search is only performed if the search or domain keyword is used in
resolv.conf and the queried name has fewer than ndots dots. there is
no default domain and names with >=ndots dots are never subjected to
search; failure in the root scope is final.

the (non-POSIX) res_search API presently does not honor search. this
may be added at some point in the future if needed.

resolv.conf is now parsed twice, at two different layers of the code
involved. this will be fixed in a subsequent patch.

rcode of 3 (NxDomain) was treated as a hard EAI_NONAME failure, but it
should instead return 0 (no results) so the caller can continue
searching. this will be important for adding search domain support.
the top-level caller will automatically return EAI_NONAME if there are
zero results at the end.

also, the case where rcode is 0 (success) but there are no results was
not handled. this happens when the domain exists but there are no A or
AAAA records for it. in this case a hard EAI_NONAME should be imposed
to inhibit further search, since the name was defined and just does
not have any address associated with it. previously a misleading hard
failure of EAI_FAIL was reported.

this change is made in preparation for adding search domains, for
which higher-level code will need to parse resolv.conf. simply parsing
it twice for each lookup would be one reasonable option, but the
existing parser code was buggy anyway, which suggested to me that it's
a bad idea to have two variants of this code in two different places.

the old code in res_msend potentially misinterpreted overly long lines
in resolv.conf, and stopped parsing after it found 3 nameservers, even
if there were relevant options left to be parsed later in the file.

The return value of if_nametoindex is unsigned; it should return 0
on error.

With point-to-point interfaces, the IFA_ADDRESS netlink attribute
contains the peer address while an extra attribute IFA_LOCAL carries
the actual local interface address.

Both the glibc and uclibc implementations of getifaddrs() handle this
case by moving the ifa_addr contents to the broadcast/remote address
union and overwriting ifa_addr upon receipt of an IFA_LOCAL attribute.

This patch adds the same special treatment logic of IFA_LOCAL to
musl's implementation of getifaddrs() in order to align its behaviour
with that of uclibc and glibc.
Signed-off-by: NJo-Philipp Wich <jow@openwrt.org>

getnameinfo() compares the size of the given struct sockaddr with
sizeof(struct sockaddr_in) and sizeof(struct sockaddr_in6) depending on
the net family. When you add a sockaddr of size sizeof(struct
sockaddr_storage) this function will fail because the size of the
sockaddr is too big. Change the check that it only fails if the size is
too small, but make it work when it is too big for example when someone
calls this function with a struct sockaddr_storage and its size.
This fixes a problem with IoTivity 1.0.0 and musl.

glibc and bionic are only failing if it is smaller, net/freebsd
implemented the != check.
Signed-off-by: NHauke Mehrtens <hauke@hauke-m.de>

previously, transient failures like fd exhaustion or other
resource-related errors were treated the same as non-existence of
these files, leading to fallbacks or false-negative results. in
particular:

- failure to open hosts resulted in fallback to dns, possibly yielding
  EAI_NONAME for a hostname that should be defined locally, or an
  unwanted result from dns that the hosts file was intended to
  replace.

- failure to open services resulted in EAI_SERVICE.

- failure to open resolv.conf resulted in querying localhost rather
  than the configured nameservers.

now, only permanent errors trigger the fallback behaviors above; all
other errors are reportable to the caller as EAI_SYSTEM.

previously, __lookup_ipliteral only checked its argument against the
requested address family, so IPv4 literals passed through to
__lookup_name if the caller asked for only IPv6 results, and likewise
for IPv6 literals when the caller asked for only IPv4. this resulted
in spurious DNS lookups that reportedly even succeeded with some
nameservers.

now, __lookup_ipliteral attempts to parse its argument as both IPv4
and IPv6, and returns an error (to stop further search) rather than 0
(no results yet) if the form of the argument mismatches the requested
address family.

based on patch by Julien Ramseier.

this case is specified as a mandatory ("shall fail") error.

based on patch by Julien Ramseier.

due to a reversed pointer difference computation, ns_skiprr always
returned a negative value, which functions using it would interpret as
an error.

patch by Yu Lu.

one stop condition for parsing abbreviated ipv6 addressed was missed,
allowing the internal ip[] buffer to overflow. this patch adds the
missing stop condition and masks the array index so that, in case
there are any remaining stop conditions missing, overflowing the
buffer is not possible.

all socket types are accepted at this point, but that may be changed
at a later time if the behavior is not meaningful for other types. as
before, omitting type (a value of 0) gives both UDP and TCP results,
and SOCK_DGRAM or SOCK_STREAM restricts to UDP or TCP, respectively.
for other socket types, the service name argument is required to be a
null pointer, and the protocol number provided by the caller is used.

based on patch by Timo Teräs, with some corrections to bounds checking
code and other minor changes.

while they are borderline scope creep, the functions added are fairly
small and are roughly the minimum code needed to use the results of
the res_query API without re-implementing error-prone DNS packet
parsing, and they are used in practice by some kerberos related
software and possibly other things. at this time there is no intent to
implement further nameser.h API functions.

if the loop stopped due to reaching the end of the string, the
subsequent increment could possibly move the position one past the end
of the buffer. no further writes happen, the reads cannot fault anyway
unless the stack completely lacks any zero bytes, and reading junk
should not yield an incorrect result from the function either.
nonetheless the code was wrong and needs to be fixed.

the condition was probably intended to be !*p rather than !p, but
neither is needed here. the subsequent code naturally handles the case
where it's already at end of string.

the outer getnameinfo function already has a properly-sized temporary
buffer for storing the reverse dns (ptr) result. there is no reason
for the callback to use a secondary buffer and copy it on success, and
doing so potentially expanded the impact of the dn_expand bug that was
fixed in commit 49d2c8c6.

this change reduces the code size by a small amount, and also reduces
the run-time stack space requirements by about 256 bytes.

Empty name was rejected in dn_expand since commit
56b57f37
which is a regression as reported by Natanael Copa.

Furthermore if an offset pointer in a compressed name
pointed to a terminating 0 byte (instead of a label)
the returned name was not null terminated.

the previous implementations had several deficiencies, the most severe
of which was the inability to report unconfigured interfaces or
interfaces without ipv4 addresses. among the options discussed for
fixing this, using netlink turned out to be the one with the least
cost and most additional advantages. other improvements include:

if_nameindex now avoids duplicates in the list it produces, but still
includes legacy-style interface aliases if any are in use.

getifaddrs now reports hardware addresses and includes the scope_id
for link-local ipv6 addresses in the resulting address.

for LC_MESSAGES, translation of strerror and similar literal message
functions is supported. for messages in other places (particularly the
dynamic linker) that use format strings, translation is not yet
supported. in order to make it possible and safe, such messages will
need to be refactored to separate the textual content from the format.

for LC_TIME, the day and month names and strftime-style format strings
provided by nl_langinfo are supported for translation. however there
may be limitations, as some of the original C-locale nl_langinfo
strings are non-unique and thus perhaps non-suitable as keys.

overall, the locale support activated by this commit should not be
seen as complete and polished but as a basis for beginning to test
locale functionality and implement locales.

iptables and quagga need them to work.

according to the documentation in the man pages, the GNU extension
functions gethostbyaddr_r, gethostbyname_r and gethostbyname2_r are
guaranteed to set the result pointer to NULL in case of error or no
result.

this case is not even documented, but the kernel returns 0 here and it
makes sense to be consistent.

these are not pure syscall wrappers because they have to work around
kernel API bugs on 64-bit archs. the workarounds could probably be
made somewhat more efficient, but at the cost of more complexity. this
may be revisited later.

the results of a dns query, whether it's performed as part of one of
the standard name-resolving functions or directly by res_send, should
be a function of the query, not of the particular nameserver that
responds to it. thus, all responses which indicate a failure or
refusal by the nameserver, as opposed to a positive or negative result
for the query, should be ignored.

the strategy used is to re-issue the query immediately (but with a
limit on the number of retries, in case the server is really broken)
when a response code of 2 (server failure, typically transient) is
seen, and otherwise take no action on bad responses (which generally
indicate a misconfigured nameserver or one which the client does not
have permission to use), allowing the normal retry interval to apply
and of course accepting responses from other nameservers queried in
parallel.

empirically this matches the traditional resolver behavior for
nameservers that respond with a code of 2 in the case where there is
just a single nameserver configured. the behavior diverges when
multiple nameservers are available, since musl is querying them in
parallel. in this case we are mildly more aggressive at retrying.

the fcntl function is heavy, so make the syscall directly instead.
also, avoid the code size and runtime overhead of querying the old
flags, since it's reasonable to assume nothing will be set on a
newly-created socket. this code is only used on old kernels which lack
proper atomic close-on-exec support, so future changes that might
invalidate such an assumption do not need to be considered.

as usual, this is non-atomic, but better than producing an error or
failing to set the close-on-exec flag at all.

the input name is validated, the other parameters are assumed to be
valid (the list of already compressed names are not checked for
infinite reference loops or out-of-bound offsets).

names are handled case-sensitively for now.

trailing . should be accepted in domain name strings by convention
(RFC 1034), host name lookup accepts "." but rejects empty "", res_*
interfaces also accept empty name following existing practice.

A domain name is at most 255 bytes long (RFC 1035), but the string
representation is two bytes smaller so the strlen maximum is 253.

Due to an error introduced in commit fcc522c9,
checking of the remaining output buffer space was not performed correctly,
allowing malformed input to write past the end of the buffer.

In addition, the loop detection logic failed to account for the possibility
of infinite loops with no output, which would hang the function.

The output size is now limited more strictly so only names with valid length
are accepted.

this also affects the legacy getservbyport family, which uses
getnameinfo as its backend.

this also affects the legacy gethostbyaddr family, which uses
getnameinfo as its backend.

some other minor changes associated with the refactoring of source
files are also made; in particular, the resolv.conf parser now uses
the same code that's used elsewhere to handle ip literals, so as a
side effect it can now accept a scope id for nameserver addressed with
link-local scope.