linux-kernel - Re: [PATCH 4.19 67/92] netfilter: nf_tables: add __nft_chain_type

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Date:   Tue, 28 Jan 2020 19:13:01 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        syzbot+156a04714799b1d480bc@...kaller.appspotmail.com,
        Pablo Neira Ayuso <pablo@...filter.org>
Subject: Re: [PATCH 4.19 67/92] netfilter: nf_tables: add
 __nft_chain_type_get()

Hi!

> From: Pablo Neira Ayuso <pablo@...filter.org>
> 
> commit 826035498ec14b77b62a44f0cb6b94d45530db6f upstream.
> 
> This new helper function validates that unknown family and chain type
> coming from userspace do not trigger an out-of-bound array access. Bail
> out in case __nft_chain_type_get() returns NULL from
> nft_chain_parse_hook().

> +++ b/net/netfilter/nf_tables_api.c
> @@ -472,14 +472,27 @@ static inline u64 nf_tables_alloc_handle
>  static const struct nft_chain_type *chain_type[NFPROTO_NUMPROTO][NFT_CHAIN_T_MAX];
>  
>  static const struct nft_chain_type *
> +__nft_chain_type_get(u8 family, enum nft_chain_types type)
> +{
> +	if (family >= NFPROTO_NUMPROTO ||
> +	    type >= NFT_CHAIN_T_MAX)
> +		return NULL;
> +
> +	return chain_type[family][type];
> +}

Are enum types guaranteed to be unsigned on all compilers we care
about? Google says they can be signed, too. So, should the test be
"((unsigned int) type) >= ..." ?

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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