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netfilter: nf_tables: fix suspicious RCU usage in nft_chain_stats_rep…
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…lace()

[ Upstream commit 4c05ec4 ]

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: f102d66 ("netfilter: nf_tables: use dedicated mutex to guard transactions")
Signed-off-by: Taehee Yoo <[email protected]>
Signed-off-by: Pablo Neira Ayuso <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
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TaeheeYoo authored and gregkh committed Jan 13, 2019
1 parent 537e9a8 commit cee05c0
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Showing 3 changed files with 14 additions and 21 deletions.
12 changes: 0 additions & 12 deletions include/linux/netfilter/nfnetlink.h
Original file line number Diff line number Diff line change
Expand Up @@ -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))

Expand Down
21 changes: 13 additions & 8 deletions net/netfilter/nf_tables_api.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
}

Expand Down Expand Up @@ -1375,16 +1376,18 @@ 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;

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);
Expand Down Expand Up @@ -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 {
Expand Down Expand Up @@ -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);
}

Expand Down Expand Up @@ -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:
Expand Down
2 changes: 1 addition & 1 deletion net/netfilter/nf_tables_core.c
Original file line number Diff line number Diff line change
Expand Up @@ -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();
Expand Down

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