Date: Thu, 01 Mar 2007 11:54:08 +0000 From: "Bruce M. Simpson" <bms@FreeBSD.org> To: net@FreeBSD.org Subject: Re: nconsistencies with IP_ONESBCAST and/or IP_SENDSRCADDR Message-ID: <45E6BEE0.2050307@FreeBSD.org> In-Reply-To: <45C0CA5D.5090903@incunabulum.net>
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Bruce M Simpson wrote: > Hello, > > In preparation for tightening up our handling of INADDR_BROADCAST > sends, I ran some brief tests today on the network stack with the > attached test code. > > I found some inconsistencies when run against 6.2-RELEASE; > > 1. IP_ONESBCAST breaks if SO_DONTROUTE is specified. > > One thing appears to be consistent about the failure mode: bad UDP > checksums. > dc(4) is being used on the destination end of the test network, so > checksum offloading should not be an issue. > I am also seeing the wrong destination address being used in most > cases. This is intermittent regardless of whether the socket is bound > or unbound. This is consistent with ip_output() treating its internal flag IP_SENDONES as separate from IP_ROUTETOIF. I was skimming an old patch of mine which attempts to implement part of SO_BINDTODEVICE which contains a fix related to this condition. The fix isn't the right fix so I will revisit this now and hopefully commit a fix shortly. > > 2. IP_SENDSRCADDR has some other inconsistencies. > a. The option is always rejected if the socket is not bound. > I find this behaviour suspect; the whole point of the option is to > specify, for SOCK_DGRAM and SOCK_RAW, the source address of a packet. > b. 0.0.0.0 is always accepted. > A regular interface lookup is used based on destination if this is > specified. This appears suspect to me because such an option is > redundant. This is of course a separate issue. Because it's more involved (it concerns the general concept of 'ip unnumbered' in the stack) it needs further consideration before any fix is attempted. udp_output() will only call in_pcbbind_setup() if a non-INADDR_ANY source address was specified; this is usually obtained from the socket being bound previously. This explains why the IP_SENDSRCADDR option is rejected in udp_output() for an unbound socket. It *will* be accepted if the option contains INADDR_ANY. In this case, normal source address selection takes place. This is a good use case demonstrating the need for source address selection logic such as is now found in NetBSD. There is no sanity checking on the IP_SENDSRCADDR option data containing INADDR_ANY; such an option is redundant and is nonsensical for an unbound socket. We should reject the option if it contains INADDR_ANY if and only if the socket is not bound. Implementing such a check is fairly easy and makes sense for this use case. Returning EINVAL in this case seems acceptable according to ip(4). The option *should* be accepted if the application has bound the socket to a device somehow (oh dear, SO_BINDTODEVICE rears its head again) as DHCP for example needs to override any IPv4 address which may be assigned on an ifnet with 0.0.0.0. Regards, BMShome | help
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