netdev - Re: sockets affected by IPsec always block (2.6.23)

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Message-Id: <20071204.231200.117152338.davem@davemloft.net>
Date:	Tue, 04 Dec 2007 23:12:00 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	simon@...e.lp0.eu, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: sockets affected by IPsec always block (2.6.23)

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Wed, 5 Dec 2007 17:51:32 +1100

> Does anybody actually need the 0 setting? What would we break if
> the default became 1?

I bet there are UDP apps out there that would break if we
didn't do this.

Actually, consider even a case like DNS.  Let's say the timeout
is set to 2 seconds or something and you have 3 DNS servers
listed, on different IPSEC destinations, in your resolv.conf

Each IPSEC route that isn't currently resolved will cause packet loss
of the DNS lookup request with xfrm_larval_drop set to '1'.

If all 3 need to be resolved, the DNS lookup will fully fail
which defeats the purpose of listing 3 servers for redundancy
don't you think? :-)

As much as I even personally prefer the xfrm_larval_drop=1
behavior, it cases like above that keep me from jumping at
making it the default.

Arguably, potentially blocking forever (which is what can easily
happen with xfrm_larval_drop=0 if your IPSEC daemon cannot resolve the
IPSEC path for whatever reason) is worse than the above, but the
other cases are still something to consider as well.
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