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ipv6: mcast: Check inet6_dev->dead under idev->mc_lock in __ipv6_dev_mc_inc().
Since commit 63ed8de4be
("mld: add mc_lock for protecting
per-interface mld data"), every multicast resource is protected
by inet6_dev->mc_lock.
RTNL is unnecessary in terms of protection but still needed for
synchronisation between addrconf_ifdown() and __ipv6_dev_mc_inc().
Once we removed RTNL, there would be a race below, where we could
add a multicast address to a dead inet6_dev.
CPU1 CPU2
==== ====
addrconf_ifdown() __ipv6_dev_mc_inc()
if (idev->dead) <-- false
dead = true return -ENODEV;
ipv6_mc_destroy_dev() / ipv6_mc_down()
mutex_lock(&idev->mc_lock)
...
mutex_unlock(&idev->mc_lock)
mutex_lock(&idev->mc_lock)
...
mutex_unlock(&idev->mc_lock)
The race window can be easily closed by checking inet6_dev->dead
under inet6_dev->mc_lock in __ipv6_dev_mc_inc() as addrconf_ifdown()
will acquire it after marking inet6_dev dead.
Let's check inet6_dev->dead under mc_lock in __ipv6_dev_mc_inc().
Note that now __ipv6_dev_mc_inc() no longer depends on RTNL and
we can remove ASSERT_RTNL() there and the RTNL comment above
addrconf_join_solict().
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250702230210.3115355-4-kuni1840@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
parent
818ae1a5ec
commit
dbd40f318c
@ -2229,13 +2229,12 @@ errdad:
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in6_ifa_put(ifp);
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}
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/* Join to solicited addr multicast group.
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* caller must hold RTNL */
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/* Join to solicited addr multicast group. */
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void addrconf_join_solict(struct net_device *dev, const struct in6_addr *addr)
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{
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struct in6_addr maddr;
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if (dev->flags&(IFF_LOOPBACK|IFF_NOARP))
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if (READ_ONCE(dev->flags) & (IFF_LOOPBACK | IFF_NOARP))
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return;
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addrconf_addr_solict_mult(addr, &maddr);
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@ -3865,7 +3864,7 @@ static int addrconf_ifdown(struct net_device *dev, bool unregister)
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* Do not dev_put!
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*/
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if (unregister) {
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idev->dead = 1;
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WRITE_ONCE(idev->dead, 1);
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/* protected by rtnl_lock */
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RCU_INIT_POINTER(dev->ip6_ptr, NULL);
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@ -952,23 +952,22 @@ error:
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static int __ipv6_dev_mc_inc(struct net_device *dev,
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const struct in6_addr *addr, unsigned int mode)
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{
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struct ifmcaddr6 *mc;
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struct inet6_dev *idev;
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ASSERT_RTNL();
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struct ifmcaddr6 *mc;
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/* we need to take a reference on idev */
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idev = in6_dev_get(dev);
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if (!idev)
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return -EINVAL;
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if (idev->dead) {
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mutex_lock(&idev->mc_lock);
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if (READ_ONCE(idev->dead)) {
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mutex_unlock(&idev->mc_lock);
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in6_dev_put(idev);
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return -ENODEV;
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}
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mutex_lock(&idev->mc_lock);
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for_each_mc_mclock(idev, mc) {
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if (ipv6_addr_equal(&mc->mca_addr, addr)) {
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mc->mca_users++;
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