[PATCH AUTOSEL 5.4 215/330] netfilter: nf_tables: silence a RCU-list warning in nft_table_lookup()

Sasha Levin
2020-09-18T03:00:47Z

From: Qian Cai <cai@lca.pw>

[ Upstream commit 0a6a9515fe390976cd762c52d8d4f446d7a14285 ]

It is safe to traverse &net->nft.tables with &net->nft.commit_mutex
held using list_for_each_entry_rcu(). Silence the PROVE_RCU_LIST false
positive,

WARNING: suspicious RCU usage
net/netfilter/nf_tables_api.c:523 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
1 lock held by iptables/1384:
#0: ffffffff9745c4a8 (&net->nft.commit_mutex){+.+.}, at: nf_tables_valid_genid+0x25/0x60 [nf_tables]

Call Trace:
dump_stack+0xa1/0xea
lockdep_rcu_suspicious+0x103/0x10d
nft_table_lookup.part.0+0x116/0x120 [nf_tables]
nf_tables_newtable+0x12c/0x7d0 [nf_tables]
nfnetlink_rcv_batch+0x559/0x1190 [nfnetlink]
nfnetlink_rcv+0x1da/0x210 [nfnetlink]
netlink_unicast+0x306/0x460
netlink_sendmsg+0x44b/0x770
____sys_sendmsg+0x46b/0x4a0
___sys_sendmsg+0x138/0x1a0
__sys_sendmsg+0xb6/0x130
__x64_sys_sendmsg+0x48/0x50
do_syscall_64+0x69/0xf4
entry_SYSCALL_64_after_hwframe+0x49/0xb3

Signed-off-by: Qian Cai <cai@lca.pw>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nf_tables_api.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 2023650c27249..ff2d2b514506e 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -456,7 +456,8 @@ static struct nft_table *nft_table_lookup(const struct net *net,
if (nla == NULL)
return ERR_PTR(-EINVAL);

- list_for_each_entry_rcu(table, &net->nft.tables, list) {
+ list_for_each_entry_rcu(table, &net->nft.tables, list,
+ lockdep_is_held(&net->nft.commit_mutex)) {
if (!nla_strcmp(nla, table->name) &&
table->family == family &&
nft_active_genmask(table, genmask))
--
2.25.1