On 03/23/2018 07:39 AM, Alexey Kodanev wrote:
> After commit 33c162a980fe ("ipv6: datagram: Update dst cache of a
> connected datagram sk during pmtu update"), when the error occurs on
> sending datagram in udpv6_sendmsg() due to ICMPV6_PKT_TOOBIG type,
> error handler can trigger the following path and call ip6_dst_store():
>
> udpv6_err()
> ip6_sk_update_pmtu()
> ip6_datagram_dst_update()
> ip6_dst_lookup_flow(), can create a RTF_CACHE clone
> ...
> ip6_dst_store()
>
> It can happen before a connected UDP socket invokes ip6_dst_store()
> in the end of udpv6_sendmsg(), on destination release, as a result,
> the last one changes dst to the old one, preventing getting updated
> dst cache on the next udpv6_sendmsg() call.
>
> This patch moves ip6_dst_store() in udpv6_sendmsg(), so that it is
> invoked after ip6_sk_dst_lookup_flow() and before udp_v6_send_skb().
>
A Fixes: tag would be nice, for automatic tools (and humans as well)
> Signed-off-by: Alexey Kodanev <alexey.koda...@oracle.com>
> ---
> net/ipv6/udp.c | 22 +++++++++++-----------
> 1 file changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> index 52e3ea0..0d413c6 100644
> --- a/net/ipv6/udp.c
> +++ b/net/ipv6/udp.c
> @@ -1299,6 +1299,16 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg,
> size_t len)
> if (ipc6.hlimit < 0)
> ipc6.hlimit = ip6_sk_dst_hoplimit(np, &fl6, dst);
>
> + if (connected)
> + ip6_dst_store(sk, dst,
> + ipv6_addr_equal(&fl6.daddr, &sk->sk_v6_daddr) ?
> + &sk->sk_v6_daddr : NULL,
> +#ifdef CONFIG_IPV6_SUBTREES
> + ipv6_addr_equal(&fl6.saddr, &np->saddr) ?
> + &np->saddr :
> +#endif
> + NULL);
> +
What about the MSG_CONFIRM stuff ?
> if (msg->msg_flags&MSG_CONFIRM)
> goto do_confirm;
> back_from_confirm:
Should not you move the above code here instead ?
Also ip6_dst_store() does not increment dst refcount.
I fear that as soon as dst is visible to other cpus, it might be stolen.
> @@ -1350,18 +1360,8 @@ int udpv6_sendmsg(struct sock *sk, struct msghdr *msg,
> size_t len)
>
> release_dst:
> if (dst) {
> - if (connected) {
> - ip6_dst_store(sk, dst,
> - ipv6_addr_equal(&fl6.daddr,
> &sk->sk_v6_daddr) ?
> - &sk->sk_v6_daddr : NULL,
> -#ifdef CONFIG_IPV6_SUBTREES
> - ipv6_addr_equal(&fl6.saddr, &np->saddr) ?
> - &np->saddr :
> -#endif
> - NULL);
> - } else {
> + if (!connected)
> dst_release(dst);
> - }
> dst = NULL;
> }
>
>
