From 7013908c2db285cd6b48fcd427a56354beac2233 Mon Sep 17 00:00:00 2001 From: Amol Grover Date: Thu, 14 May 2020 23:31:03 +0530 Subject: [PATCH] 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: syzbot+1519f497f2f9f08183c6@syzkaller.appspotmail.com Suggested-by: Jakub Kicinski Signed-off-by: Amol Grover Signed-off-by: David S. Miller --- 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)