Re: [PATCH] dns: Apply a default TTL to records obtained from getaddrinfo()
From: David Howells
Date: Tue May 19 2020 - 09:39:58 EST
Ben Boeckel <me@xxxxxxxxxxxxxx> wrote:
> Is there precedent for this config file format?
Okay, I can change it to:
default_ttl = <number-of-seconds>
and strip spaces all over the place.
> But no trailing whitespace is allowed?
Yes... See a few lines above:
while (p > buf && isspace(p[-1]))
p--;
*p = 0;
> The valid range should be mentioned in the docs (basically that 0 is not
> allowed and has no special meaning (it could mean leaving off the TTL as
> previously done)).
I suppose - that's mainly to make sure I'm not passing an invalid value to the
syscall.
> Forwards compatibility is hard with such behavior. Is there any reason
> this can't be a warning?
I can downgrade it to a warning. I'm not sure that there's any problem here,
but I have met circumstances before where it is the wrong thing to ignore an
explicit option that you don't support rather than giving an error.
> There's no mention of the leading whitespace support or comments here.
> Does the file deserve its own manpage?
Um. I'm not sure. Quite possibly there should at least be a stub file with a
.so directive in it.
Anyway, how about the attached?
David
---
commit cbf0457e0fc99aa5beabe54daeda57be70dfdfce
Author: David Howells <dhowells@xxxxxxxxxx>
Date: Tue Apr 14 16:07:26 2020 +0100
dns: Apply a default TTL to records obtained from getaddrinfo()
Address records obtained from getaddrinfo() don't come with any TTL
information, even if they're obtained from the DNS, with the result that
key.dns_resolver upcall program doesn't set an expiry time on dns_resolver
records unless they include a component obtained directly from the DNS,
such as an SRV or AFSDB record.
Fix this to apply a default TTL of 10mins in the event that we haven't got
one. This can be configured in /etc/keyutils/key.dns_resolver.conf by
adding the line:
default_ttl = <number-of-seconds>
to the file.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
diff --git a/Makefile b/Makefile
index 6f79446b..4d055701 100644
--- a/Makefile
+++ b/Makefile
@@ -202,6 +202,7 @@ endif
$(INSTALL) -D key.dns_resolver $(DESTDIR)$(SBINDIR)/key.dns_resolver
$(INSTALL) -D -m 0644 request-key.conf $(DESTDIR)$(ETCDIR)/request-key.conf
mkdir -p $(DESTDIR)$(ETCDIR)/request-key.d
+ mkdir -p $(DESTDIR)$(ETCDIR)/keyutils
mkdir -p $(DESTDIR)$(MAN1)
$(INSTALL) -m 0644 $(wildcard man/*.1) $(DESTDIR)$(MAN1)
mkdir -p $(DESTDIR)$(MAN3)
diff --git a/dns.afsdb.c b/dns.afsdb.c
index fa60e04f..986c0f38 100644
--- a/dns.afsdb.c
+++ b/dns.afsdb.c
@@ -37,8 +37,6 @@
*/
#include "key.dns.h"
-static unsigned long afs_ttl = ULONG_MAX;
-
/*
*
*/
@@ -114,8 +112,8 @@ static void afsdb_hosts_to_addrs(ns_msg handle, ns_sect section)
}
}
- afs_ttl = ttl;
- info("ttl: %u", ttl);
+ key_expiry = ttl;
+ info("ttl: %u", key_expiry);
}
/*
@@ -203,8 +201,8 @@ static void srv_hosts_to_addrs(ns_msg handle, ns_sect section)
}
}
- afs_ttl = ttl;
- info("ttl: %u", ttl);
+ key_expiry = ttl;
+ info("ttl: %u", key_expiry);
}
/*
@@ -240,7 +238,7 @@ static int dns_query_AFSDB(const char *cell)
/* look up the hostnames we've obtained to get the actual addresses */
afsdb_hosts_to_addrs(handle, ns_s_an);
- info("DNS query AFSDB RR results:%u ttl:%lu", payload_index, afs_ttl);
+ info("DNS query AFSDB RR results:%u ttl:%u", payload_index, key_expiry);
return 0;
}
@@ -279,7 +277,7 @@ static int dns_query_VL_SRV(const char *cell)
/* look up the hostnames we've obtained to get the actual addresses */
srv_hosts_to_addrs(handle, ns_s_an);
- info("DNS query VL SRV RR results:%u ttl:%lu", payload_index, afs_ttl);
+ info("DNS query VL SRV RR results:%u ttl:%u", payload_index, key_expiry);
return 0;
}
@@ -293,7 +291,7 @@ void afs_instantiate(const char *cell)
/* set the key's expiry time from the minimum TTL encountered */
if (!debug_mode) {
- ret = keyctl_set_timeout(key, afs_ttl);
+ ret = keyctl_set_timeout(key, key_expiry);
if (ret == -1)
error("%s: keyctl_set_timeout: %m", __func__);
}
diff --git a/key.dns.h b/key.dns.h
index b143f4a4..33d0ab3b 100644
--- a/key.dns.h
+++ b/key.dns.h
@@ -29,6 +29,7 @@
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
+#include <ctype.h>
#define MAX_VLS 15 /* Max Volume Location Servers Per-Cell */
#define INET_IP4_ONLY 0x1
@@ -42,6 +43,7 @@
extern key_serial_t key;
extern int debug_mode;
extern unsigned mask;
+extern unsigned int key_expiry;
#define N_PAYLOAD 256
extern struct iovec payload[N_PAYLOAD];
@@ -52,6 +54,8 @@ void error(const char *fmt, ...);
extern __attribute__((format(printf, 1, 2)))
void _error(const char *fmt, ...);
extern __attribute__((format(printf, 1, 2)))
+void warning(const char *fmt, ...);
+extern __attribute__((format(printf, 1, 2)))
void info(const char *fmt, ...);
extern __attribute__((noreturn))
void nsError(int err, const char *domain);
diff --git a/key.dns_resolver.c b/key.dns_resolver.c
index 4ac27d30..c241eda3 100644
--- a/key.dns_resolver.c
+++ b/key.dns_resolver.c
@@ -46,10 +46,13 @@ static const char key_type[] = "dns_resolver";
static const char a_query_type[] = "a";
static const char aaaa_query_type[] = "aaaa";
static const char afsdb_query_type[] = "afsdb";
+static const char *config_file = "/etc/keyutils/key.dns_resolver.conf";
+static bool config_specified = false;
key_serial_t key;
static int verbose;
int debug_mode;
unsigned mask = INET_ALL;
+unsigned int key_expiry = 10 * 60;
/*
@@ -105,6 +108,23 @@ void _error(const char *fmt, ...)
va_end(va);
}
+/*
+ * Pring a warning to stderr or the syslog
+ */
+void warning(const char *fmt, ...)
+{
+ va_list va;
+
+ va_start(va, fmt);
+ if (isatty(2)) {
+ vfprintf(stderr, fmt, va);
+ fputc('\n', stderr);
+ } else {
+ vsyslog(LOG_WARNING, fmt, va);
+ }
+ va_end(va);
+}
+
/*
* Print status information
*/
@@ -272,6 +292,7 @@ void dump_payload(void)
}
info("The key instantiation data is '%s'", buf);
+ info("The expiry time is %us", key_expiry);
free(buf);
}
@@ -412,6 +433,9 @@ int dns_query_a_or_aaaa(const char *hostname, char *options)
/* load the key with data key */
if (!debug_mode) {
+ ret = keyctl_set_timeout(key, key_expiry);
+ if (ret == -1)
+ error("%s: keyctl_set_timeout: %m", __func__);
ret = keyctl_instantiate_iov(key, payload, payload_index, 0);
if (ret == -1)
error("%s: keyctl_instantiate: %m", __func__);
@@ -420,6 +444,145 @@ int dns_query_a_or_aaaa(const char *hostname, char *options)
exit(0);
}
+/*
+ * Read the config file.
+ */
+static void read_config(void)
+{
+ FILE *f;
+ char buf[4096], *b, *p, *k, *v;
+ unsigned int line = 0, u;
+ int n;
+
+ printf("READ CONFIG %s\n", config_file);
+
+ f = fopen(config_file, "r");
+ if (!f) {
+ if (errno == ENOENT && !config_specified) {
+ debug("%s: %m", config_file);
+ return;
+ }
+ error("%s: %m", config_file);
+ }
+
+ while (fgets(buf, sizeof(buf) - 1, f)) {
+ line++;
+
+ /* Trim off leading and trailing spaces and discard whole-line
+ * comments.
+ */
+ b = buf;
+ while (isspace(*b))
+ b++;
+ if (!*b || *b == '#')
+ continue;
+ p = strchr(b, '\n');
+ if (!p)
+ error("%s:%u: line missing newline or too long", config_file, line);
+ while (p > buf && isspace(p[-1]))
+ p--;
+ *p = 0;
+
+ /* Split into key[=value] pairs and trim spaces. */
+ k = b;
+ v = NULL;
+ b = strchr(b, '=');
+ if (b) {
+ char quote = 0;
+ bool esc = false;
+
+ if (b == k)
+ error("%s:%u: Unspecified key",
+ config_file, line);
+
+ /* NUL-terminate the key. */
+ for (p = b - 1; isspace(*p); p--)
+ ;
+ p[1] = 0;
+
+ /* Strip leading spaces */
+ b++;
+ while (isspace(*b))
+ b++;
+ if (!*b)
+ goto missing_value;
+
+ if (*b == '"' || *b == '\'') {
+ quote = *b;
+ b++;
+ }
+ v = p = b;
+ while (*b) {
+ if (esc) {
+ esc = false;
+ *p++ = *b++;
+ continue;
+ }
+ if (*b == '\\') {
+ esc = true;
+ b++;
+ continue;
+ }
+ if (*b == quote) {
+ b++;
+ if (*b)
+ goto post_quote_data;
+ quote = 0;
+ break;
+ }
+ if (!quote && *b == '#')
+ break; /* Terminal comment */
+ *p++ = *b++;
+ }
+
+ if (esc)
+ error("%s:%u: Incomplete escape", config_file, line);
+ if (quote)
+ error("%s:%u: Unclosed quotes", config_file, line);
+ *p = 0;
+ }
+
+ if (strcmp(k, "default_ttl") == 0) {
+ if (!v)
+ goto missing_value;
+ if (sscanf(v, "%u%n", &u, &n) != 1)
+ goto bad_value;
+ if (v[n])
+ goto extra_data;
+ if (u < 1 || u > INT_MAX)
+ goto out_of_range;
+ key_expiry = u;
+ } else {
+ warning("%s:%u: Unknown option '%s'", config_file, line, k);
+ }
+ }
+
+ if (ferror(f) || fclose(f) == EOF)
+ error("%s: %m", config_file);
+ return;
+
+missing_value:
+ error("%s:%u: %s: Missing value", config_file, line, k);
+post_quote_data:
+ error("%s:%u: %s: Data after closing quote", config_file, line, k);
+bad_value:
+ error("%s:%u: %s: Bad value", config_file, line, k);
+extra_data:
+ error("%s:%u: %s: Extra data supplied", config_file, line, k);
+out_of_range:
+ error("%s:%u: %s: Value out of range", config_file, line, k);
+}
+
+/*
+ * Dump the configuration after parsing the config file.
+ */
+static __attribute__((noreturn))
+void config_dumper(void)
+{
+ printf("default_ttl = %u\n", key_expiry);
+ exit(0);
+}
+
/*
* Print usage details,
*/
@@ -428,22 +591,24 @@ void usage(void)
{
if (isatty(2)) {
fprintf(stderr,
- "Usage: %s [-vv] key_serial\n",
+ "Usage: %s [-vv] [-c config] key_serial\n",
prog);
fprintf(stderr,
- "Usage: %s -D [-vv] <desc> <calloutinfo>\n",
+ "Usage: %s -D [-vv] [-c config] <desc> <calloutinfo>\n",
prog);
} else {
- info("Usage: %s [-vv] key_serial", prog);
+ info("Usage: %s [-vv] [-c config] key_serial", prog);
}
exit(2);
}
-const struct option long_options[] = {
- { "debug", 0, NULL, 'D' },
- { "verbose", 0, NULL, 'v' },
- { "version", 0, NULL, 'V' },
- { NULL, 0, NULL, 0 }
+static const struct option long_options[] = {
+ { "config", 0, NULL, 'c' },
+ { "debug", 0, NULL, 'D' },
+ { "dump-config", 0, NULL, 2 },
+ { "verbose", 0, NULL, 'v' },
+ { "version", 0, NULL, 'V' },
+ { NULL, 0, NULL, 0 }
};
/*
@@ -455,11 +620,19 @@ int main(int argc, char *argv[])
char *keyend, *p;
char *callout_info = NULL;
char *buf = NULL, *name;
+ bool dump_config = false;
openlog(prog, 0, LOG_DAEMON);
- while ((ret = getopt_long(argc, argv, "vDV", long_options, NULL)) != -1) {
+ while ((ret = getopt_long(argc, argv, "c:vDV", long_options, NULL)) != -1) {
switch (ret) {
+ case 'c':
+ config_file = optarg;
+ config_specified = true;
+ continue;
+ case 2:
+ dump_config = true;
+ continue;
case 'D':
debug_mode = 1;
continue;
@@ -481,6 +654,9 @@ int main(int argc, char *argv[])
argc -= optind;
argv += optind;
+ read_config();
+ if (dump_config)
+ config_dumper();
if (!debug_mode) {
if (argc != 1)
@@ -542,7 +718,7 @@ int main(int argc, char *argv[])
name++;
info("Query type: '%*.*s'", qtlen, qtlen, keyend);
-
+
if ((qtlen == sizeof(a_query_type) - 1 &&
memcmp(keyend, a_query_type, sizeof(a_query_type) - 1) == 0) ||
(qtlen == sizeof(aaaa_query_type) - 1 &&
diff --git a/man/key.dns_resolver.8 b/man/key.dns_resolver.8
index e1882e06..0b17edd6 100644
--- a/man/key.dns_resolver.8
+++ b/man/key.dns_resolver.8
@@ -7,28 +7,41 @@
.\" as published by the Free Software Foundation; either version
.\" 2 of the License, or (at your option) any later version.
.\"
-.TH KEY.DNS_RESOLVER 8 "04 Mar 2011" Linux "Linux Key Management Utilities"
+.TH KEY.DNS_RESOLVER 8 "18 May 2020" Linux "Linux Key Management Utilities"
.SH NAME
key.dns_resolver \- upcall for request\-key to handle dns_resolver keys
.SH SYNOPSIS
\fB/sbin/key.dns_resolver \fR<key>
.br
-\fB/sbin/key.dns_resolver \fR\-D [\-v] [\-v] <keydesc> <calloutinfo>
+\fB/sbin/key.dns_resolver \fR--dump-config [\-c <configfile>]
+.br
+\fB/sbin/key.dns_resolver \fR\-D [\-v] [\-v] [\-c <configfile>] <desc>
+.br
+<calloutinfo>
.SH DESCRIPTION
This program is invoked by request\-key on behalf of the kernel when kernel
services (such as NFS, CIFS and AFS) want to perform a hostname lookup and the
kernel does not have the key cached. It is not ordinarily intended to be
called directly.
.P
-It can be called in debugging mode to test its functionality by passing a
-\fB\-D\fR flag on the command line. For this to work, the key description and
-the callout information must be supplied. Verbosity can be increased by
-supplying one or more \fB\-v\fR flags.
+There program has internal parameters that can be changed with a configuration
+file (see key.dns_resolver.conf(5) for more information). The default
+configuration file is in /etc, but this can be overridden with the \fB-c\fR
+flag.
+.P
+The program can be called in debugging mode to test its functionality by
+passing a \fB\-D\fR or \fB\--debug\fR flag on the command line. For this to
+work, the key description and the callout information must be supplied.
+Verbosity can be increased by supplying one or more \fB\-v\fR flags.
+.P
+The program may also be called with \fB--dump-config\fR to show the values that
+configurable parameters will have after parsing the config file.
.SH ERRORS
All errors will be logged to the syslog.
.SH SEE ALSO
.ad l
.nh
+.BR key.dns_resolver.conf (5),
.BR request\-key.conf (5),
.BR keyrings (7),
.BR request\-key (8)
diff --git a/man/key.dns_resolver.conf.5 b/man/key.dns_resolver.conf.5
new file mode 100644
index 00000000..03d04049
--- /dev/null
+++ b/man/key.dns_resolver.conf.5
@@ -0,0 +1,48 @@
+.\" -*- nroff -*-
+.\" Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+.\" Written by David Howells (dhowells@xxxxxxxxxx)
+.\"
+.\" This program is free software; you can redistribute it and/or
+.\" modify it under the terms of the GNU General Public License
+.\" as published by the Free Software Foundation; either version
+.\" 2 of the License, or (at your option) any later version.
+.\"
+.TH KEY.DNS_RESOLVER.CONF 5 "18 May 2020" Linux "Linux Key Management Utilities"
+.SH NAME
+key.dns_resolver.conf \- Kernel DNS resolver config
+.SH DESCRIPTION
+This file is used by the key.dns_resolver(5) program to set parameters.
+Unless otherwise overridden with the \fB\-c\fR flag, the program reads:
+.IP
+/etc/key.dns_resolver.conf
+.P
+Configuration options are given in \fBkey[=value]\fR form, where \fBvalue\fR is
+optional. If present, the value may be surrounded by a pair of single ('') or
+double quotes ("") which will be stripped off. The special characters in the
+value may be escaped with a backslash to turn them into ordinary characters.
+.P
+Lines beginning with a '#' are considered comments and ignored. A '#' symbol
+anywhere after the '=' makes the rest of the line into a comment unless the '#'
+is inside a quoted section or is escaped.
+.P
+Leading and trailing spaces and spaces around the '=' symbol will be stripped
+off.
+.P
+Available options include:
+.TP
+.B default_ttl=<number>
+The number of seconds to set as the expiration on a cached record. This will
+be overridden if the program manages to retrieve TTL information along with
+the addresses (if, for example, it accesses the DNS directly). The default is
+600 seconds. The value must be in the range 1 to INT_MAX.
+.P
+The file can also include comments beginning with a '#' character unless
+otherwise suppressed by being inside a quoted value or being escaped with a
+backslash.
+
+.SH FILES
+.ul
+/etc/key.dns_resolver.conf
+.ul 0
+.SH SEE ALSO
+\fBkey.dns_resolver\fR(8)