On 6/6/23 16:11, Guillaume Nault wrote:
On Tue, Jun 06, 2023 at 03:57:35PM +0200, Mirsad Todorovac wrote:
diff --git a/net/ipv6/ping.c b/net/ipv6/ping.c index c4835dbdfcff..c1d81c49b775 100644 --- a/net/ipv6/ping.c +++ b/net/ipv6/ping.c @@ -73,6 +73,10 @@ static int ping_v6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) struct rt6_info *rt; struct pingfakehdr pfh; struct ipcm6_cookie ipc6;
struct net *net = sock_net(sk);
struct net_device *dev = NULL;
struct net_device *mdev = NULL;
struct net_device *bdev = NULL; err = ping_common_sendmsg(AF_INET6, msg, len, &user_icmph, sizeof(user_icmph));
@@ -111,10 +115,26 @@ static int ping_v6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) else if (!oif) oif = np->ucast_oif;
if (oif) {
rcu_read_lock();
dev = dev_get_by_index_rcu(net, oif);
rcu_read_unlock();
You can't assume '*dev' is still valid after rcu_read_unlock() unless you hold a reference on it.
rtnl_lock();
mdev = netdev_master_upper_dev_get(dev);
rtnl_unlock();
Because of that, 'dev' might have already disappeared at the time netdev_master_upper_dev_get() is called. So it may dereference an invalid pointer here.
Good point, thanks. I didn't expect those to change.
This can be fixed, provided that RCU and RTNL locks can be nested:
rcu_read_lock(); if (oif) { dev = dev_get_by_index_rcu(net, oif); rtnl_lock(); mdev = netdev_master_upper_dev_get(dev); rtnl_unlock(); }
if (sk->sk_bound_dev_if) { bdev = dev_get_by_index_rcu(net, sk->sk_bound_dev_if); }
addr_type = ipv6_addr_type(daddr); if ((__ipv6_addr_needs_scope_id(addr_type) && !oif) || (addr_type & IPV6_ADDR_MAPPED) || (oif && sk->sk_bound_dev_if && oif != sk->sk_bound_dev_if && !(mdev && sk->sk_bound_dev_if && bdev && mdev == bdev))) { rcu_read_unlock(); return -EINVAL; } rcu_read_unlock();
But again this is still probably not race-free (bdev might also disappear before the mdev == bdev test), even if it passed fcnal-test.sh, there is much duplication of code, so your one-line solution is obviously by far better. :-)
Much obliged.
Best regards, Mirsad
}
if (sk->sk_bound_dev_if) {
rcu_read_lock();
bdev = dev_get_by_index_rcu(net, sk->sk_bound_dev_if);
rcu_read_unlock();
}
addr_type = ipv6_addr_type(daddr); if ((__ipv6_addr_needs_scope_id(addr_type) && !oif) || (addr_type & IPV6_ADDR_MAPPED) ||
(oif && sk->sk_bound_dev_if && oif != sk->sk_bound_dev_if))
(oif && sk->sk_bound_dev_if && oif != sk->sk_bound_dev_if &&
!(mdev && sk->sk_bound_dev_if && bdev && mdev == bdev))) return -EINVAL; ipcm6_init_sk(&ipc6, np);
However, this works by the test (888 passed) but your two liner is obviously better :-)
:)