netdev - Re: [PATCH] ipv6: Fix the pmtu path for connected UDP socket

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Message-ID: <20160307212815.GA5613@kafai-mba.gkf168.com>
Date:	Mon, 7 Mar 2016 13:28:15 -0800
From:	Martin KaFai Lau <kafai@...com>
To:	Wei Wang <weiwan@...gle.com>
CC:	"David S . Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH] ipv6: Fix the pmtu path for connected UDP socket

On Wed, Mar 02, 2016 at 11:19:21AM -0800, Wei Wang wrote:
> From: Wei Wang <weiwan@...gle.com>
>
> When ICMPV6_PKT_TOOBIG message is received by a connected UDP socket,
> the new mtu value is not properly updated in the dst_entry associated
> with the socket.
> This leads to the issue that the mtu value returned by getsockopt(sockfd,
> IPPROTO_IPV6, IPV6_MTU, ...) is wrong.
> The fix is to call the corresponding pmtu related function for connected
> socket so that the dst_entry associated with the socket will get updated
> with the new mtu value.
Would it be a better fix if ip6_sk_update_pmtu() does a dst_check() and
updates sk->sk_dst_cache (if needed) before it returns?  It seems
ipv4_sk_update_pmtu() is also doing it.

or

sk->sk_dst_cache is still valid after ip6_sk_update_pmtu() returns?