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Date: Mon, 29 Apr 2024 10:38:03 -0700
From: Kees Cook <keescook@chromium.org>
To: Erick Archer <erick.archer@outlook.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-hardening@vger.kernel.org
Subject: Re: [PATCH] Input: ff-core - prefer struct_size over open coded
 arithmetic
Message-ID: <202404291037.1A42B7C6B@keescook>
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On Sat, Apr 27, 2024 at 05:05:56PM +0200, Erick Archer wrote:
> This is an effort to get rid of all multiplications from allocation
> functions in order to prevent integer overflows [1][2].
> 
> As the "ff" variable is a pointer to "struct ff_device" and this
> structure ends in a flexible array:
> 
> struct ff_device {
> 	[...]
> 	struct file *effect_owners[] __counted_by(max_effects);
> };
> 
> the preferred way in the kernel is to use the struct_size() helper to
> do the arithmetic instead of the calculation "size + count * size" in
> the kzalloc() function.
> 
> The struct_size() helper returns SIZE_MAX on overflow. So, refactor
> the comparison to take advantage of this.
> 
> This way, the code is more readable and safer.
> 
> This code was detected with the help of Coccinelle, and audited and
> modified manually.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
> Link: https://github.com/KSPP/linux/issues/160 [2]
> Signed-off-by: Erick Archer <erick.archer@outlook.com>
> ---
> Hi,
> 
> The Coccinelle script used to detect this code pattern is the following:
> 
> virtual report
> 
> @rule1@
> type t1;
> type t2;
> identifier i0;
> identifier i1;
> identifier i2;
> identifier ALLOC =~ "kmalloc|kzalloc|kmalloc_node|kzalloc_node|vmalloc|vzalloc|kvmalloc|kvzalloc";
> position p1;
> @@
> 
> i0 = sizeof(t1) + sizeof(t2) * i1;
> ...
> i2 = ALLOC@p1(..., i0, ...);
> 
> @script:python depends on report@
> p1 << rule1.p1;
> @@
> 
> msg = "WARNING: verify allocation on line %s" % (p1[0].line)
> coccilib.report.print_report(p1[0],msg)
> 
> Regards,
> Erick
> ---
>  drivers/input/ff-core.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/input/ff-core.c b/drivers/input/ff-core.c
> index 16231fe080b0..609a5f01761b 100644
> --- a/drivers/input/ff-core.c
> +++ b/drivers/input/ff-core.c
> @@ -9,8 +9,10 @@
>  /* #define DEBUG */
>  
>  #include <linux/input.h>
> +#include <linux/limits.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
> +#include <linux/overflow.h>
>  #include <linux/sched.h>
>  #include <linux/slab.h>
>  
> @@ -315,9 +317,8 @@ int input_ff_create(struct input_dev *dev, unsigned int max_effects)
>  		return -EINVAL;
>  	}
>  
> -	ff_dev_size = sizeof(struct ff_device) +
> -				max_effects * sizeof(struct file *);
> -	if (ff_dev_size < max_effects) /* overflow */
> +	ff_dev_size = struct_size(ff, effect_owners, max_effects);
> +	if (ff_dev_size == SIZE_MAX) /* overflow */
>  		return -EINVAL;
>  
>  	ff = kzalloc(ff_dev_size, GFP_KERNEL);
> -- 
> 2.25.1
> 

Yup, thanks. This looks right to me.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook