From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Florian Westphal <fw@strlen.de>
Cc: netfilter-devel@vger.kernel.org, netdev@vger.kernel.org,
syzkaller-bugs@googlegroups.com,
syzbot+156a04714799b1d480bc@syzkaller.appspotmail.com
Subject: Re: [PATCH nf] netfilter: nf_tables: check for valid chain type pointer before dereference
Date: Sat, 18 Jan 2020 21:30:57 +0100 [thread overview]
Message-ID: <20200118203057.6stoe6axtyoxfcxz@salvia> (raw)
In-Reply-To: <20200116211109.9119-1-fw@strlen.de>
On Thu, Jan 16, 2020 at 10:11:09PM +0100, Florian Westphal wrote:
> Its possible to create tables in a family that isn't supported/known.
> Then, when adding a base chain, the table pointer can be NULL.
>
> This gets us a NULL ptr dereference in nf_tables_addchain().
>
> Fixes: baae3e62f31618 ("netfilter: nf_tables: fix chain type module reference handling")
> Reported-by: syzbot+156a04714799b1d480bc@syzkaller.appspotmail.com
> Signed-off-by: Florian Westphal <fw@strlen.de>
> ---
> net/netfilter/nf_tables_api.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
> index 65f51a2e9c2a..e8976128cdb1 100644
> --- a/net/netfilter/nf_tables_api.c
> +++ b/net/netfilter/nf_tables_api.c
> @@ -953,6 +953,9 @@ static int nf_tables_newtable(struct net *net, struct sock *nlsk,
> struct nft_ctx ctx;
> int err;
>
> + if (family >= NFPROTO_NUMPROTO)
> + return -EAFNOSUPPORT;
> +
> lockdep_assert_held(&net->nft.commit_mutex);
> attr = nla[NFTA_TABLE_NAME];
> table = nft_table_lookup(net, attr, family, genmask);
> @@ -1765,6 +1768,9 @@ static int nft_chain_parse_hook(struct net *net,
> ha[NFTA_HOOK_PRIORITY] == NULL)
> return -EINVAL;
>
> + if (family >= NFPROTO_NUMPROTO)
> + return -EAFNOSUPPORT;
> +
> hook->num = ntohl(nla_get_be32(ha[NFTA_HOOK_HOOKNUM]));
> hook->priority = ntohl(nla_get_be32(ha[NFTA_HOOK_PRIORITY]));
>
> @@ -1774,6 +1780,8 @@ static int nft_chain_parse_hook(struct net *net,
> family, autoload);
> if (IS_ERR(type))
> return PTR_ERR(type);
> + } else if (!type) {
> + return -EOPNOTSUPP;
I think this check should be enough.
I mean, NFPROTO_NUMPROTO still allows for creating tables for families
that don't exist (<= NFPROTO_NUMPROTO) and why bother on creating such
table. As long as such table does not crash the kernel, I think it's
fine. No changes can be attached anymore anyway.
Otherwise, if a helper function to check for the families that are
really supported could be another alternative. But not sure it is
worth?
Let me know, thanks.
next prev parent reply other threads:[~2020-01-18 20:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-15 20:51 general protection fault in nft_chain_parse_hook syzbot
2020-01-16 18:03 ` syzbot
2020-01-16 21:11 ` [PATCH nf] netfilter: nf_tables: check for valid chain type pointer before dereference Florian Westphal
2020-01-18 20:30 ` Pablo Neira Ayuso [this message]
2020-01-18 23:28 ` Florian Westphal
2020-01-21 13:26 ` Pablo Neira Ayuso
2020-01-21 14:35 ` Florian Westphal
2020-01-17 18:57 ` general protection fault in nft_chain_parse_hook syzbot
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