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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 commit e47eb5dfb2 ("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>
This commit is contained in:
Eric Dumazet 2014-06-30 01:26:23 -07:00 committed by David S. Miller
parent dba63115ce
commit 7f50236153
2 changed files with 14 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
include/net/sock.h
View File

@ -1768,9 +1768,11 @@ __sk_dst_set(struct sock *sk, struct dst_entry *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
@ -1782,9 +1784,7 @@ __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);

15
net/ipv4/route.c
View File

@ -1010,7 +1010,7 @@ void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
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);
@ -1018,16 +1018,17 @@ void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
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;
@ -1037,8 +1038,7 @@ void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
__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);
@ -1050,10 +1050,11 @@ void ipv4_sk_update_pmtu(struct sk_buff *skb, struct sock *sk, u32 mtu)
}
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);