[PATCH v2] lkdtm/bugs: Check for the NULL pointer after calling kmalloc

[PATCH v2] lkdtm/bugs: Check for the NULL pointer after calling kmalloc

[Jiasheng Jiang]

As the possible failure of the kmalloc(), the not_checked and checked
could be NULL pointer.
Therefore, it should be better to check it in order to avoid the
dereference of the NULL pointer.
Also, we need to kfree the 'not_checked' and 'checked' to avoid
the memory leak if fails.
And since it is just a test, it may directly return without error
number.

Fixes: ae2e1aad3e48 ("drivers/misc/lkdtm/bugs.c: add arithmetic overflow and array bounds checks")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
---
Changelog

v1 -> v2

* Change 1. Add the kfree if fails.
---
 drivers/misc/lkdtm/bugs.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
index f4cb94a9aa9c..c35ea54824ac 100644
--- a/drivers/misc/lkdtm/bugs.c
+++ b/drivers/misc/lkdtm/bugs.c
@@ -325,6 +325,11 @@ void lkdtm_ARRAY_BOUNDS(void)
 
 	not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL);
 	checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL);
+	if (!not_checked || !checked) {
+		kfree(not_checked);
+		kfree(checked);
+		return;
+	}
 
 	pr_info("Array access within bounds ...\n");
 	/* For both, touch all bytes in the actual member size. */
-- 
2.25.1

Re: [PATCH v2] lkdtm/bugs: Check for the NULL pointer after calling kmalloc

[Kees Cook]

On Wed, Jan 19, 2022 at 08:20:55PM +0800, Jiasheng Jiang wrote:
> As the possible failure of the kmalloc(), the not_checked and checked
> could be NULL pointer.
> Therefore, it should be better to check it in order to avoid the
> dereference of the NULL pointer.
> Also, we need to kfree the 'not_checked' and 'checked' to avoid
> the memory leak if fails.
> And since it is just a test, it may directly return without error
> number.
> 
> Fixes: ae2e1aad3e48 ("drivers/misc/lkdtm/bugs.c: add arithmetic overflow and array bounds checks")
> Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
> ---
> Changelog
> 
> v1 -> v2
> 
> * Change 1. Add the kfree if fails.
> ---
>  drivers/misc/lkdtm/bugs.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
> index f4cb94a9aa9c..c35ea54824ac 100644
> --- a/drivers/misc/lkdtm/bugs.c
> +++ b/drivers/misc/lkdtm/bugs.c
> @@ -325,6 +325,11 @@ void lkdtm_ARRAY_BOUNDS(void)
>  
>  	not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL);
>  	checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL);
> +	if (!not_checked || !checked) {
> +		kfree(not_checked);
> +		kfree(checked);
> +		return;
> +	}

This should explicitly yell about the memory failure. See the other
error cases for examples. I'd expect something like this before the
return:

		pr_err("FAIL: could not allocate required buffers\n");

-Kees

>  
>  	pr_info("Array access within bounds ...\n");
>  	/* For both, touch all bytes in the actual member size. */
> -- 
> 2.25.1
> 

-- 
Kees Cook

Re: [PATCH v2] lkdtm/bugs: Check for the NULL pointer after calling kmalloc

[Dan Carpenter]

On Wed, Jan 19, 2022 at 10:45:33AM -0800, Kees Cook wrote:
> > diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c
> > index f4cb94a9aa9c..c35ea54824ac 100644
> > --- a/drivers/misc/lkdtm/bugs.c
> > +++ b/drivers/misc/lkdtm/bugs.c
> > @@ -325,6 +325,11 @@ void lkdtm_ARRAY_BOUNDS(void)
> >  
> >  	not_checked = kmalloc(sizeof(*not_checked) * 2, GFP_KERNEL);
> >  	checked = kmalloc(sizeof(*checked) * 2, GFP_KERNEL);
> > +	if (!not_checked || !checked) {
> > +		kfree(not_checked);
> > +		kfree(checked);
> > +		return;
> > +	}
> 
> This should explicitly yell about the memory failure. See the other
> error cases for examples. I'd expect something like this before the
> return:
> 
> 		pr_err("FAIL: could not allocate required buffers\n");

Adding error messages for kmalloc failures is a checkpatch violation.

Those allocations will never fail.  There is already a warning message
and stack trace built into kmalloc().  It's just a waste of resources to
add the warning message.

regards,
dan carpenter