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ipv4: irq safe sk_dst_[re]set() and ipv4_sk_update_pmtu() fix
We have two different ways to handle changes to sk->sk_dst First way (used by TCP) assumes socket lock is owned by caller, and use no extra lock : __sk_dst_set() & __sk_dst_reset() Another way (used by UDP) uses sk_dst_lock because socket lock is not always taken. Note that sk_dst_lock is not softirq safe. These ways are not inter changeable for a given socket type. ipv4_sk_update_pmtu(), added in linux-3.8, added a race, as it used the socket lock as synchronization, but users might be UDP sockets. Instead of converting sk_dst_lock to a softirq safe version, use xchg() as we did for sk_rx_dst in commite47eb5dfb2
("udp: ipv4: do not use sk_dst_lock from softirq context") In a follow up patch, we probably can remove sk_dst_lock, as it is only used in IPv6. Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Steffen Klassert <steffen.klassert@secunet.com> Fixes:9cb3a50c5f
("ipv4: Invalidate the socket cached route on pmtu events if possible") Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -1768,9 +1768,11 @@ __sk_dst_set(struct sock *sk, struct dst_entry *dst)
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static inline void
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sk_dst_set(struct sock *sk, struct dst_entry *dst)
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{
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spin_lock(&sk->sk_dst_lock);
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__sk_dst_set(sk, dst);
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spin_unlock(&sk->sk_dst_lock);
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struct dst_entry *old_dst;
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sk_tx_queue_clear(sk);
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old_dst = xchg(&sk->sk_dst_cache, dst);
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dst_release(old_dst);
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}
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static inline void
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@ -1782,9 +1784,7 @@ __sk_dst_reset(struct sock *sk)
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static inline void
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sk_dst_reset(struct sock *sk)
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{
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spin_lock(&sk->sk_dst_lock);
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__sk_dst_reset(sk);
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spin_unlock(&sk->sk_dst_lock);
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sk_dst_set(sk, NULL);
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}
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struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie);
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@ -1010,7 +1010,7 @@ void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
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const struct iphdr *iph = (const struct iphdr *) skb->data;
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struct flowi4 fl4;
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struct rtable *rt;
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struct dst_entry *dst;
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struct dst_entry *odst = NULL;
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bool new = false;
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bh_lock_sock(sk);
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@ -1018,16 +1018,17 @@ void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
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if (!ip_sk_accept_pmtu(sk))
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goto out;
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rt = (struct rtable *) __sk_dst_get(sk);
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odst = sk_dst_get(sk);
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if (sock_owned_by_user(sk) || !rt) {
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if (sock_owned_by_user(sk) || !odst) {
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__ipv4_sk_update_pmtu(skb, sk, mtu);
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goto out;
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}
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__build_flow_key(&fl4, sk, iph, 0, 0, 0, 0, 0);
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if (!__sk_dst_check(sk, 0)) {
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rt = (struct rtable *)odst;
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if (odst->obsolete && odst->ops->check(odst, 0) == NULL) {
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rt = ip_route_output_flow(sock_net(sk), &fl4, sk);
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if (IS_ERR(rt))
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goto out;
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@ -1037,8 +1038,7 @@ void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
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__ip_rt_update_pmtu((struct rtable *) rt->dst.path, &fl4, mtu);
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dst = dst_check(&rt->dst, 0);
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if (!dst) {
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if (!dst_check(&rt->dst, 0)) {
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if (new)
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dst_release(&rt->dst);
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@ -1050,10 +1050,11 @@ void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
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}
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if (new)
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__sk_dst_set(sk, &rt->dst);
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sk_dst_set(sk, &rt->dst);
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out:
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bh_unlock_sock(sk);
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dst_release(odst);
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}
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EXPORT_SYMBOL_GPL(ipv4_sk_update_pmtu);
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