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c-ares/docs/ares_init_options.3

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Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
.\"
.\" Copyright 1998 by the Massachusetts Institute of Technology.
.\" Copyright (C) 2004-2010 by Daniel Stenberg
.\"
.\" Permission to use, copy, modify, and distribute this
.\" software and its documentation for any purpose and without
.\" fee is hereby granted, provided that the above copyright
.\" notice appear in all copies and that both that copyright
.\" notice and this permission notice appear in supporting
.\" documentation, and that the name of M.I.T. not be used in
.\" advertising or publicity pertaining to distribution of the
.\" software without specific, written prior permission.
.\" M.I.T. makes no representations about the suitability of
.\" this software for any purpose. It is provided "as is"
.\" without express or implied warranty.
.\"
provide SPDX identifiers and a REUSE CI job to verify All files have their licence and copyright information clearly identifiable. If not in the file header, they are set separately in .reuse/dep5. All used license texts are provided in LICENSES/
2 years ago
.\" SPDX-License-Identifier: MIT
.\"
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
.TH ARES_INIT 3 "5 March 2010"
.SH NAME
ares_init_options \- Initialize a resolver channel
.SH SYNOPSIS
.nf
#include <ares.h>
struct ares_options {
int flags;
int timeout; /* in seconds or milliseconds, depending on options */
int tries;
int ndots;
unsigned short udp_port;
unsigned short tcp_port;
int socket_send_buffer_size;
int socket_receive_buffer_size;
struct in_addr *servers;
int nservers;
char **domains;
int ndomains;
char *lookups;
ares_sock_state_cb sock_state_cb;
void *sock_state_cb_data;
struct apattern *sortlist;
int nsort;
int ednspsz;
char *resolvconf_path;
Configurable hosts path for file_lookup (#465) This changeset adds support for configurable hosts file ARES_OPT_HOSTS_FILE (similar to ARES_OPT_RESOLVCONF). Co-authored-by: Manish Mehra (@mmehra)
3 years ago
char *hosts_path;
Configuration option to limit number of UDP queries per ephemeral port (#549) Add a new ARES_OPT_UDP_MAX_QUERIES option with udp_max_queries parameter that can be passed to ares_init_options(). This value defaults to 0 (unlimited) to maintain existing compatibility, any positive number will cause new UDP ephemeral ports to be created once the threshold is reached, we'll call these 'connections' even though its technically wrong for UDP. Implementation Details: * Each server entry in a channel now has a linked-list of connections/ports for udp and tcp. The first connection in the list is the one most likely to be eligible to accept new queries. * Queries are now tracked by connection rather than by server. * Every time a query is detached from a connection, the connection that it was attached to will be checked to see if it needs to be cleaned up. * Insertion, lookup, and searching for connections has been implemented as O(1) complexity so the number of connections will not impact performance. * Remove is_broken from the server, it appears it would be set and immediately unset, so must have been invalidated via a prior patch. A future patch should probably track consecutive server errors and de-prioritize such servers. The code right now will always try servers in the order of configuration, so a bad server in the list will always be tried and may rely on timeout logic to try the next. * Various other cleanups to remove code duplication and for clarification. Fixes Bug: #444 Fix By: Brad House (@bradh352)
1 year ago
int udp_max_queries;
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
};
int ares_init_options(ares_channel *\fIchannelptr\fP,
struct ares_options *\fIoptions\fP,
int \fIoptmask\fP)
.fi
.SH DESCRIPTION
The \fBares_init_options(3)\fP function initializes a communications channel
for name service lookups. If it returns successfully,
\fBares_init_options(3)\fP will set the variable pointed to by
\fIchannelptr\fP to a handle used to identify the name service channel. The
caller should invoke \fIares_destroy(3)\fP on the handle when the channel is
no longer needed.
The \fIoptmask\fP parameter generally specifies which fields in the structure pointed to
by \fIoptions\fP are set, as follows:
.TP 18
.B ARES_OPT_FLAGS
.B int \fIflags\fP;
.br
Flags controlling the behavior of the resolver. See below for a
description of possible flag values.
.TP 18
.B ARES_OPT_TIMEOUT
.B int \fItimeout\fP;
.br
The number of seconds each name server is given to respond to a query on the
first try. (After the first try, the timeout algorithm becomes more
complicated, but scales linearly with the value of \fItimeout\fP.) The
its not 1991 anymore, lower default timeout and retry count (#542) A lot of time has passed since the original timeouts and retry counts were chosen. We have on and off issues reported due to this. Even on geostationary satellite links, latency is worst case around 1.5s. This PR changes the per-server timeout to 2s and the retry count lowered from 4 to 3. Fix By: Brad House (@bradh352)
1 year ago
default is two seconds. This option is being deprecated by
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
\fIARES_OPT_TIMEOUTMS\fP starting in c-ares 1.5.2.
.TP 18
.B ARES_OPT_TIMEOUTMS
.B int \fItimeout\fP;
.br
The number of milliseconds each name server is given to respond to a query on
the first try. (After the first try, the timeout algorithm becomes more
complicated, but scales linearly with the value of \fItimeout\fP.) The
its not 1991 anymore, lower default timeout and retry count (#542) A lot of time has passed since the original timeouts and retry counts were chosen. We have on and off issues reported due to this. Even on geostationary satellite links, latency is worst case around 1.5s. This PR changes the per-server timeout to 2s and the retry count lowered from 4 to 3. Fix By: Brad House (@bradh352)
1 year ago
default is two seconds. Note that this option is specified with the same
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
struct field as the former \fIARES_OPT_TIMEOUT\fP, it is but the option bits
that tell c-ares how to interpret the number. This option was added in c-ares
1.5.2.
.TP 18
.B ARES_OPT_TRIES
.B int \fItries\fP;
.br
The number of tries the resolver will try contacting each name server
its not 1991 anymore, lower default timeout and retry count (#542) A lot of time has passed since the original timeouts and retry counts were chosen. We have on and off issues reported due to this. Even on geostationary satellite links, latency is worst case around 1.5s. This PR changes the per-server timeout to 2s and the retry count lowered from 4 to 3. Fix By: Brad House (@bradh352)
1 year ago
before giving up. The default is three tries.
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
.TP 18
.B ARES_OPT_NDOTS
.B int \fIndots\fP;
.br
The number of dots which must be present in a domain name for it to be
queried for "as is" prior to querying for it with the default domain
extensions appended. The default value is 1 unless set otherwise by
resolv.conf or the RES_OPTIONS environment variable.
.TP 18
.B ARES_OPT_UDP_PORT
.B unsigned short \fIudp_port\fP;
.br
docs: ARES_OPT_UDP_PORT and ARES_OPT_TCP_PORT docs wrong byte order As per #487, documentation states the port should be in network byte order, but we can see from the test cases using MockServers on different ports that this is not the case, it is definitely in host byte order. Fix By: Brad House (@bradh352)
2 years ago
The port to use for queries over UDP, in host byte order.
The default value is 53, the standard name service port.
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
.TP 18
.B ARES_OPT_TCP_PORT
.B unsigned short \fItcp_port\fP;
.br
docs: ARES_OPT_UDP_PORT and ARES_OPT_TCP_PORT docs wrong byte order As per #487, documentation states the port should be in network byte order, but we can see from the test cases using MockServers on different ports that this is not the case, it is definitely in host byte order. Fix By: Brad House (@bradh352)
2 years ago
The port to use for queries over TCP, in host byte order.
The default value is 53, the standard name service port.
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
.TP 18
.B ARES_OPT_SERVERS
.B struct in_addr *\fIservers\fP;
.br
.B int \fInservers\fP;
.br
The list of IPv4 servers to contact, instead of the servers specified in
docs: provide better man page references When referring to another c-ares function use \fI function(3) \fP to let the webpage rendering find and cross-link them appropriately. SEE ALSO references should be ".BR name (3),", with a space before the open parenthesis. This helps the manpage to HTML renderer. Closes #565
1 year ago
resolv.conf or the local named. In order to allow specification of either IPv4
or IPv6 name servers, the \Bares_set_servers(3)\fP function must be used
instead.
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
.TP 18
.B ARES_OPT_DOMAINS
.B char **\fIdomains\fP;
.br
.B int \fIndomains\fP;
.br
The domains to search, instead of the domains specified in resolv.conf
or the domain derived from the kernel hostname variable.
.TP 18
.B ARES_OPT_LOOKUPS
.B char *\fIlookups\fP;
.br
The lookups to perform for host queries.
.I lookups
should be set to a string of the characters "b" or "f", where "b"
indicates a DNS lookup and "f" indicates a lookup in the hosts file.
.TP 18
.B ARES_OPT_SOCK_STATE_CB
.B void (*\fIsock_state_cb\fP)(void *data, ares_socket_t socket_fd, int readable, int writable);
.br
.B void *\fIsock_state_cb_data\fP;
.br
A callback function to be invoked when a socket changes state.
.I socket_fd
will be passed the socket whose state has changed;
.I readable
will be set to true if the socket should listen for read events, and
.I writable
will be set to true if the socket should listen for write events.
The value of
.I sock_state_cb_data
will be passed as the
.I data
argument.
.TP 18
.B ARES_OPT_SORTLIST
.B struct apattern *\fIsortlist\fP;
.br
.B int \fInsort\fP;
.br
A list of IP address ranges that specifies the order of preference that
results from \fIares_gethostbyname\fP should be returned in. Note that
this can only be used with a sortlist retrieved via
\fBares_save_options(3)\fP (because
.B struct apattern
is opaque); to set a fresh sort list, use \fBares_set_sortlist(3)\fP.
.TP 18
.B ARES_OPT_SOCK_SNDBUF
.B int \fIsocket_send_buffer_size\fP;
.br
The send buffer size to set for the socket.
.TP 18
.B ARES_OPT_SOCK_RCVBUF
.B int \fIsocket_receive_buffer_size\fP;
.br
The receive buffer size to set for the socket.
.TP 18
.B ARES_OPT_EDNSPSZ
.B int \fIednspsz\fP;
.br
The message size to be advertized in EDNS; only takes effect if the
.B ARES_FLAG_EDNS
flag is set.
.TP 18
.B ARES_OPT_RESOLVCONF
.B char *\fIresolvconf_path\fP;
.br
The path to use for reading the resolv.conf file. The
.I resolvconf_path
should be set to a path string, and will be honoured on *nix like systems. The
default is
.B /etc/resolv.conf
.br
Configurable hosts path for file_lookup (#465) This changeset adds support for configurable hosts file ARES_OPT_HOSTS_FILE (similar to ARES_OPT_RESOLVCONF). Co-authored-by: Manish Mehra (@mmehra)
3 years ago
.TP 18
.B ARES_OPT_HOSTS_FILE
.B char *\fIhosts_path\fP;
.br
The path to use for reading the hosts file. The
.I hosts_path
should be set to a path string, and will be honoured on *nix like systems. The
default is
.B /etc/hosts
.br
Configuration option to limit number of UDP queries per ephemeral port (#549) Add a new ARES_OPT_UDP_MAX_QUERIES option with udp_max_queries parameter that can be passed to ares_init_options(). This value defaults to 0 (unlimited) to maintain existing compatibility, any positive number will cause new UDP ephemeral ports to be created once the threshold is reached, we'll call these 'connections' even though its technically wrong for UDP. Implementation Details: * Each server entry in a channel now has a linked-list of connections/ports for udp and tcp. The first connection in the list is the one most likely to be eligible to accept new queries. * Queries are now tracked by connection rather than by server. * Every time a query is detached from a connection, the connection that it was attached to will be checked to see if it needs to be cleaned up. * Insertion, lookup, and searching for connections has been implemented as O(1) complexity so the number of connections will not impact performance. * Remove is_broken from the server, it appears it would be set and immediately unset, so must have been invalidated via a prior patch. A future patch should probably track consecutive server errors and de-prioritize such servers. The code right now will always try servers in the order of configuration, so a bad server in the list will always be tried and may rely on timeout logic to try the next. * Various other cleanups to remove code duplication and for clarification. Fixes Bug: #444 Fix By: Brad House (@bradh352)
1 year ago
.TP 18
.B ARES_OPT_UDP_MAX_QUERIES
.B int \fIudp_max_queries\fP;
.br
The maximum number of udp queries that can be sent on a single ephemeral port
to a given DNS server before a new ephemeral port is assigned. Any value of 0
or less will be considered unlimited, and is the default.
.br
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
.PP
The \fIoptmask\fP parameter also includes options without a corresponding
field in the
.B ares_options
structure, as follows:
.TP 23
.B ARES_OPT_ROTATE
Perform round-robin selection of the nameservers configured for the channel
for each resolution.
.TP 23
.B ARES_OPT_NOROTATE
Do not perform round-robin nameserver selection; always use the list of
nameservers in the same order.
.PP
The
.I flags
field should be the bitwise or of some subset of the following values:
.TP 23
.B ARES_FLAG_USEVC
Always use TCP queries (the "virtual circuit") instead of UDP
queries. Normally, TCP is only used if a UDP query yields a truncated
result.
.TP 23
.B ARES_FLAG_PRIMARY
Only query the first server in the list of servers to query.
.TP 23
.B ARES_FLAG_IGNTC
If a truncated response to a UDP query is received, do not fall back
to TCP; simply continue on with the truncated response.
.TP 23
.B ARES_FLAG_NORECURSE
Do not set the "recursion desired" bit on outgoing queries, so that the name
server being contacted will not try to fetch the answer from other servers if
it doesn't know the answer locally. Be aware that ares will not do the
recursion for you. Recursion must be handled by the application calling ares
if \fIARES_FLAG_NORECURSE\fP is set.
.TP 23
.B ARES_FLAG_STAYOPEN
Do not close communications sockets when the number of active queries
drops to zero.
.TP 23
.B ARES_FLAG_NOSEARCH
Do not use the default search domains; only query hostnames as-is or
as aliases.
.TP 23
.B ARES_FLAG_NOALIASES
Do not honor the HOSTALIASES environment variable, which normally
specifies a file of hostname translations.
.TP 23
.B ARES_FLAG_NOCHECKRESP
Do not discard responses with the SERVFAIL, NOTIMP, or REFUSED
response code or responses whose questions don't match the questions
in the request. Primarily useful for writing clients which might be
used to test or debug name servers.
.TP 23
.B ARES_FLAG_EDNS
Include an EDNS pseudo-resource record (RFC 2671) in generated requests.
.SH RETURN VALUES
\fBares_init_options(3)\fP can return any of the following values:
.TP 14
.B ARES_SUCCESS
Initialization succeeded.
.TP 14
.B ARES_EFILE
A configuration file could not be read.
.TP 14
.B ARES_ENOMEM
The process's available memory was exhausted.
.TP 14
.B ARES_ENOTINITIALIZED
c-ares library initialization not yet performed.
.SH NOTES
When initializing from
.B /etc/resolv.conf,
(or, alternatively when specified by the
.I resolvconf_path
path location)
\fBares_init_options(3)\fP reads the \fIdomain\fP and \fIsearch\fP directives
to allow lookups of short names relative to the domains specified. The
Fix a typo in ares_init_options.3 (#510) that -> than Fix By: Yijie Ma (@yijiem)
2 years ago
\fIdomain\fP and \fIsearch\fP directives override one another. If more than
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
one instance of either \fIdomain\fP or \fIsearch\fP directives is specified,
the last occurrence wins. For more information, please see the
.BR resolv.conf (5)
manual page.
.SH SEE ALSO
docs: provide better man page references When referring to another c-ares function use \fI function(3) \fP to let the webpage rendering find and cross-link them appropriately. SEE ALSO references should be ".BR name (3),", with a space before the open parenthesis. This helps the manpage to HTML renderer. Closes #565
1 year ago
.BR ares_init (3),
.BR ares_destroy (3),
.BR ares_dup (3),
.BR ares_library_init (3),
.BR ares_save_options (3),
.BR ares_set_servers (3),
.BR ares_set_sortlist (3)
Avoid buffer overflow in RC4 loop comparison (#336) The rc4 function iterates over a buffer of size buffer_len who's maximum value is INT_MAX with a counter of type short that is not guaranteed to have maximum size INT_MAX. In circumstances where short is narrower than int and where buffer_len is larger than the maximum value of a short, it may be possible to loop infinitely as counter will overflow and never be greater than or equal to buffer_len. The solution is to make the comparison be between types of equal width. This commit defines counter as an int. Fix By: Fionn Fitzmaurice (@fionn)
4 years ago
.SH AUTHOR
Greg Hudson, MIT Information Systems
.br
Copyright 1998 by the Massachusetts Institute of Technology.
.br
Copyright (C) 2004-2010 by Daniel Stenberg.