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From: Amol Grover <frextrite@gmail.com>
To: "David S . Miller" <davem@davemloft.net>,
	Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	Jakub Kicinski <kuba@kernel.org>,
	Patrick McHardy <kaber@trash.net>,
	Stephen Rothwell <sfr@canb.auug.org.au>, Qian Cai <cai@lca.pw>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
	netdev@vger.kernel.org,
	syzbot+1519f497f2f9f08183c6@syzkaller.appspotmail.com,
	linux-kernel@vger.kernel.org,
	Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: [Linux-kernel-mentees] [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro
Date: Thu, 14 May 2020 23:31:03 +0530	[thread overview]
Message-ID: <20200514180102.26425-2-frextrite@gmail.com> (raw)
In-Reply-To: <20200514180102.26425-1-frextrite@gmail.com>

During the initialization process, ipmr_new_table() is called
to create new tables which in turn calls ipmr_get_table() which
traverses net->ipv4.mr_tables without holding the writer lock.
However, this is safe to do so as no tables exist at this time.
Hence add a suitable lockdep expression to silence the following
false-positive warning:

=============================
WARNING: suspicious RCU usage
5.7.0-rc3-next-20200428-syzkaller #0 Not tainted
-----------------------------
net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!

ipmr_get_table+0x130/0x160 net/ipv4/ipmr.c:136
ipmr_new_table net/ipv4/ipmr.c:403 [inline]
ipmr_rules_init net/ipv4/ipmr.c:248 [inline]
ipmr_net_init+0x133/0x430 net/ipv4/ipmr.c:3089

Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
Reported-by: syzbot+1519f497f2f9f08183c6@syzkaller.appspotmail.com
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Amol Grover <frextrite@gmail.com>
---
v2:
- Change the lockdep expression to check for list emptiness at init
- Add Fixes tag
- Add Reported-by tag for syzbot report

 net/ipv4/ipmr.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 4897f7420c8f..5c218db2dede 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -109,9 +109,10 @@ static void mroute_clean_tables(struct mr_table *mrt, int flags);
 static void ipmr_expire_process(struct timer_list *t);
 
 #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
-#define ipmr_for_each_table(mrt, net) \
-	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
-				lockdep_rtnl_is_held())
+#define ipmr_for_each_table(mrt, net)					\
+	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list,	\
+				lockdep_rtnl_is_held() ||		\
+				list_empty(&net->ipv4.mr_tables))
 
 static struct mr_table *ipmr_mr_table_iter(struct net *net,
 					   struct mr_table *mrt)
-- 
2.24.1

_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

WARNING: multiple messages have this Message-ID (diff)
From: Amol Grover <frextrite@gmail.com>
To: "David S . Miller" <davem@davemloft.net>,
	Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	Jakub Kicinski <kuba@kernel.org>,
	Patrick McHardy <kaber@trash.net>,
	Stephen Rothwell <sfr@canb.auug.org.au>, Qian Cai <cai@lca.pw>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	Joel Fernandes <joel@joelfernandes.org>,
	Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Amol Grover <frextrite@gmail.com>,
	syzbot+1519f497f2f9f08183c6@syzkaller.appspotmail.com
Subject: [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro
Date: Thu, 14 May 2020 23:31:03 +0530	[thread overview]
Message-ID: <20200514180102.26425-2-frextrite@gmail.com> (raw)
In-Reply-To: <20200514180102.26425-1-frextrite@gmail.com>

During the initialization process, ipmr_new_table() is called
to create new tables which in turn calls ipmr_get_table() which
traverses net->ipv4.mr_tables without holding the writer lock.
However, this is safe to do so as no tables exist at this time.
Hence add a suitable lockdep expression to silence the following
false-positive warning:

=============================
WARNING: suspicious RCU usage
5.7.0-rc3-next-20200428-syzkaller #0 Not tainted
-----------------------------
net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!

ipmr_get_table+0x130/0x160 net/ipv4/ipmr.c:136
ipmr_new_table net/ipv4/ipmr.c:403 [inline]
ipmr_rules_init net/ipv4/ipmr.c:248 [inline]
ipmr_net_init+0x133/0x430 net/ipv4/ipmr.c:3089

Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
Reported-by: syzbot+1519f497f2f9f08183c6@syzkaller.appspotmail.com
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Amol Grover <frextrite@gmail.com>
---
v2:
- Change the lockdep expression to check for list emptiness at init
- Add Fixes tag
- Add Reported-by tag for syzbot report

 net/ipv4/ipmr.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 4897f7420c8f..5c218db2dede 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -109,9 +109,10 @@ static void mroute_clean_tables(struct mr_table *mrt, int flags);
 static void ipmr_expire_process(struct timer_list *t);
 
 #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
-#define ipmr_for_each_table(mrt, net) \
-	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
-				lockdep_rtnl_is_held())
+#define ipmr_for_each_table(mrt, net)					\
+	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list,	\
+				lockdep_rtnl_is_held() ||		\
+				list_empty(&net->ipv4.mr_tables))
 
 static struct mr_table *ipmr_mr_table_iter(struct net *net,
 					   struct mr_table *mrt)
-- 
2.24.1


  reply	other threads:[~2020-05-14 18:02 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-14 18:01 [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning Amol Grover
2020-05-14 18:01 ` Amol Grover
2020-05-14 18:01 ` Amol Grover [this message]
2020-05-14 18:01   ` [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro Amol Grover
2020-05-15  1:01   ` [Linux-kernel-mentees] " David Miller
2020-05-15  1:01     ` David Miller
2020-05-15  1:01 ` [Linux-kernel-mentees] [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning David Miller
2020-05-15  1:01   ` David Miller

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