When IPV6_MROUTE_MULTIPLE_TABLES is enabled, multicast routing tables
must be read under RCU or RTNL lock.

Detected by Lockdep-RCU:

  [   48.834645] WARNING: suspicious RCU usage
  [   48.834647] 6.1.103-584209f6d5-nokia_sm_x86 #1 Tainted: G S         O
  [   48.834649] -----------------------------
  [   48.834651] /net/ipv6/ip6mr.c:132 RCU-list traversed in non-reader section!!
  [   48.834654]
                 other info that might help us debug this:

  [   48.834656]
                 rcu_scheduler_active = 2, debug_locks = 1
  [   48.834658] no locks held by radvd/5777.
  [   48.834660]
                 stack backtrace:
  [   48.834663] CPU: 0 PID: 5777 Comm: radvd Tainted: G S         O       6.1.103-584209f6d5-nokia_sm_x86 #1
  [   48.834666] Hardware name: Nokia Asil/Default string, BIOS 0ACNA113 06/07/2024
  [   48.834673] Call Trace:
  [   48.834674]  <TASK>
  [   48.834677]  dump_stack_lvl+0xb7/0xe9
  [   48.834687]  lockdep_rcu_suspicious.cold+0x2d/0x64
  [   48.834697]  ip6mr_get_table+0x9f/0xb0
  [   48.834704]  ip6mr_ioctl+0x50/0x360
  [   48.834713]  ? sk_ioctl+0x5f/0x1c0
  [   48.834719]  sk_ioctl+0x5f/0x1c0
  [   48.834723]  ? find_held_lock+0x2b/0x80
  [   48.834731]  sock_do_ioctl+0x7b/0x140
  [   48.834737]  ? proc_nr_files+0x30/0x30
  [   48.834744]  sock_ioctl+0x1f5/0x360
  [   48.834754]  __x64_sys_ioctl+0x8d/0xd0
  [   48.834760]  do_syscall_64+0x3c/0x90
  [   48.834765]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
                  ...
  [   48.834802]  </TASK>

Signed-off-by: Stefan Wiehler <stefan.wiehler@nokia.com>
Fixes: d1db275dd3f6 ("ipv6: ip6mr: support multiple tables")
---
 net/ipv6/ip6mr.c | 39 ++++++++++++++++++++++++---------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 3acc4c8a226d..19ce010016b9 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -1887,47 +1887,56 @@ int ip6mr_ioctl(struct sock *sk, int cmd, void *arg)
 	struct mfc6_cache *c;
 	struct net *net = sock_net(sk);
 	struct mr_table *mrt;
+	int err;
 
+	rcu_read_lock();
 	mrt = ip6mr_get_table(net, raw6_sk(sk)->ip6mr_table ? : RT6_TABLE_DFLT);
-	if (!mrt)
-		return -ENOENT;
+	if (!mrt) {
+		err = -ENOENT;
+		goto out;
+	}
 
 	switch (cmd) {
 	case SIOCGETMIFCNT_IN6:
 		vr = (struct sioc_mif_req6 *)arg;
-		if (vr->mifi >= mrt->maxvif)
-			return -EINVAL;
+		if (vr->mifi >= mrt->maxvif) {
+			err = -EINVAL;
+			goto out;
+		}
 		vr->mifi = array_index_nospec(vr->mifi, mrt->maxvif);
-		rcu_read_lock();
 		vif = &mrt->vif_table[vr->mifi];
 		if (VIF_EXISTS(mrt, vr->mifi)) {
 			vr->icount = READ_ONCE(vif->pkt_in);
 			vr->ocount = READ_ONCE(vif->pkt_out);
 			vr->ibytes = READ_ONCE(vif->bytes_in);
 			vr->obytes = READ_ONCE(vif->bytes_out);
-			rcu_read_unlock();
-			return 0;
+			err = 0;
+			goto out;
 		}
-		rcu_read_unlock();
-		return -EADDRNOTAVAIL;
+		err = -EADDRNOTAVAIL;
+		goto out;
 	case SIOCGETSGCNT_IN6:
 		sr = (struct sioc_sg_req6 *)arg;
 
-		rcu_read_lock();
 		c = ip6mr_cache_find(mrt, &sr->src.sin6_addr,
 				     &sr->grp.sin6_addr);
 		if (c) {
 			sr->pktcnt = c->_c.mfc_un.res.pkt;
 			sr->bytecnt = c->_c.mfc_un.res.bytes;
 			sr->wrong_if = c->_c.mfc_un.res.wrong_if;
-			rcu_read_unlock();
-			return 0;
+			err = 0;
+			goto out;
 		}
-		rcu_read_unlock();
-		return -EADDRNOTAVAIL;
+		err = -EADDRNOTAVAIL;
+		goto out;
 	default:
-		return -ENOIOCTLCMD;
+		err = -ENOIOCTLCMD;
+		goto out;
 	}
+
+out:
+	rcu_read_unlock();
+	return err;
 }
 
 #ifdef CONFIG_COMPAT
-- 
2.42.0