2020-05-14 18:06:13

by Amol Grover

Subject: [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning

ipmr_for_each_table() macro uses list_for_each_entry_rcu()
for traversing outside of an RCU read side critical section
but under the protection of rtnl_mutex. Hence, add the
corresponding lockdep expression to silence the following
false-positive warning at boot:

[ 4.319347] =============================
[ 4.319349] WARNING: suspicious RCU usage
[ 4.319351] 5.5.4-stable #17 Tainted: G E
[ 4.319352] -----------------------------
[ 4.319354] net/ipv4/ipmr.c:1757 RCU-list traversed in non-reader section!!

Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
Signed-off-by: Amol Grover <[email protected]>
---
v2:
- Add appropriate Fixes tag

net/ipv4/ipmr.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 9cf83cc85e4a..4897f7420c8f 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -110,7 +110,8 @@ 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)
+ list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
+ lockdep_rtnl_is_held())

static struct mr_table *ipmr_mr_table_iter(struct net *net,
struct mr_table *mrt)
--
2.24.1

2020-05-14 18:06:57

by Amol Grover

Subject: [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro

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: [email protected]
Suggested-by: Jakub Kicinski <[email protected]>
Signed-off-by: Amol Grover <[email protected]>
---
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

2020-05-15 01:05:57

by David Miller

Subject: Re: [PATCH net v2 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro

From: Amol Grover <[email protected]>
Date: Thu, 14 May 2020 23:31:03 +0530

> 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: [email protected]
> Suggested-by: Jakub Kicinski <[email protected]>
> Signed-off-by: Amol Grover <[email protected]>

Applied.

2020-05-15 02:02:50

by David Miller

Subject: Re: [PATCH net v2 1/2] ipmr: Fix RCU list debugging warning

From: Amol Grover <[email protected]>
Date: Thu, 14 May 2020 23:31:02 +0530

> ipmr_for_each_table() macro uses list_for_each_entry_rcu()
> for traversing outside of an RCU read side critical section
> but under the protection of rtnl_mutex. Hence, add the
> corresponding lockdep expression to silence the following
> false-positive warning at boot:
>
> [ 4.319347] =============================
> [ 4.319349] WARNING: suspicious RCU usage
> [ 4.319351] 5.5.4-stable #17 Tainted: G E
> [ 4.319352] -----------------------------
> [ 4.319354] net/ipv4/ipmr.c:1757 RCU-list traversed in non-reader section!!
>
> Fixes: f0ad0860d01e ("ipv4: ipmr: support multiple tables")
> Signed-off-by: Amol Grover <[email protected]>

Applied.