Commit 9f6958ba authored by Florian Westphal's avatar Florian Westphal Committed by Pablo Neira Ayuso

netfilter: nf_tables: unconditionally flush pending work before notifier

syzbot reports:

KASAN: slab-uaf in nft_ctx_update include/net/netfilter/nf_tables.h:1831
KASAN: slab-uaf in nft_commit_release net/netfilter/nf_tables_api.c:9530
KASAN: slab-uaf int nf_tables_trans_destroy_work+0x152b/0x1750 net/netfilter/nf_tables_api.c:9597
Read of size 2 at addr ffff88802b0051c4 by task kworker/1:1/45
[..]
Workqueue: events nf_tables_trans_destroy_work
Call Trace:
 nft_ctx_update include/net/netfilter/nf_tables.h:1831 [inline]
 nft_commit_release net/netfilter/nf_tables_api.c:9530 [inline]
 nf_tables_trans_destroy_work+0x152b/0x1750 net/netfilter/nf_tables_api.c:9597

Problem is that the notifier does a conditional flush, but its possible
that the table-to-be-removed is still referenced by transactions being
processed by the worker, so we need to flush unconditionally.

We could make the flush_work depend on whether we found a table to delete
in nf-next to avoid the flush for most cases.

AFAICS this problem is only exposed in nf-next, with
commit e169285f ("netfilter: nf_tables: do not store nft_ctx in transaction objects"),
with this commit applied there is an unconditional fetch of
table->family which is whats triggering the above splat.

Fixes: 2c9f0293 ("netfilter: nf_tables: flush pending destroy work before netlink notifier")
Reported-and-tested-by: syzbot+4fd66a69358fc15ae2ad@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4fd66a69358fc15ae2adSigned-off-by: default avatarFlorian Westphal <fw@strlen.de>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent 8905a2c7
......@@ -11483,8 +11483,7 @@ static int nft_rcv_nl_event(struct notifier_block *this, unsigned long event,
gc_seq = nft_gc_seq_begin(nft_net);
if (!list_empty(&nf_tables_destroy_list))
nf_tables_trans_destroy_flush_work();
nf_tables_trans_destroy_flush_work();
again:
list_for_each_entry(table, &nft_net->tables, list) {
if (nft_table_has_owner(table) &&
......
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