Re: [PATCH net] ipvs: prevent integer overflow in do_ip_vs_get_ctl()

[Julian Anastasov <ja@ssi.bg>]

	Hello,

On Fri, 7 Mar 2025, Dan Carpenter wrote:

> The get->num_services variable is an unsigned int which is controlled by
> the user.  The struct_size() function ensures that the size calculation
> does not overflow an unsigned long, however, we are saving the result to
> an int so the calculation can overflow.
> 
> Save the result from struct_size() type size_t to fix this integer
> overflow bug.
> 
> Cc: stable@vger.kernel.org
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
> ---
>  net/netfilter/ipvs/ip_vs_ctl.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
> index 7d13110ce188..801d65fd8a81 100644
> --- a/net/netfilter/ipvs/ip_vs_ctl.c
> +++ b/net/netfilter/ipvs/ip_vs_ctl.c
> @@ -3091,12 +3091,12 @@ do_ip_vs_get_ctl(struct sock *sk, int cmd, void __user *user, int *len)
>  	case IP_VS_SO_GET_SERVICES:
>  	{
>  		struct ip_vs_get_services *get;
> -		int size;
> +		size_t size;
>  
>  		get = (struct ip_vs_get_services *)arg;
>  		size = struct_size(get, entrytable, get->num_services);

	Both are GET operations. The problem that can happen only
on 64-bit platforms is that user will attempt copy_to_user() with
shorter buffer and will get EFAULT if there are so many entries to
return. On 32-bit size will be -1 and will not match *len (EINVAL).
So, I assume the issue is not critical, right?

>  		if (*len != size) {
> -			pr_err("length: %u != %u\n", *len, size);
> +			pr_err("length: %u != %lu\n", *len, size);

	%zu, %lu fails on 32-bit platforms. Please, send v2
fixing the format.

>  			ret = -EINVAL;
>  			goto out;
>  		}
> @@ -3132,12 +3132,12 @@ do_ip_vs_get_ctl(struct sock *sk, int cmd, void __user *user, int *len)
>  	case IP_VS_SO_GET_DESTS:
>  	{
>  		struct ip_vs_get_dests *get;
> -		int size;
> +		size_t size;
>  
>  		get = (struct ip_vs_get_dests *)arg;
>  		size = struct_size(get, entrytable, get->num_dests);
>  		if (*len != size) {
> -			pr_err("length: %u != %u\n", *len, size);
> +			pr_err("length: %u != %lu\n", *len, size);
>  			ret = -EINVAL;
>  			goto out;
>  		}
> -- 
> 2.47.2

Regards

--
Julian Anastasov <ja@ssi.bg>