Bug#65041: glibc does not allow numeric hostnames
It seems to me that gotom's analysis is correct: gethostbyname
interprets an all-numeric-no-dots argument string as an IP address; see
(libc.info.gz)Abstract Host Addresses for details. What this ultimately
means is that gethostbyname cannot resolve an all-numeric hostname into
a fully qualified domain name, since it never does the name lookup if it
detects an all-numeric IP address.
It is arguable that the formats of IP addresses that gethostbyname
supports are rare enough that they don't matter and we could rip out
support for them. However, it is also arguable that an all-numeric
hostname is rare enough that there is no point in breaking things that
use the rare formats just so hostnames can be all-digits.
We can't support both all-numeric hostnames and the no-dots notation for
an IP address at the same time. The gethostbyname interface does not
allow us to choose on a case by case basis which we prefer. Therefore we
must choose.
I suspect that all-numeric hostnames should have priority, for three
reasons: 1) they are probably more common than uses of no-dots IP
numbers and thus we minimize user surprises; 2) RFC 1123 says it MUST be
supported; and 3) no-dots IP numbers can always be converted to
dotted-quad IP numbers.
I propose that we (Debian) modify gethostbyname so that it does not
interpret an all-numeric string as an IP number, although consultation
with glibc upstream first might be good. Offhand, it would seem like
adding a special-case test to nss/getXXbyYY.c or by changing
nss/digits_dots.c would be the way to do this, though I haven't looked
at how big repercussions changes to either of those would have.
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