Re: net: lockdep warning in ip_mc_msfget (net/ipv4/igmp.c:2400)

[Cong Wang]

On Mon, Nov 2, 2015 at 1:31 PM, Cong Wang <cwang@xxxxxxxxxxxxxxxx> wrote:
>
> Good catch!
>
> This is probably introduced by:
>
> commit baf606d9c9b12517e47e0d1370e8aa9f7323f210
> Author: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> Date:   Wed Mar 18 14:50:42 2015 -0300
>
>     ipv4,ipv6: grab rtnl before locking the socket
>
> I am thinking what is the right way to fix it...

Please try the attached patch.

Thanks!
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index d38b8b6..a2429b7 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;
 }
 
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index c3c359a..2b12ed2 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -1251,11 +1251,22 @@ EXPORT_SYMBOL(compat_ip_setsockopt);
  *	the _received_ ones. The set sets the _sent_ ones.
  */
 
+static bool getsockopt_needs_rtnl(int optname)
+{
+	switch (optname) {
+	case IP_MSFILTER:
+	case MCAST_MSFILTER:
+		return true;
+	}
+	return false;
+}
+
 static int do_ip_getsockopt(struct sock *sk, int level, int optname,
 			    char __user *optval, int __user *optlen, unsigned int flags)
 {
 	struct inet_sock *inet = inet_sk(sk);
-	int val;
+	bool needs_rtnl = getsockopt_needs_rtnl(optname);
+	int val, err;
 	int len;
 
 	if (level != SOL_IP)
@@ -1269,6 +1280,8 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
 	if (len < 0)
 		return -EINVAL;
 
+	if (needs_rtnl)
+		rtnl_lock();
 	lock_sock(sk);
 
 	switch (optname) {
@@ -1389,17 +1402,16 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
 		int err;
 
 		if (len < IP_MSFILTER_SIZE(0)) {
-			release_sock(sk);
-			return -EINVAL;
+			err = -EINVAL;
+			goto out;
 		}
 		if (copy_from_user(&msf, optval, IP_MSFILTER_SIZE(0))) {
-			release_sock(sk);
-			return -EFAULT;
+			err = -EFAULT;
+			goto out;
 		}
 		err = ip_mc_msfget(sk, &msf,
 				   (struct ip_msfilter __user *)optval, optlen);
-		release_sock(sk);
-		return err;
+		goto out;
 	}
 	case MCAST_MSFILTER:
 	{
@@ -1407,18 +1419,17 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
 		int err;
 
 		if (len < GROUP_FILTER_SIZE(0)) {
-			release_sock(sk);
-			return -EINVAL;
+			err = -EINVAL;
+			goto out;
 		}
 		if (copy_from_user(&gsf, optval, GROUP_FILTER_SIZE(0))) {
-			release_sock(sk);
-			return -EFAULT;
+			err = -EFAULT;
+			goto out;
 		}
 		err = ip_mc_gsfget(sk, &gsf,
 				   (struct group_filter __user *)optval,
 				   optlen);
-		release_sock(sk);
-		return err;
+		goto out;
 	}
 	case IP_MULTICAST_ALL:
 		val = inet->mc_all;
@@ -1485,6 +1496,12 @@ static int do_ip_getsockopt(struct sock *sk, int level, int optname,
 			return -EFAULT;
 	}
 	return 0;
+
+out:
+	release_sock(sk);
+	if (needs_rtnl)
+		rtnl_unlock();
+	return err;
 }
 
 int ip_getsockopt(struct sock *sk, int level,