[PATCH 4.19 064/103] netfilter: nf_tables: fix flowtable list del corruption

Greg Kroah-Hartman
2020-01-22T09:44:06Z

From: Florian Westphal <fw@strlen.de>

commit 335178d5429c4cee61b58f4ac80688f556630818 upstream.

syzbot reported following crash:

list_del corruption, ffff88808c9bb000->prev is LIST_POISON2 (dead000000000122)
[..]
Call Trace:
__list_del_entry include/linux/list.h:131 [inline]
list_del_rcu include/linux/rculist.h:148 [inline]
nf_tables_commit+0x1068/0x3b30 net/netfilter/nf_tables_api.c:7183
[..]

The commit transaction list has:

NFT_MSG_NEWTABLE
NFT_MSG_NEWFLOWTABLE
NFT_MSG_DELFLOWTABLE
NFT_MSG_DELTABLE

A missing generation check during DELTABLE processing causes it to queue
the DELFLOWTABLE operation a second time, so we corrupt the list here:

case NFT_MSG_DELFLOWTABLE:
list_del_rcu(&nft_trans_flowtable(trans)->list);
nf_tables_flowtable_notify(&trans->ctx,

because we have two different DELFLOWTABLE transactions for the same
flowtable. We then call list_del_rcu() twice for the same flowtable->list.

The object handling seems to suffer from the same bug so add a generation
check too and only queue delete transactions for flowtables/objects that
are still active in the next generation.

Reported-by: syzbot+37a6804945a3a13b1572@syzkaller.appspotmail.com
Fixes: 3b49e2e94e6eb ("netfilter: nf_tables: add flow table netlink frontend")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/netfilter/nf_tables_api.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -936,12 +936,18 @@ static int nft_flush_table(struct nft_ct
}

list_for_each_entry_safe(flowtable, nft, &ctx->table->flowtables, list) {
+ if (!nft_is_active_next(ctx->net, flowtable))
+ continue;
+
err = nft_delflowtable(ctx, flowtable);
if (err < 0)
goto out;
}

list_for_each_entry_safe(obj, ne, &ctx->table->objects, list) {
+ if (!nft_is_active_next(ctx->net, obj))
+ continue;
+
err = nft_delobj(ctx, obj);
if (err < 0)
goto out;