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Date:   Sat, 11 Apr 2020 19:06:40 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Qian Cai <cai@....pw>, Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Sasha Levin <sashal@...nel.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 5.5 095/121] netfilter: nf_tables: silence a RCU-list warning in nft_table_lookup()

From: Qian Cai <cai@....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@....pw>
Acked-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Sasha Levin <sashal@...nel.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 11a2a7b5312ee..61c544801e534 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -520,7 +520,8 @@ 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))
-- 
2.20.1

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