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netfilter: nft_ct: protect nft_ct_pcpu_template_refcnt with mutex

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Syzbot hit use-after-free in nf_tables_dump_sets. The problem was in
missing lock protection for nft_ct_pcpu_template_refcnt.

Before commit f102d66b33 ("netfilter: nf_tables: use dedicated
mutex to guard transactions") all transactions were serialized by global
mutex, but then global mutex was changed to local per netnamespace
commit_mutex.

This change causes use-after-free bug, when 2 netnamespaces concurently
changing nft_ct_pcpu_template_refcnt without proper locking. Fix it by
adding nft_ct_pcpu_mutex and protect all nft_ct_pcpu_template_refcnt
changes with it.

Fixes: f102d66b33 ("netfilter: nf_tables: use dedicated mutex to guard transactions")
Reported-and-tested-by: syzbot+649e339fa6658ee623d3@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Pavel Skripkin 2021-08-10 15:59:20 +03:00 committed by Pablo Neira Ayuso
parent 519133debc
commit e3245a7b7b
1 changed files with 8 additions and 1 deletions
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9
net/netfilter/nft_ct.c
View file

@ -41,6 +41,7 @@ struct nft_ct_helper_obj {
#ifdef CONFIG_NF_CONNTRACK_ZONES
static DEFINE_PER_CPU(struct nf_conn *, nft_ct_pcpu_template);
static unsigned int nft_ct_pcpu_template_refcnt __read_mostly;
static DEFINE_MUTEX(nft_ct_pcpu_mutex);
#endif
static u64 nft_ct_get_eval_counter(const struct nf_conn_counter *c,
@ -525,8 +526,10 @@ static void __nft_ct_set_destroy(const struct nft_ctx *ctx, struct nft_ct *priv)
#endif
#ifdef CONFIG_NF_CONNTRACK_ZONES
case NFT_CT_ZONE:
mutex_lock(&nft_ct_pcpu_mutex);
if (--nft_ct_pcpu_template_refcnt == 0)
nft_ct_tmpl_put_pcpu();
mutex_unlock(&nft_ct_pcpu_mutex);
break;
#endif
default:
@ -564,9 +567,13 @@ static int nft_ct_set_init(const struct nft_ctx *ctx,
#endif
#ifdef CONFIG_NF_CONNTRACK_ZONES
case NFT_CT_ZONE:
if (!nft_ct_tmpl_alloc_pcpu())
mutex_lock(&nft_ct_pcpu_mutex);
if (!nft_ct_tmpl_alloc_pcpu()) {
mutex_unlock(&nft_ct_pcpu_mutex);
return -ENOMEM;
}
nft_ct_pcpu_template_refcnt++;
mutex_unlock(&nft_ct_pcpu_mutex);
len = sizeof(u16);
break;
#endif