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Re: kern/54150: COMPAT_50 vs NET_RT_IFLIST
The following reply was made to PR kern/54150; it has been noted by GNATS.
From: Robert Elz <kre%munnari.OZ.AU@localhost>
Subject: Re: kern/54150: COMPAT_50 vs NET_RT_IFLIST
Date: Fri, 03 May 2019 02:48:00 +0700
I think I understand what might be happening here now.
getifaddrs() uses sysctl(net.route.0.0.iflist.0)
That sysctl returns a list of message structures, when we are
running compatible userland/kernel there will be a sequence of
RTM_IFINFO ad RTM_NEWADDR messages.
When userland is NetBSD 5, the RTM_IFINFO is replaced by RTM_OOIFINFO
(which is generated by compat_50_iflist) and RTM_ONEWADDR (which is
generated by compat_70_iflist_addr)
It is compat_70_iflist_addr as this structure had not changed between
netbsd 5 and netbsd 7 (the change between netbsd 7 and 8 was the first
change of that struct)
Of itself, all that is OK. However, there is another change. Each
message is preceded by a header, which starts with a length, type,
and version. The length and type are handled by the code above.
Unfortunately, RTM_VERSION altered between NetBSD 5 and NetBSD 7,
compat_50_iflist() generates a message rith RTM_OVERSION (3) in it, and
compat_70_iflist_addr() generates a message with RTM_VERSION (4).
Those are the appropriate values for NetBSD 5 and 7 resp.
But both of those end up appearing in the same sysctl result.
getifaddrs() (all versions - or at least, the NetBSD 5 and later ones,
which is all Ihave looked at) checks that the version field is
RTM_VERSION (whichever version is appropriate for the version of
getifaddrs() in use) and ignores anything that is not.
The NEWADDR messages, which appear as RTMVersion 4 all get ignored by
a NetBSD 5 getifaddrs(), and those are what contain the interface names
I suspect that what we need is to make a compat_50_iflist_addr()
function, identical to compat_70_iflist_addr() except using RTM_OVERSION
instead of RTM_VERSION (the two could use some common routine to fill in
all the rest of the details). However, I have not yet tried it.
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