From: Florian Westphal fw@strlen.de
[ Upstream commit edbd82c5fba009f68d20b5db585be1e667c605f6 ]
Following splat gets triggered when nfnetlink monitor is running while xtables-nft selftests are running:
net/netfilter/nf_tables_api.c:1272 suspicious rcu_dereference_check() usage! other info that might help us debug this:
1 lock held by xtables-nft-mul/27006: #0: 00000000e0f85be9 (&net->nft.commit_mutex){+.+.}, at: nf_tables_valid_genid+0x1a/0x50 Call Trace: nf_tables_fill_chain_info.isra.45+0x6cc/0x6e0 nf_tables_chain_notify+0xf8/0x1a0 nf_tables_commit+0x165c/0x1740
nf_tables_fill_chain_info() can be called both from dumps (rcu read locked) or from the transaction path if a userspace process subscribed to nftables notifications.
In the 'table dump' case, rcu_access_pointer() cannot be used: We do not hold transaction mutex so the pointer can be NULLed right after the check. Just unconditionally fetch the value, then have the helper return immediately if its NULL.
In the notification case we don't hold the rcu read lock, but updates are prevented due to transaction mutex. Use rcu_dereference_check() to make lockdep aware of this.
Signed-off-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 | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c index ebfcfe1dcbdbb..29ff59dd99ace 100644 --- a/net/netfilter/nf_tables_api.c +++ b/net/netfilter/nf_tables_api.c @@ -1142,6 +1142,9 @@ static int nft_dump_stats(struct sk_buff *skb, struct nft_stats __percpu *stats) u64 pkts, bytes; int cpu;
+ if (!stats) + return 0; + memset(&total, 0, sizeof(total)); for_each_possible_cpu(cpu) { cpu_stats = per_cpu_ptr(stats, cpu); @@ -1199,6 +1202,7 @@ static int nf_tables_fill_chain_info(struct sk_buff *skb, struct net *net, if (nft_is_base_chain(chain)) { const struct nft_base_chain *basechain = nft_base_chain(chain); const struct nf_hook_ops *ops = &basechain->ops; + struct nft_stats __percpu *stats; struct nlattr *nest;
nest = nla_nest_start(skb, NFTA_CHAIN_HOOK); @@ -1220,8 +1224,9 @@ static int nf_tables_fill_chain_info(struct sk_buff *skb, struct net *net, if (nla_put_string(skb, NFTA_CHAIN_TYPE, basechain->type->name)) goto nla_put_failure;
- if (rcu_access_pointer(basechain->stats) && - nft_dump_stats(skb, rcu_dereference(basechain->stats))) + stats = rcu_dereference_check(basechain->stats, + lockdep_commit_lock_is_held(net)); + if (nft_dump_stats(skb, stats)) goto nla_put_failure; }