[PATCH net] ipv4: convert fib_num_tclassid_users to atomic_t

From: Eric Dumazet <redacted>

Before commit faa041a40b9f ("ipv4: Create cleanup helper for fib_nh")
changes to net->ipv4.fib_num_tclassid_users were protected by RTNL.

After the change, this is no longer the case, as free_fib_info_rcu()
runs after rcu grace period, without rtnl being held.

Fixes: faa041a40b9f ("ipv4: Create cleanup helper for fib_nh")
Signed-off-by: Eric Dumazet <redacted>
Cc: David Ahern <dsahern@kernel.org>
---
 include/net/ip_fib.h     | 2 +-
 include/net/netns/ipv4.h | 2 +-
 net/ipv4/fib_frontend.c  | 2 +-
 net/ipv4/fib_rules.c     | 4 ++--
 net/ipv4/fib_semantics.c | 4 ++--
 5 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index ab5348e57db1a627cbce2dededb2e9b754d1f2cd..3417ba2d27ad6a1b5612a8855d2788f10d9fdf25 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h

@@ -438,7 +438,7 @@ int fib_validate_source(struct sk_buff *skb, __be32 src, __be32 dst,
 #ifdef CONFIG_IP_ROUTE_CLASSID
 static inline int fib_num_tclassid_users(struct net *net)
 {
-	return net->ipv4.fib_num_tclassid_users;
+	return atomic_read(&net->ipv4.fib_num_tclassid_users);
 }
 #else
 static inline int fib_num_tclassid_users(struct net *net)

diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 2f65701a43c953bd3a9a9e3d491882cb7bb11859..6c5b2efc4f17d0d17be750d0c1a2e1d169ec063e 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h

@@ -65,7 +65,7 @@ struct netns_ipv4 {
 	bool			fib_has_custom_local_routes;
 	bool			fib_offload_disabled;
 #ifdef CONFIG_IP_ROUTE_CLASSID
-	int			fib_num_tclassid_users;
+	atomic_t		fib_num_tclassid_users;
 #endif
 	struct hlist_head	*fib_table_hash;
 	struct sock		*fibnl;

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 9fe13e4f5d08a5cf9cd9ff15033b9f6e0dc9e492..4d61ddd8a0ecfc4cc47b4802eb5a573beb84ee44 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c

@@ -1582,7 +1582,7 @@ static int __net_init fib_net_init(struct net *net)
 	int error;
 
 #ifdef CONFIG_IP_ROUTE_CLASSID
-	net->ipv4.fib_num_tclassid_users = 0;
+	atomic_set(&net->ipv4.fib_num_tclassid_users, 0);
 #endif
 	error = ip_fib_net_init(net);
 	if (error < 0)

diff --git a/net/ipv4/fib_rules.c b/net/ipv4/fib_rules.c
index 364ad3446b2f3c056ea5dafea1542e4d3306ddb6..d279cb8ac1584487885f66819634b421c01bf819 100644
--- a/net/ipv4/fib_rules.c
+++ b/net/ipv4/fib_rules.c

@@ -264,7 +264,7 @@ static int fib4_rule_configure(struct fib_rule *rule, struct sk_buff *skb,
 	if (tb[FRA_FLOW]) {
 		rule4->tclassid = nla_get_u32(tb[FRA_FLOW]);
 		if (rule4->tclassid)
-			net->ipv4.fib_num_tclassid_users++;
+			atomic_inc(&net->ipv4.fib_num_tclassid_users);
 	}
 #endif
 

@@ -296,7 +296,7 @@ static int fib4_rule_delete(struct fib_rule *rule)
 
 #ifdef CONFIG_IP_ROUTE_CLASSID
 	if (((struct fib4_rule *)rule)->tclassid)
-		net->ipv4.fib_num_tclassid_users--;
+		atomic_dec(&net->ipv4.fib_num_tclassid_users);
 #endif
 	net->ipv4.fib_has_custom_rules = true;
 

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 3364cb9c67e018fea2b2e370046de5252581b996..fde7797b580694bb3924c5c6e9560cf04fd67387 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c

@@ -220,7 +220,7 @@ void fib_nh_release(struct net *net, struct fib_nh *fib_nh)
 {
 #ifdef CONFIG_IP_ROUTE_CLASSID
 	if (fib_nh->nh_tclassid)
-		net->ipv4.fib_num_tclassid_users--;
+		atomic_dec(&net->ipv4.fib_num_tclassid_users);
 #endif
 	fib_nh_common_release(&fib_nh->nh_common);
 }

@@ -632,7 +632,7 @@ int fib_nh_init(struct net *net, struct fib_nh *nh,
 #ifdef CONFIG_IP_ROUTE_CLASSID
 	nh->nh_tclassid = cfg->fc_flow;
 	if (nh->nh_tclassid)
-		net->ipv4.fib_num_tclassid_users++;
+		atomic_inc(&net->ipv4.fib_num_tclassid_users);
 #endif
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 	nh->fib_nh_weight = nh_weight;

-- 
2.34.0.rc2.393.gf8c9666880-goog

On 12/1/21 7:26 PM, Eric Dumazet wrote:

From: Eric Dumazet <redacted>

Before commit faa041a40b9f ("ipv4: Create cleanup helper for fib_nh")
changes to net->ipv4.fib_num_tclassid_users were protected by RTNL.

After the change, this is no longer the case, as free_fib_info_rcu()
runs after rcu grace period, without rtnl being held.

Fixes: faa041a40b9f ("ipv4: Create cleanup helper for fib_nh")
Signed-off-by: Eric Dumazet <redacted>
Cc: David Ahern <dsahern@kernel.org>
---
 include/net/ip_fib.h     | 2 +-
 include/net/netns/ipv4.h | 2 +-
 net/ipv4/fib_frontend.c  | 2 +-
 net/ipv4/fib_rules.c     | 4 ++--
 net/ipv4/fib_semantics.c | 4 ++--
 5 files changed, 7 insertions(+), 7 deletions(-)

Thanks, Eric. Was this found by syzbot or code inspection?

Reviewed-by: David Ahern <dsahern@kernel.org>

On Wed, Dec 1, 2021 at 6:42 PM David Ahern [off-list ref] wrote:

On 12/1/21 7:26 PM, Eric Dumazet wrote:

quoted

From: Eric Dumazet <redacted>

Before commit faa041a40b9f ("ipv4: Create cleanup helper for fib_nh")
changes to net->ipv4.fib_num_tclassid_users were protected by RTNL.

After the change, this is no longer the case, as free_fib_info_rcu()
runs after rcu grace period, without rtnl being held.

Fixes: faa041a40b9f ("ipv4: Create cleanup helper for fib_nh")
Signed-off-by: Eric Dumazet <redacted>
Cc: David Ahern <dsahern@kernel.org>
---
 include/net/ip_fib.h     | 2 +-
 include/net/netns/ipv4.h | 2 +-
 net/ipv4/fib_frontend.c  | 2 +-
 net/ipv4/fib_rules.c     | 4 ++--
 net/ipv4/fib_semantics.c | 4 ++--
 5 files changed, 7 insertions(+), 7 deletions(-)

Thanks, Eric. Was this found by syzbot or code inspection?

Code inspection, while plumbing my dev_hold_track() and dev_put_track() helpers.

Reviewed-by: David Ahern <dsahern@kernel.org>

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller [off-list ref]:

On Wed,  1 Dec 2021 18:26:35 -0800 you wrote:

From: Eric Dumazet <redacted>

Before commit faa041a40b9f ("ipv4: Create cleanup helper for fib_nh")
changes to net->ipv4.fib_num_tclassid_users were protected by RTNL.

After the change, this is no longer the case, as free_fib_info_rcu()
runs after rcu grace period, without rtnl being held.

[...]

Here is the summary with links:
  - [net] ipv4: convert fib_num_tclassid_users to atomic_t
    https://git.kernel.org/netdev/net/c/213f5f8f31f1

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html