ipv6: kill sk_dst_lock

While testing the np->opt RCU conversion, I found that UDP/IPv6 was
using a mixture of xchg() and sk_dst_lock to protect concurrent changes
to sk->sk_dst_cache, leading to possible corruptions and crashes.

ip6_sk_dst_lookup_flow() uses sk_dst_check() anyway, so the simplest
way to fix the mess is to remove sk_dst_lock completely, as we did for
IPv4.

__ip6_dst_store() and ip6_dst_store() share same implementation.

sk_setup_caps() being called with socket lock being held or not,
we have to use sk_dst_set() instead of __sk_dst_set()

Note that I had to move the "np->dst_cookie = rt6_get_cookie(rt);"
in ip6_dst_store() before the sk_setup_caps(sk, dst) call.

This is because ip6_dst_store() can be called from process context,
without any lock held.

As soon as the dst is installed in sk->sk_dst_cache, dst can be freed
from another cpu doing a concurrent ip6_dst_store()

Doing the dst dereference before doing the install is needed to make
sure no use after free would trigger.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 9 deletions

diff --git a/net/ipv6/inet6_connection_sock.c b/net/ipv6/inet6_connection_sock.c
index 3ff5208772bb..a7ca2cde2ecb 100644
--- a/net/ipv6/inet6_connection_sock.c
+++ b/net/ipv6/inet6_connection_sock.c
@@ -111,14 +111,6 @@ void inet6_csk_addr2sockaddr(struct sock *sk, struct sockaddr *uaddr)
 EXPORT_SYMBOL_GPL(inet6_csk_addr2sockaddr);
 
 static inline
-void __inet6_csk_dst_store(struct sock *sk, struct dst_entry *dst,
-			   const struct in6_addr *daddr,
-			   const struct in6_addr *saddr)
-{
-	__ip6_dst_store(sk, dst, daddr, saddr);
-}
-
-static inline
 struct dst_entry *__inet6_csk_dst_check(struct sock *sk, u32 cookie)
 {
 	return __sk_dst_check(sk, cookie);
@@ -153,7 +145,7 @@ static struct dst_entry *inet6_csk_route_socket(struct sock *sk,
 		dst = ip6_dst_lookup_flow(sk, fl6, final_p);
 
 		if (!IS_ERR(dst))
-			__inet6_csk_dst_store(sk, dst, NULL, NULL);
+			ip6_dst_store(sk, dst, NULL, NULL);
 	}
 	return dst;
 }