5089. [bug] Restore localhost fallback in dig and host which is
used when no nameserver addresses present in
/etc/resolv.conf are usable due to the requested
address family restrictions. [GL #433]
In BIND 9.11 and earlier, dig and similar tools used liblwres for
parsing /etc/resolv.conf. After getting a list of servers from
liblwres, a tool would check the address family of each server found and
reject those unusable. When the resulting list of usable servers was
empty, localhost addresses were queried as a fallback.
When liblwres was removed in BIND 9.12, dig and similar tools were
updated to parse /etc/resolv.conf using libirs instead. As part of that
process, the localhost fallback was removed from bin/dig/dighost.c since
the localhost fallback built into libirs was deemed to be sufficient.
However, libirs only falls back to localhost if it does not find any
name servers at all; if it does find any valid nameserver entry in
/etc/resolv.conf, it just returns it to the caller because it is
oblivious to whether the caller supports IPv4 and/or IPv6 or not. The
code in bin/dig/dighost.c subsequently filters the returned list of
servers in get_server_list() according to the requested address family
restrictions. This may result in none of the addresses returned by
libirs being usable, in which case a tool will attempt to work with an
empty server list, causing a hang and subsequently a crash upon user
interruption.
Restore the localhost fallback in bin/dig/dighost.c to prevent the
aforementioned hangs and crashes and ensure recent BIND versions behave
identically to the older ones in the circumstances described above.
If a tool using the routines defined in bin/dig/dighost.c is sent an
interruption signal around the time a connection timeout is scheduled to
fire, connect_timeout() may be executed after destroy_libs() detaches
from the global task (setting 'global_task' to NULL), which results in a
crash upon a UDP retry due to bringup_timer() attempting to create a
timer with 'task' set to NULL. Fix by preventing connect_timeout() from
attempting a retry when shutdown is in progress.
Resolve "Follow-up from "Redefine ISC's int and boolean types to use <stdint.h> and <stdbool.h> types""
Closes#449
See merge request isc-projects/bind9!998
