Subject: Re: [Patch nf 1/3] xt_hashlimit: avoid OOM for user-controlled vmalloc

From: Florian Westphal <[email-masked]>
Date: Fri, 31 Jan 2020 23:08:56 +0100

Cong Wang <[email-masked]> wrote:
> The hashtable size could be controlled by user, so use flags
> GFP_USER | __GFP_NOWARN to avoid OOM warning triggered by user-space.
> 
> Also add __GFP_NORETRY to avoid retrying, as this is just a
> best effort and the failure is already handled gracefully.
> 
> Reported-and-tested-by: [email-masked]
> Cc: Pablo Neira Ayuso <[email-masked]>
> Cc: Jozsef Kadlecsik <[email-masked]>
> Cc: Florian Westphal <[email-masked]>
> Signed-off-by: Cong Wang <[email-masked]>
> ---
>  net/netfilter/xt_hashlimit.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
> index bccd47cd7190..885a266d8e57 100644
> --- a/net/netfilter/xt_hashlimit.c
> +++ b/net/netfilter/xt_hashlimit.c
> @@ -293,8 +293,9 @@ static int htable_create(struct net *net, struct hashlimit_cfg3 *cfg,
>  		if (size < 16)
>  			size = 16;
>  	}
> -	/* FIXME: don't use vmalloc() here or anywhere else -HW */
> -	hinfo = vmalloc(struct_size(hinfo, hash, size));
> +	/* FIXME: don't use __vmalloc() here or anywhere else -HW */
> +	hinfo = __vmalloc(struct_size(hinfo, hash, size),
> +			  GFP_USER | __GFP_NOWARN | __GFP_NORETRY, PAGE_KERNEL);

Rationale looks sane, wonder if it makes sense to drop Haralds comment
though, I don't see what other solution other than vmalloc could be used
here.