2020-03-25 14:34:39

by Qian Cai

Subject: [PATCH] netfilter/nf_tables: silence a RCU-list warning

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 <[email protected]>
---
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 38c680f28f15..e398d1491057 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))
--
2.21.0 (Apple Git-122.2)

2020-03-25 23:14:28

by Florian Westphal

Subject: Re: [PATCH] netfilter/nf_tables: silence a RCU-list warning

Qian Cai <[email protected]> wrote:
> 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,

[..]

> - 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)) {

Thanks for the patch.

Acked-by: Florian Westphal <[email protected]>

2020-03-26 13:47:11

by Pablo Neira Ayuso

Subject: Re: [PATCH] netfilter/nf_tables: silence a RCU-list warning

On Wed, Mar 25, 2020 at 10:31:42AM -0400, Qian Cai wrote:
> 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!!

Applied, thanks.