ipv4: fix a potential deadlock in mcast getsockopt() path

Sasha reported the following lockdep warning:

  Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
   lock(sk_lock-AF_INET);
                                lock(rtnl_mutex);
                                lock(sk_lock-AF_INET);
   lock(rtnl_mutex);

This is due to that for IP_MSFILTER and MCAST_MSFILTER, we take
rtnl lock before the socket lock in setsockopt() path, but take
the socket lock before rtnl lock in getsockopt() path. All the
rest optnames are setsockopt()-only.

Fix this by aligning the getsockopt() path with the setsockopt()
path, so that all mcast socket path would be locked in the same
order.

Note, IPv6 part is different where rtnl lock is not held.

Fixes: 54ff9ef36bdf ("ipv4, ipv6: kill ip_mc_{join, leave}_group and ipv6_sock_mc_{join, drop}")
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 8 deletions

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 64aaf35..6baf36e 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -2392,11 +2392,11 @@ int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
 	struct ip_sf_socklist *psl;
 	struct net *net = sock_net(sk);
 
+	ASSERT_RTNL();
+
 	if (!ipv4_is_multicast(addr))
 		return -EINVAL;
 
-	rtnl_lock();
-
 	imr.imr_multiaddr.s_addr = msf->imsf_multiaddr;
 	imr.imr_address.s_addr = msf->imsf_interface;
 	imr.imr_ifindex = 0;
@@ -2417,7 +2417,6 @@ int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
 		goto done;
 	msf->imsf_fmode = pmc->sfmode;
 	psl = rtnl_dereference(pmc->sflist);
-	rtnl_unlock();
 	if (!psl) {
 		len = 0;
 		count = 0;
@@ -2436,7 +2435,6 @@ int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
 		return -EFAULT;
 	return 0;
 done:
-	rtnl_unlock();
 	return err;
 }
 
@@ -2450,6 +2448,8 @@ int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
 	struct inet_sock *inet = inet_sk(sk);
 	struct ip_sf_socklist *psl;
 
+	ASSERT_RTNL();
+
 	psin = (struct sockaddr_in *)&gsf->gf_group;
 	if (psin->sin_family != AF_INET)
 		return -EINVAL;
@@ -2457,8 +2457,6 @@ int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
 	if (!ipv4_is_multicast(addr))
 		return -EINVAL;
 
-	rtnl_lock();
-
 	err = -EADDRNOTAVAIL;
 
 	for_each_pmc_rtnl(inet, pmc) {
@@ -2470,7 +2468,6 @@ int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
 		goto done;
 	gsf->gf_fmode = pmc->sfmode;
 	psl = rtnl_dereference(pmc->sflist);
-	rtnl_unlock();
 	count = psl ? psl->sl_count : 0;
 	copycount = count < gsf->gf_numsrc ? count : gsf->gf_numsrc;
 	gsf->gf_numsrc = count;
@@ -2490,7 +2487,6 @@ int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
 	}
 	return 0;
 done:
-	rtnl_unlock();
 	return err;
 }