[PATCH AUTOSEL 4.19 20/97] netfilter: nf_tables: fix suspicious RCU usage in nft_chain_stats_replace()

Sasha Levin
2018-12-26T23:00:59Z

From: Taehee Yoo <ap420073@gmail.com>

[ Upstream commit 4c05ec47384ab3627b62814e8f886e90cc38ce15 ]

basechain->stats is rcu protected data which is updated from
nft_chain_stats_replace(). This function is executed from the commit
phase which holds the pernet nf_tables commit mutex - not the global
nfnetlink subsystem mutex.

Test commands to reproduce the problem are:
%iptables-nft -I INPUT
%iptables-nft -Z
%iptables-nft -Z

This patch uses RCU calls to handle basechain->stats updates to fix a
splat that looks like:

[89279.358755] =============================
[89279.363656] WARNING: suspicious RCU usage
[89279.368458] 4.20.0-rc2+ #44 Tainted: G W L
[89279.374661] -----------------------------
[89279.379542] net/netfilter/nf_tables_api.c:1404 suspicious rcu_dereference_protected() usage!
[...]
[89279.406556] 1 lock held by iptables-nft/5225:
[89279.411728] #0: 00000000bf45a000 (&net->nft.commit_mutex){+.+.}, at: nf_tables_valid_genid+0x1f/0x70 [nf_tables]
[89279.424022] stack backtrace:
[89279.429236] CPU: 0 PID: 5225 Comm: iptables-nft Tainted: G W L 4.20.0-rc2+ #44
[89279.430135] Call Trace:
[89279.430135] dump_stack+0xc9/0x16b
[89279.430135] ? show_regs_print_info+0x5/0x5
[89279.430135] ? lockdep_rcu_suspicious+0x117/0x160
[89279.430135] nft_chain_commit_update+0x4ea/0x640 [nf_tables]
[89279.430135] ? sched_clock_local+0xd4/0x140
[89279.430135] ? check_flags.part.35+0x440/0x440
[89279.430135] ? __rhashtable_remove_fast.constprop.67+0xec0/0xec0 [nf_tables]
[89279.430135] ? sched_clock_cpu+0x126/0x170
[89279.430135] ? find_held_lock+0x39/0x1c0
[89279.430135] ? hlock_class+0x140/0x140
[89279.430135] ? is_bpf_text_address+0x5/0xf0
[89279.430135] ? check_flags.part.35+0x440/0x440
[89279.430135] ? __lock_is_held+0xb4/0x140
[89279.430135] nf_tables_commit+0x2555/0x39c0 [nf_tables]

Fixes: f102d66b335a4 ("netfilter: nf_tables: use dedicated mutex to guard transactions")
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/netfilter/nfnetlink.h | 12 ------------
net/netfilter/nf_tables_api.c | 21 +++++++++++++--------
net/netfilter/nf_tables_core.c | 2 +-
3 files changed, 14 insertions(+), 21 deletions(-)

diff --git a/include/linux/netfilter/nfnetlink.h b/include/linux/netfilter/nfnetlink.h
index 4a520d3304a2..cf09ab37b45b 100644
--- a/include/linux/netfilter/nfnetlink.h
+++ b/include/linux/netfilter/nfnetlink.h
@@ -62,18 +62,6 @@ static inline bool lockdep_nfnl_is_held(__u8 subsys_id)
}
#endif /* CONFIG_PROVE_LOCKING */

-/*
- * nfnl_dereference - fetch RCU pointer when updates are prevented by subsys mutex
- *
- * @p: The pointer to read, prior to dereferencing
- * @ss: The nfnetlink subsystem ID
- *
- * Return the value of the specified RCU-protected pointer, but omit
- * the READ_ONCE(), because caller holds the NFNL subsystem mutex.
- */
-#define nfnl_dereference(p, ss) \
- rcu_dereference_protected(p, lockdep_nfnl_is_held(ss))
-
#define MODULE_ALIAS_NFNL_SUBSYS(subsys) \
MODULE_ALIAS("nfnetlink-subsys-" __stringify(subsys))

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index fe0558b15fd3..ed9af46720e1 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -1199,7 +1199,8 @@ 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 (basechain->stats && nft_dump_stats(skb, basechain->stats))
+ if (rcu_access_pointer(basechain->stats) &&
+ nft_dump_stats(skb, rcu_dereference(basechain->stats)))
goto nla_put_failure;
}

@@ -1375,7 +1376,8 @@ static struct nft_stats __percpu *nft_stats_alloc(const struct nlattr *attr)
return newstats;
}

-static void nft_chain_stats_replace(struct nft_base_chain *chain,
+static void nft_chain_stats_replace(struct net *net,
+ struct nft_base_chain *chain,
struct nft_stats __percpu *newstats)
{
struct nft_stats __percpu *oldstats;
@@ -1383,8 +1385,9 @@ static void nft_chain_stats_replace(struct nft_base_chain *chain,
if (newstats == NULL)
return;

- if (chain->stats) {
- oldstats = nfnl_dereference(chain->stats, NFNL_SUBSYS_NFTABLES);
+ if (rcu_access_pointer(chain->stats)) {
+ oldstats = rcu_dereference_protected(chain->stats,
+ lockdep_commit_lock_is_held(net));
rcu_assign_pointer(chain->stats, newstats);
synchronize_rcu();
free_percpu(oldstats);
@@ -1421,9 +1424,10 @@ static void nf_tables_chain_destroy(struct nft_ctx *ctx)
struct nft_base_chain *basechain = nft_base_chain(chain);

module_put(basechain->type->owner);
- free_percpu(basechain->stats);
- if (basechain->stats)
+ if (rcu_access_pointer(basechain->stats)) {
static_branch_dec(&nft_counters_enabled);
+ free_percpu(rcu_dereference_raw(basechain->stats));
+ }
kfree(chain->name);
kfree(basechain);
} else {
@@ -1572,7 +1576,7 @@ static int nf_tables_addchain(struct nft_ctx *ctx, u8 family, u8 genmask,
kfree(basechain);
return PTR_ERR(stats);
}
- basechain->stats = stats;
+ rcu_assign_pointer(basechain->stats, stats);
static_branch_inc(&nft_counters_enabled);
}

@@ -6145,7 +6149,8 @@ static void nft_chain_commit_update(struct nft_trans *trans)
return;

basechain = nft_base_chain(trans->ctx.chain);
- nft_chain_stats_replace(basechain, nft_trans_chain_stats(trans));
+ nft_chain_stats_replace(trans->ctx.net, basechain,
+ nft_trans_chain_stats(trans));

switch (nft_trans_chain_policy(trans)) {
case NF_DROP:
diff --git a/net/netfilter/nf_tables_core.c b/net/netfilter/nf_tables_core.c
index ffd5c0f9412b..60f258f2c707 100644
--- a/net/netfilter/nf_tables_core.c
+++ b/net/netfilter/nf_tables_core.c
@@ -101,7 +101,7 @@ static noinline void nft_update_chain_stats(const struct nft_chain *chain,
struct nft_stats *stats;

base_chain = nft_base_chain(chain);
- if (!base_chain->stats)
+ if (!rcu_access_pointer(base_chain->stats))
return;

local_bh_disable();
--
2.19.1