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netfilter: nf_tables: unlink table before deleting it 

syzbot reports following UAF:
BUG: KASAN: use-after-free in memcmp+0x18f/0x1c0 lib/string.c:955
 nla_strcmp+0xf2/0x130 lib/nlattr.c:836
 nft_table_lookup.part.0+0x1a2/0x460 net/netfilter/nf_tables_api.c:570
 nft_table_lookup net/netfilter/nf_tables_api.c:4064 [inline]
 nf_tables_getset+0x1b3/0x860 net/netfilter/nf_tables_api.c:4064
 nfnetlink_rcv_msg+0x659/0x13f0 net/netfilter/nfnetlink.c:285
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2504

Problem is that all get operations are lockless, so the commit_mutex
held by nft_rcv_nl_event() isn't enough to stop a parallel GET request
from doing read-accesses to the table object even after synchronize_rcu().

To avoid this, unlink the table first and store the table objects in
on-stack scratch space.

Fixes: 6001a930ce ("netfilter: nftables: introduce table ownership")
Reported-and-tested-by: syzbot+f31660cf279b0557160c@syzkaller.appspotmail.com
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2021-09-13 14:42:33 +02:00 committed by Pablo Neira Ayuso
parent cb89f63ba6
commit a499b03bf3
1 changed files with 18 additions and 10 deletions
net/netfilter
nf_tables_api.c

28
net/netfilter/nf_tables_api.c
View File

@ -9599,7 +9599,6 @@ static void __nft_release_table(struct net *net, struct nft_table *table)
table->use--;
nf_tables_chain_destroy(&ctx);
}
list_del(&table->list);
nf_tables_table_destroy(&ctx);
}
@ -9612,6 +9611,8 @@ static void __nft_release_tables(struct net *net)
if (nft_table_has_owner(table))
continue;
list_del(&table->list);
__nft_release_table(net, table);
}
}
@ -9619,31 +9620,38 @@ static void __nft_release_tables(struct net *net)
static int nft_rcv_nl_event(struct notifier_block *this, unsigned long event,
void *ptr)
{
struct nft_table *table, *to_delete[8];
struct nftables_pernet *nft_net;
struct netlink_notify *n = ptr;
struct nft_table *table, *nt;
struct net *net = n->net;
bool release = false;
unsigned int deleted;
bool restart = false;
if (event != NETLINK_URELEASE || n->protocol != NETLINK_NETFILTER)
return NOTIFY_DONE;
nft_net = nft_pernet(net);
deleted = 0;
mutex_lock(&nft_net->commit_mutex);
again:
list_for_each_entry(table, &nft_net->tables, list) {
if (nft_table_has_owner(table) &&
n->portid == table->nlpid) {
__nft_release_hook(net, table);
release = true;
list_del_rcu(&table->list);
to_delete[deleted++] = table;
if (deleted >= ARRAY_SIZE(to_delete))
break;
}
}
if (release) {
if (deleted) {
restart = deleted >= ARRAY_SIZE(to_delete);
synchronize_rcu();
list_for_each_entry_safe(table, nt, &nft_net->tables, list) {
if (nft_table_has_owner(table) &&
n->portid == table->nlpid)
__nft_release_table(net, table);
}
while (deleted)
__nft_release_table(net, to_delete[--deleted]);
if (restart)
goto again;
}
mutex_unlock(&nft_net->commit_mutex);