[PATCH] dns: Apply a default TTL to records obtained from getaddrinfo()
From: David Howells
Date: Mon May 18 2020 - 10:22:59 EST
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>
---
Makefile | 1 +
dns.afsdb.c | 16 ++++------
key.dns.h | 2 +
key.dns_resolver.c | 76 +++++++++++++++++++++++++++++++++++++++++++++---
man/key.dns_resolver.8 | 19 +++++++++++-
5 files changed, 100 insertions(+), 14 deletions(-)
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..e884cc4a 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];
diff --git a/key.dns_resolver.c b/key.dns_resolver.c
index 4ac27d30..df35493d 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;
/*
@@ -272,6 +275,7 @@ void dump_payload(void)
}
info("The key instantiation data is '%s'", buf);
+ info("The expiry time is %us", key_expiry);
free(buf);
}
@@ -412,6 +416,9 @@ 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 +427,61 @@ 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], *p;
+ 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++;
+ if (buf[0] == '#')
+ continue;
+ p = strchr(buf, '\n');
+ if (!p)
+ error("%s:%u: line missing newline or too long", config_file, line);
+ while (p > buf && isspace(p[-1]))
+ p--;
+ *p = 0;
+
+ if (strncmp(buf, "default_ttl:", 12) == 0) {
+ p = buf + 12;
+ while (isspace(*p))
+ p++;
+ if (sscanf(p, "%u%n", &u, &n) != 1)
+ error("%s:%u: default_ttl: Bad value",
+ config_file, line);
+ if (p[n])
+ error("%s:%u: default_ttl: Extra data supplied",
+ config_file, line);
+ if (u < 1 || u > INT_MAX)
+ error("%s:%u: default_ttl: Out of range",
+ config_file, line);
+ key_expiry = u;
+ } else {
+ error("%s:%u: Unknown option", config_file, line);
+ }
+ }
+
+ if (ferror(f) || fclose(f) == EOF)
+ error("%s: %m", config_file);
+}
+
/*
* Print usage details,
*/
@@ -428,18 +490,19 @@ 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[] = {
+ { "config", 0, NULL, 'c' },
{ "debug", 0, NULL, 'D' },
{ "verbose", 0, NULL, 'v' },
{ "version", 0, NULL, 'V' },
@@ -460,6 +523,10 @@ int main(int argc, char *argv[])
while ((ret = getopt_long(argc, argv, "vDV", long_options, NULL)) != -1) {
switch (ret) {
+ case 'c':
+ config_file = optarg;
+ config_specified = true;
+ continue;
case 'D':
debug_mode = 1;
continue;
@@ -481,6 +548,7 @@ int main(int argc, char *argv[])
argc -= optind;
argv += optind;
+ read_config();
if (!debug_mode) {
if (argc != 1)
@@ -542,7 +610,7 @@ 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..f7c44300 100644
--- a/man/key.dns_resolver.8
+++ b/man/key.dns_resolver.8
@@ -13,7 +13,9 @@ 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\-D [\-v] [\-v] [\-c <configfile>] <keydesc>
+.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
@@ -24,6 +26,21 @@ 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.
+.P
+A configuration file can be supplied to adjust various parameters. The file
+is looked for at:
+.IP
+/etc/keyutils/key.dns_resolver.conf
+.P
+unless otherwise specified with the \fB\-c\fR flag.
+.P
+Configuration 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.
.SH ERRORS
All errors will be logged to the syslog.
.SH SEE ALSO