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ipv6: mcast: use rcu_assign_pointer() for __rcu list updates

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Several places in net/ipv6/mcast.c update RCU-protected lists
(np->ipv6_mc_list, idev->mc_list, idev->mc_tomb) using direct pointer
assignments instead of rcu_assign_pointer():

1. In __ipv6_dev_mc_dec(), unlinking a group from idev->mc_list did:
       *map = ma->next;
   without rcu_assign_pointer() while concurrent readers traverse
   idev->mc_list locklessly under rcu_read_lock().
2. In ipv6_sock_mc_drop() and __ipv6_sock_mc_close(), unlinking a group
   from np->ipv6_mc_list directly assigned *lnk = mc_lst->next and
   np->ipv6_mc_list = mc_lst->next without rcu_assign_pointer(), racing
   with lockless readers in inet6_mc_check().
3. In __ipv6_sock_mc_join(), mc_lst->next was initialized to
   np->ipv6_mc_list via raw assignment before publishing mc_lst.
4. In mld_del_delrec() and __ipv6_dev_mc_inc(), __rcu source pointers
   passed into rcu_assign_pointer() lacked explicit dereference helpers.

Fix these by consistently using rcu_assign_pointer() along with
mc_dereference() / sock_dereference().

Fixes: 456b61bca8 ("ipv6: mcast: RCU conversion")
Fixes: 88e2ca3080 ("mld: convert ifmcaddr6 to RCU")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Taehee Yoo <ap420073@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20260828084531.1826790-5-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2026-08-28 08:45:30 +00:00 committed by Jakub Kicinski
parent 75fa9caeb8
commit 0c8f56c583
1 changed files with 13 additions and 7 deletions
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20
net/ipv6/mcast.c
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@ -240,7 +240,8 @@ static int __ipv6_sock_mc_join(struct sock *sk, int ifindex,
return err;
}
mc_lst->next = np->ipv6_mc_list;
rcu_assign_pointer(mc_lst->next,
sock_dereference(np->ipv6_mc_list, sk));
rcu_assign_pointer(np->ipv6_mc_list, mc_lst);
return 0;
@ -300,7 +301,8 @@ int ipv6_sock_mc_drop(struct sock *sk, int ifindex, const struct in6_addr *addr)
lnk = &mc_lst->next) {
if ((ifindex == 0 || mc_lst->ifindex == ifindex) &&
ipv6_addr_equal(&mc_lst->addr, addr)) {
*lnk = mc_lst->next;
rcu_assign_pointer(*lnk,
sock_dereference(mc_lst->next, sk));
__ipv6_sock_mc_drop(sk, mc_lst);
return 0;
}
@ -333,7 +335,8 @@ void __ipv6_sock_mc_close(struct sock *sk)
struct ipv6_mc_socklist *mc_lst;
while ((mc_lst = sock_dereference(np->ipv6_mc_list, sk)) != NULL) {
np->ipv6_mc_list = mc_lst->next;
rcu_assign_pointer(np->ipv6_mc_list,
sock_dereference(mc_lst->next, sk));
__ipv6_sock_mc_drop(sk, mc_lst);
}
}
@ -798,9 +801,11 @@ static void mld_del_delrec(struct inet6_dev *idev, struct ifmcaddr6 *im)
if (!pmc)
return;
if (pmc_prev)
rcu_assign_pointer(pmc_prev->next, pmc->next);
rcu_assign_pointer(pmc_prev->next,
mc_dereference(pmc->next, idev));
else
rcu_assign_pointer(idev->mc_tomb, pmc->next);
rcu_assign_pointer(idev->mc_tomb,
mc_dereference(pmc->next, idev));
im->idev = pmc->idev;
if (im->mca_sfmode == MCAST_INCLUDE) {
@ -980,7 +985,7 @@ static int __ipv6_dev_mc_inc(struct net_device *dev,
return -ENOMEM;
}
rcu_assign_pointer(mc->next, idev->mc_list);
rcu_assign_pointer(mc->next, mc_dereference(idev->mc_list, idev));
rcu_assign_pointer(idev->mc_list, mc);
mld_del_delrec(idev, mc);
@ -1014,7 +1019,8 @@ int __ipv6_dev_mc_dec(struct inet6_dev *idev, const struct in6_addr *addr)
WRITE_ONCE(ma->mca_users, new_users);
if (new_users == 0) {
*map = ma->next;
rcu_assign_pointer(*map,
mc_dereference(ma->next, idev));
igmp6_group_dropped(ma);
inet6_ifmcaddr_notify(idev->dev, ma,