &gem1clk_lock);
 
 	tmp = strlen("mio_clk_00x");
-	clk_name = kmalloc(tmp, GFP_KERNEL);
+	char clk_name[tmp];
 	for (i = 0; i < NUM_MIO_PINS; i++) {
 		int idx;
 
@@ -439,7 +439,6 @@ static void __init zynq_clk_setup(struct device_node *np)
 		else
 			can_mio_mux_parents[i] = dummy_nm;
 	}
-	kfree(clk_name);
 	clk_register_mux(NULL, "can_mux", periph_parents, 4,
 			CLK_SET_RATE_NO_REPARENT, SLCR_CAN_CLK_CTRL, 4, 2, 0,
 			&canclk_lock);
-- 
2.17.1


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Re: [PATCH v2] clk: zynq: Prevent null pointer dereference caused by kmalloc failure

[Michal Simek]

On 2/29/24 13:22, Duoming Zhou wrote:
> The kmalloc() in zynq_clk_setup() will return null if the
> physical memory has run out. As a result, if we use snprintf
> to write data to the null address, the null pointer dereference
> bug will happen.
> 
> This patch adds a stack variable to replace the kmalloc().
> 
> Fixes: 0ee52b157b8e ("clk: zynq: Add clock controller driver")
> Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
> ---
> Changes in v2:
>    - Use stack variable to replace kmalloc().
> 
>   drivers/clk/zynq/clkc.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/zynq/clkc.c b/drivers/clk/zynq/clkc.c
> index 7bdeaff2bfd..e4c4c9adf79 100644
> --- a/drivers/clk/zynq/clkc.c
> +++ b/drivers/clk/zynq/clkc.c
> @@ -427,7 +427,7 @@ static void __init zynq_clk_setup(struct device_node *np)
>   			SLCR_GEM1_CLK_CTRL, 0, 0, &gem1clk_lock);
>   
>   	tmp = strlen("mio_clk_00x");
> -	clk_name = kmalloc(tmp, GFP_KERNEL);
> +	char clk_name[tmp];

I know that Stephen asked for it but variable with variable length in the middle 
of code doesn't look good or useful.
I would allocate rather bigger array on stack with size bigger than max length 
which will use it.

Thanks,
Michal

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Re: [PATCH v2] clk: zynq: Prevent null pointer dereference caused by kmalloc failure

[duoming]

On Thu, 29 Feb 2024 13:45:54 +0100 Michal Simek wrote:
> > The kmalloc() in zynq_clk_setup() will return null if the
> > physical memory has run out. As a result, if we use snprintf
> > to write data to the null address, the null pointer dereference
> > bug will happen.
> > 
> > This patch adds a stack variable to replace the kmalloc().
> > 
> > Fixes: 0ee52b157b8e ("clk: zynq: Add clock controller driver")
> > Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
> > ---
> > Changes in v2:
> >    - Use stack variable to replace kmalloc().
> > 
> >   drivers/clk/zynq/clkc.c | 3 +--
> >   1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/drivers/clk/zynq/clkc.c b/drivers/clk/zynq/clkc.c
> > index 7bdeaff2bfd..e4c4c9adf79 100644
> > --- a/drivers/clk/zynq/clkc.c
> > +++ b/drivers/clk/zynq/clkc.c
> > @@ -427,7 +427,7 @@ static void __init zynq_clk_setup(struct device_node *np)
> >   			SLCR_GEM1_CLK_CTRL, 0, 0, &gem1clk_lock);
> >   
> >   	tmp = strlen("mio_clk_00x");
> > -	clk_name = kmalloc(tmp, GFP_KERNEL);
> > +	char clk_name[tmp];
> 
> I know that Stephen asked for it but variable with variable length in the middle 
> of code doesn't look good or useful.
> I would allocate rather bigger array on stack with size bigger than max length 
> which will use it.

The length of "mio_clk_00x" is 11 bytes, and the kernel will alloc 16 bytes to it.
I use a local variable whose size is 16 bytes to replace it. The detail is shown
below:

diff --git a/drivers/clk/zynq/clkc.c b/drivers/clk/zynq/clkc.c
index 7bdeaff2bfd..81d530e3357 100644
--- a/drivers/clk/zynq/clkc.c
+++ b/drivers/clk/zynq/clkc.c
@@ -215,7 +215,7 @@ static void __init zynq_clk_setup(struct device_node *np)
        int i;
        u32 tmp;
        int ret;
-       char *clk_name;
+       char clk_name[16];
        unsigned int fclk_enable = 0;
        const char *clk_output_name[clk_max];
        const char *cpu_parents[4];
@@ -427,7 +427,6 @@ static void __init zynq_clk_setup(struct device_node *np)
                        SLCR_GEM1_CLK_CTRL, 0, 0, &gem1clk_lock);

        tmp = strlen("mio_clk_00x");
-       clk_name = kmalloc(tmp, GFP_KERNEL);
        for (i = 0; i < NUM_MIO_PINS; i++) {
                int idx;

@@ -439,7 +438,6 @@ static void __init zynq_clk_setup(struct device_node *np)
                else
                        can_mio_mux_parents[i] = dummy_nm;
        }
-       kfree(clk_name);
        clk_register_mux(NULL, "can_mux", periph_parents, 4,
                        CLK_SET_RATE_NO_REPARENT, SLCR_CAN_CLK_CTRL, 4, 2, 0,
                        &canclk_lock);

Do you think the above is better?

Best regards,
Duoming Zhou
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Re: [PATCH v2] clk: zynq: Prevent null pointer dereference caused by kmalloc failure

[Stephen Boyd]

Quoting Michal Simek (2024-02-29 04:45:54)
> On 2/29/24 13:22, Duoming Zhou wrote:
> > diff --git a/drivers/clk/zynq/clkc.c b/drivers/clk/zynq/clkc.c
> > index 7bdeaff2bfd..e4c4c9adf79 100644
> > --- a/drivers/clk/zynq/clkc.c
> > +++ b/drivers/clk/zynq/clkc.c
> > @@ -427,7 +427,7 @@ static void __init zynq_clk_setup(struct device_node *np)
> >                       SLCR_GEM1_CLK_CTRL, 0, 0, &gem1clk_lock);
> >   
> >       tmp = strlen("mio_clk_00x");
> > -     clk_name = kmalloc(tmp, GFP_KERNEL);
> > +     char clk_name[tmp];
> 
> I know that Stephen asked for it but variable with variable length in the middle 
> of code doesn't look good or useful.

I didn't ask for it to be in the middle of the function :)

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Re: [PATCH v2] clk: zynq: Prevent null pointer dereference caused by kmalloc failure

[Stephen Boyd]

Quoting duoming@zju.edu.cn (2024-02-29 06:16:28)
> On Thu, 29 Feb 2024 13:45:54 +0100 Michal Simek wrote:
> 
> The length of "mio_clk_00x" is 11 bytes, and the kernel will alloc 16 bytes to it.
> I use a local variable whose size is 16 bytes to replace it. The detail is shown
> below:
> 
> diff --git a/drivers/clk/zynq/clkc.c b/drivers/clk/zynq/clkc.c
> index 7bdeaff2bfd..81d530e3357 100644
> --- a/drivers/clk/zynq/clkc.c
> +++ b/drivers/clk/zynq/clkc.c
> @@ -215,7 +215,7 @@ static void __init zynq_clk_setup(struct device_node *np)
>         int i;
>         u32 tmp;
>         int ret;
> -       char *clk_name;
> +       char clk_name[16];
>         unsigned int fclk_enable = 0;
>         const char *clk_output_name[clk_max];
>         const char *cpu_parents[4];
> @@ -427,7 +427,6 @@ static void __init zynq_clk_setup(struct device_node *np)
>                         SLCR_GEM1_CLK_CTRL, 0, 0, &gem1clk_lock);
> 
>         tmp = strlen("mio_clk_00x");

Is tmp used now?

> -       clk_name = kmalloc(tmp, GFP_KERNEL);
>         for (i = 0; i < NUM_MIO_PINS; i++) {
>                 int idx;
> 
> @@ -439,7 +438,6 @@ static void __init zynq_clk_setup(struct device_node *np)
>                 else
>                         can_mio_mux_parents[i] = dummy_nm;
>         }
> -       kfree(clk_name);
>         clk_register_mux(NULL, "can_mux", periph_parents, 4,
>                         CLK_SET_RATE_NO_REPARENT, SLCR_CAN_CLK_CTRL, 4, 2, 0,
>                         &canclk_lock);
> 
> Do you think the above is better?
> 

It's getting there.

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Re: [PATCH v2] clk: zynq: Prevent null pointer dereference caused by kmalloc failure

[Michal Simek]

On 3/1/24 02:21, Stephen Boyd wrote:
> Quoting Michal Simek (2024-02-29 04:45:54)
>> On 2/29/24 13:22, Duoming Zhou wrote:
>>> diff --git a/drivers/clk/zynq/clkc.c b/drivers/clk/zynq/clkc.c
>>> index 7bdeaff2bfd..e4c4c9adf79 100644
>>> --- a/drivers/clk/zynq/clkc.c
>>> +++ b/drivers/clk/zynq/clkc.c
>>> @@ -427,7 +427,7 @@ static void __init zynq_clk_setup(struct device_node *np)
>>>                        SLCR_GEM1_CLK_CTRL, 0, 0, &gem1clk_lock);
>>>    
>>>        tmp = strlen("mio_clk_00x");
>>> -     clk_name = kmalloc(tmp, GFP_KERNEL);
>>> +     char clk_name[tmp];
>>
>> I know that Stephen asked for it but variable with variable length in the middle
>> of code doesn't look good or useful.
> 
> I didn't ask for it to be in the middle of the function :)

I didn't say it. :-)
I know it was about putting it on the stack instead.

M


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