mld: respect RCU rules in ip6_mc_source() and ip6_mc_msfilter()

Whenever RCU protected list replaces an object,
the pointer to the new object needs to be updated
_before_ the call to kfree_rcu() or call_rcu()

Also ip6_mc_msfilter() needs to update the pointer
before releasing the mc_lock mutex.

Note that linux-5.13 was supporting kfree_rcu(NULL, rcu),
so this fix does not need the conditional test I was
forced to use in the equivalent patch for IPv4.

Fixes: a2790dc6a8a6 ("mld: convert ipv6_mc_socklist->sflist to RCU")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 909f937befd71fce194517d44cb9a4c5e2876360..7f695c39d9a8c4410e619b88add23e39f2beabae 100644 (file)
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -460,10 +460,10 @@ int ip6_mc_source(int add, int omode, struct sock *sk,
                                newpsl->sl_addr[i] = psl->sl_addr[i];
                        atomic_sub(struct_size(psl, sl_addr, psl->sl_max),
                                   &sk->sk_omem_alloc);
-                       kfree_rcu(psl, rcu);
                }
+               rcu_assign_pointer(pmc->sflist, newpsl);
+               kfree_rcu(psl, rcu);
                psl = newpsl;
-               rcu_assign_pointer(pmc->sflist, psl);
        }
        rv = 1; /* > 0 for insert logic below if sl_count is 0 */
        for (i = 0; i < psl->sl_count; i++) {
@@ -565,12 +565,12 @@ int ip6_mc_msfilter(struct sock *sk, struct group_filter *gsf,
                               psl->sl_count, psl->sl_addr, 0);
                atomic_sub(struct_size(psl, sl_addr, psl->sl_max),
                           &sk->sk_omem_alloc);
-               kfree_rcu(psl, rcu);
        } else {
                ip6_mc_del_src(idev, group, pmc->sfmode, 0, NULL, 0);
        }
-       mutex_unlock(&idev->mc_lock);
        rcu_assign_pointer(pmc->sflist, newpsl);
+       mutex_unlock(&idev->mc_lock);
+       kfree_rcu(psl, rcu);
        pmc->sfmode = gsf->gf_fmode;
        err = 0;
 done: