[PATCH 3.15 046/109] ipv4: irq safe sk_dst_[re]set() and ipv4_sk_update_pmtu() fix

Greg Kroah-Hartman
2014-07-26T19:23:24Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 7f502361531e9eecb396cf99bdc9e9a59f7ebd7f ]

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 commit e47eb5dfb296b ("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: 9cb3a50c5f63e ("ipv4: Invalidate the socket cached route on pmtu events if possible")
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/sock.h | 12 ++++++------
net/ipv4/route.c | 15 ++++++++-------
2 files changed, 14 insertions(+), 13 deletions(-)

--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1766,9 +1766,11 @@ __sk_dst_set(struct sock *sk, struct dst
static inline void
sk_dst_set(struct sock *sk, struct dst_entry *dst)
{
- spin_lock(&sk->sk_dst_lock);
- __sk_dst_set(sk, dst);
- spin_unlock(&sk->sk_dst_lock);
+ struct dst_entry *old_dst;
+
+ sk_tx_queue_clear(sk);
+ old_dst = xchg(&sk->sk_dst_cache, dst);
+ dst_release(old_dst);
}

static inline void
@@ -1780,9 +1782,7 @@ __sk_dst_reset(struct sock *sk)
static inline void
sk_dst_reset(struct sock *sk)
{
- spin_lock(&sk->sk_dst_lock);
- __sk_dst_reset(sk);
- spin_unlock(&sk->sk_dst_lock);
+ sk_dst_set(sk, NULL);
}

struct dst_entry *__sk_dst_check(struct sock *sk, u32 cookie);
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1022,7 +1022,7 @@ void ipv4_sk_update_pmtu(struct sk_buff
const struct iphdr *iph = (const struct iphdr *) skb->data;
struct flowi4 fl4;
struct rtable *rt;
- struct dst_entry *dst;
+ struct dst_entry *odst = NULL;
bool new = false;

bh_lock_sock(sk);
@@ -1030,16 +1030,17 @@ void ipv4_sk_update_pmtu(struct sk_buff
if (!ip_sk_accept_pmtu(sk))
goto out;

- rt = (struct rtable *) __sk_dst_get(sk);
+ odst = sk_dst_get(sk);

- if (sock_owned_by_user(sk) || !rt) {
+ if (sock_owned_by_user(sk) || !odst) {
__ipv4_sk_update_pmtu(skb, sk, mtu);
goto out;
}

__build_flow_key(&fl4, sk, iph, 0, 0, 0, 0, 0);

- if (!__sk_dst_check(sk, 0)) {
+ rt = (struct rtable *)odst;
+ if (odst->obsolete && odst->ops->check(odst, 0) == NULL) {
rt = ip_route_output_flow(sock_net(sk), &fl4, sk);
if (IS_ERR(rt))
goto out;
@@ -1049,8 +1050,7 @@ void ipv4_sk_update_pmtu(struct sk_buff

__ip_rt_update_pmtu((struct rtable *) rt->dst.path, &fl4, mtu);

- dst = dst_check(&rt->dst, 0);
- if (!dst) {
+ if (!dst_check(&rt->dst, 0)) {
if (new)
dst_release(&rt->dst);

@@ -1062,10 +1062,11 @@ void ipv4_sk_update_pmtu(struct sk_buff
}

if (new)
- __sk_dst_set(sk, &rt->dst);
+ sk_dst_set(sk, &rt->dst);

out:
bh_unlock_sock(sk);
+ dst_release(odst);
}
EXPORT_SYMBOL_GPL(ipv4_sk_update_pmtu);