[PATCH 0/8] ipconfig: NTP server support, bug fixes, documentation improvements

[PATCH 0/8] ipconfig: NTP server support, bug fixes, documentation improvements

[Chris Novakovic]

This series (against net-next) makes various improvements to ipconfig:

 - Patch #1 correctly documents the behaviour of parameter 4 in the
   "ip=" and "nfsaddrs=" command line parameter.
 - Patch #2 tidies up the printk()s for reporting configured name
   servers.
 - Patch #3 fixes a bug in autoconfiguration via BOOTP whereby the IP
   addresses of IEN-116 name servers are requested from the BOOTP
   server, rather than those of DNS name servers.
 - Patch #4 requests the number of DNS servers specified by
   CONF_NAMESERVERS_MAX when autoconfiguring via BOOTP, rather than
   hardcoding it to 2.
 - Patch #5 fully documents the contents and format of /proc/net/pnp in
   Documentation/filesystems/nfs/nfsroot.txt.
 - Patch #6 fixes a bug whereby bogus information is written to
   /proc/net/pnp when ipconfig is not used.
 - Patch #7 allows for NTP servers to be configured (manually on the
   kernel command line or automatically via DHCP), enabling systems with
   an NFS root filesystem to synchronise their clock before mounting
   their root filesystem.

Patch #7 gets a few warnings when run through checkpatch.pl, but I felt
it'd be better to use the same style as surrounding code where
appropriate, rather than adhering strictly to the net/ style guide.

Chris Novakovic (8):
  ipconfig: Document setting of NIS domain name
  ipconfig: Tidy up reporting of name servers
  ipconfig: BOOTP: Don't request IEN-116 name servers
  ipconfig: BOOTP: Request CONF_NAMESERVERS_MAX name servers
  ipconfig: Document /proc/net/pnp
  ipconfig: Correctly initialise ic_nameservers
  ipconfig: Write NTP server IPs to /proc/net/ntp
  CREDITS: Add Chris Novakovic

 CREDITS                                   |   4 +
 Documentation/filesystems/nfs/nfsroot.txt |  70 ++++++++++++++---
 net/ipv4/ipconfig.c                       | 121 +++++++++++++++++++++++++++---
 3 files changed, 174 insertions(+), 21 deletions(-)

-- 
2.14.1

[PATCH 1/8] ipconfig: Document setting of NIS domain name

[Chris Novakovic]

ic_do_bootp_ext() is responsible for parsing the "ip=" and "nfsaddrs="
kernel parameters. If a "." character is found in parameter 4 (the
client's hostname), everything before the first "." is used as the
hostname, and everything after it is used as the NIS domain name (but
not necessarily the DNS domain name).

Document this behaviour in Documentation/filesystems/nfs/nfsroot.txt,
as it is not made explicit.

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 Documentation/filesystems/nfs/nfsroot.txt | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/Documentation/filesystems/nfs/nfsroot.txt b/Documentation/filesystems/nfs/nfsroot.txt
index 5efae00f6c7f..1513e5d663fd 100644
--- a/Documentation/filesystems/nfs/nfsroot.txt
+++ b/Documentation/filesystems/nfs/nfsroot.txt
@@ -123,10 +123,13 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
 
 		Default:  Determined using autoconfiguration.
 
-  <hostname>	Name of the client. May be supplied by autoconfiguration,
-  		but its absence will not trigger autoconfiguration.
-		If specified and DHCP is used, the user provided hostname will
-		be carried in the DHCP request to hopefully update DNS record.
+  <hostname>	Name of the client. If a '.' character is present, anything
+		before the first '.' is used as the client's hostname, and anything
+		after it is used as its NIS domain name. May be supplied by
+		autoconfiguration, but its absence will not trigger autoconfiguration.
+		If specified and DHCP is used, the user-provided hostname (and NIS
+		domain name, if present) will be carried in the DHCP request; this
+		may cause a DNS record to be created or updated for the client.
 
   		Default: Client IP address is used in ASCII notation.
 
-- 
2.14.1

[PATCH 2/8] ipconfig: Tidy up reporting of name servers

[Chris Novakovic]

Commit 5e953778a2aab04929a5e7b69f53dc26e39b079e ("ipconfig: add
nameserver IPs to kernel-parameter ip=") adds the IP addresses of
discovered name servers to the summary printed by ipconfig when
configuration is complete. It appears the intention in ip_auto_config()
was to print the name servers on a new line (especially given the
spacing and lack of comma before "nameserver0="), but they're actually
printed on the same line as the NFS root filesystem configuration
summary:

  [    0.686186] IP-Config: Complete:
  [    0.686226]      device=eth0, hwaddr=xx:xx:xx:xx:xx:xx, ipaddr=10.0.0.2, mask=255.255.255.0, gw=10.0.0.1
  [    0.686328]      host=test, domain=example.com, nis-domain=(none)
  [    0.686386]      bootserver=10.0.0.1, rootserver=10.0.0.1, rootpath=     nameserver0=10.0.0.1

This makes it harder to read and parse ipconfig's output. Instead, print
the name servers on a separate line:

  [    0.791250] IP-Config: Complete:
  [    0.791289]      device=eth0, hwaddr=xx:xx:xx:xx:xx:xx, ipaddr=10.0.0.2, mask=255.255.255.0, gw=10.0.0.1
  [    0.791407]      host=test, domain=example.com, nis-domain=(none)
  [    0.791475]      bootserver=10.0.0.1, rootserver=10.0.0.1, rootpath=
  [    0.791476]      nameserver0=10.0.0.1

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 net/ipv4/ipconfig.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index 43f620feb1c4..d0ea0ecc9008 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -1481,16 +1481,19 @@ static int __init ip_auto_config(void)
 		&ic_servaddr, &root_server_addr, root_server_path);
 	if (ic_dev_mtu)
 		pr_cont(", mtu=%d", ic_dev_mtu);
-	for (i = 0; i < CONF_NAMESERVERS_MAX; i++)
+	/* Name servers (if any): */
+	for (i = 0; i < CONF_NAMESERVERS_MAX; i++) {
 		if (ic_nameservers[i] != NONE) {
-			pr_cont("     nameserver%u=%pI4",
-				i, &ic_nameservers[i]);
-			break;
+			if (i == 0)
+				pr_info("     nameserver%u=%pI4",
+					i, &ic_nameservers[i]);
+			else
+				pr_cont(", nameserver%u=%pI4",
+					i, &ic_nameservers[i]);
 		}
-	for (i++; i < CONF_NAMESERVERS_MAX; i++)
-		if (ic_nameservers[i] != NONE)
-			pr_cont(", nameserver%u=%pI4", i, &ic_nameservers[i]);
-	pr_cont("\n");
+		if (i + 1 == CONF_NAMESERVERS_MAX)
+			pr_cont("\n");
+	}
 #endif /* !SILENT */
 
 	/*
-- 
2.14.1

[PATCH 3/8] ipconfig: BOOTP: Don't request IEN-116 name servers

[Chris Novakovic]

When ipconfig is autoconfigured via BOOTP, the request packet
initialised by ic_bootp_init_ext() allocates 8 bytes for tag 5 ("Name
Server" [1, §3.7]), but tag 5 in the response isn't processed by
ic_do_bootp_ext(). Instead, allocate the 8 bytes to tag 6 ("Domain Name
Server" [1, §3.8]), which is processed by ic_do_bootp_ext(), and appears
to have been the intended tag to request.

This won't cause any breakage for existing users, as tag 5 responses
provided by BOOTP servers weren't being processed anyway.

[1] RFC 2132, "DHCP Options and BOOTP Vendor Extensions":
    https://tools.ietf.org/rfc/rfc2132.txt

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 net/ipv4/ipconfig.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index d0ea0ecc9008..bcf3c4f9882d 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -721,7 +721,7 @@ static void __init ic_bootp_init_ext(u8 *e)
 	*e++ = 3;		/* Default gateway request */
 	*e++ = 4;
 	e += 4;
-	*e++ = 5;		/* Name server request */
+	*e++ = 6;		/* (DNS) name server request */
 	*e++ = 8;
 	e += 8;
 	*e++ = 12;		/* Host name request */
-- 
2.14.1

[PATCH 4/8] ipconfig: BOOTP: Request CONF_NAMESERVERS_MAX name servers

[Chris Novakovic]

When ipconfig is autoconfigured via BOOTP, the request packet
initialised by ic_bootp_init_ext() always allocates 8 bytes for the name
server option, limiting the BOOTP server to responding with at most 2
name servers even though ipconfig in fact supports an arbitrary number
of name servers (as defined by CONF_NAMESERVERS_MAX, which is currently
3).

Only request name servers in the request packet if CONF_NAMESERVERS_MAX
is positive (to comply with [1, §3.8]), and allocate enough space in the
packet for CONF_NAMESERVERS_MAX name servers to indicate the maximum
number we can accept in response.

[1] RFC 2132, "DHCP Options and BOOTP Vendor Extensions":
    https://tools.ietf.org/rfc/rfc2132.txt

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 net/ipv4/ipconfig.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index bcf3c4f9882d..0f460d6d3cce 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -721,9 +721,11 @@ static void __init ic_bootp_init_ext(u8 *e)
 	*e++ = 3;		/* Default gateway request */
 	*e++ = 4;
 	e += 4;
+#if CONF_NAMESERVERS_MAX > 0
 	*e++ = 6;		/* (DNS) name server request */
-	*e++ = 8;
-	e += 8;
+	*e++ = 4 * CONF_NAMESERVERS_MAX;
+	e += 4 * CONF_NAMESERVERS_MAX;
+#endif
 	*e++ = 12;		/* Host name request */
 	*e++ = 32;
 	e += 32;
-- 
2.14.1

[PATCH 5/8] ipconfig: Document /proc/net/pnp

[Chris Novakovic]

Fully document the format used by the /proc/net/pnp file written by
ipconfig, explain where its values originate from, and clarify that the
tertiary name server IP and DNS domain name are only written to the file
when autoconfiguration is used.

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 Documentation/filesystems/nfs/nfsroot.txt | 34 ++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/Documentation/filesystems/nfs/nfsroot.txt b/Documentation/filesystems/nfs/nfsroot.txt
index 1513e5d663fd..a1030bea60d3 100644
--- a/Documentation/filesystems/nfs/nfsroot.txt
+++ b/Documentation/filesystems/nfs/nfsroot.txt
@@ -110,6 +110,9 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
 		will not be triggered if it is missing and NFS root is not
 		in operation.
 
+		Value is exported to /proc/net/pnp with the prefix "bootserver "
+		(see below).
+
 		Default: Determined using autoconfiguration.
 		         The address of the autoconfiguration server is used.
 
@@ -165,12 +168,33 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
 
                 Default: any
 
-  <dns0-ip>	IP address of first nameserver.
-		Value gets exported by /proc/net/pnp which is often linked
-		on embedded systems by /etc/resolv.conf.
+  <dns0-ip>	IP address of primary nameserver.
+		Value is exported to /proc/net/pnp with the prefix "nameserver "
+		(see below).
+
+		Default: None if not using autoconfiguration; determined
+		automatically if using autoconfiguration.
+
+  <dns1-ip>	IP address of secondary nameserver.
+		See <dns0-ip>.
+
+  After configuration (whether manual or automatic) is complete, a file is
+  created at /proc/net/pnp in the following format; lines are omitted if
+  their respective value is empty following configuration.
+
+	#PROTO: <DHCP|BOOTP|RARP|MANUAL>	(depending on configuration method)
+	domain <dns-domain>			(if autoconfigured, the DNS domain)
+	nameserver <dns0-ip>			(primary name server IP)
+	nameserver <dns1-ip>			(secondary name server IP)
+	nameserver <dns2-ip>			(tertiary name server IP)
+	bootserver <server-ip>			(NFS server IP)
+
+  <dns-domain> and <dns2-ip> are requested during autoconfiguration; they
+  cannot be specified as part of the "ip=" kernel command line parameter.
 
-  <dns1-ip>	IP address of second nameserver.
-		Same as above.
+  Because the "domain" and "nameserver" options are recognised by DNS
+  resolvers, /etc/resolv.conf is often linked to /proc/net/pnp on systems
+  that use an NFS root filesystem.
 
 
 nfsrootdebug
-- 
2.14.1

[PATCH 6/8] ipconfig: Correctly initialise ic_nameservers

[Chris Novakovic]

ic_nameservers, which stores the list of name servers discovered by
ipconfig, is initialised (i.e. has all of its elements set to NONE, or
0xffffffff) by ic_nameservers_predef() in the following scenarios:

 - before the "ip=" and "nfsaddrs=" kernel command line parameters are
   parsed (in ip_auto_config_setup());
 - before autoconfiguring via DHCP or BOOTP (in ic_bootp_init()), in
   order to clear any values that may have been set after parsing "ip="
   or "nfsaddrs=" and are no longer needed.

This means that ic_nameservers_predef() is not called when neither "ip="
nor "nfsaddrs=" is specified on the kernel command line. In this
scenario, every element in ic_nameservers remains set to 0x00000000,
which is indistinguishable from ANY and causes pnp_seq_show() to write
the following (bogus) information to /proc/net/pnp:

  #MANUAL
  nameserver 0.0.0.0
  nameserver 0.0.0.0
  nameserver 0.0.0.0

This is potentially problematic for systems that blindly link
/etc/resolv.conf to /proc/net/pnp.

Ensure that ic_nameservers is also initialised when neither "ip=" nor
"nfsaddrs=" is specified by calling ic_nameservers_predef() in
ip_auto_config(), but only when ip_auto_config_setup() was not called
earlier. This causes the following to be written to /proc/net/pnp, and
is consistent with what gets written when ipconfig is configured
manually but no name servers are specified on the kernel command line:

  #MANUAL

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 net/ipv4/ipconfig.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index 0f460d6d3cce..e11dfd29a929 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -750,6 +750,11 @@ static void __init ic_bootp_init_ext(u8 *e)
  */
 static inline void __init ic_bootp_init(void)
 {
+	/* Re-initialise all name servers to NONE, in case any were set via the
+	 * "ip=" or "nfsaddrs=" kernel command line parameters: any IP addresses
+	 * specified there will already have been decoded but are no longer
+	 * needed
+	 */
 	ic_nameservers_predef();
 
 	dev_add_pack(&bootp_packet_type);
@@ -1370,6 +1375,13 @@ static int __init ip_auto_config(void)
 	int err;
 	unsigned int i;
 
+	/* Initialise all name servers to NONE (but only if the "ip=" or
+	 * "nfsaddrs=" kernel command line parameters weren't decoded, otherwise
+	 * we'll overwrite the IP addresses specified there)
+	 */
+	if (ic_set_manually == 0)
+		ic_nameservers_predef();
+
 #ifdef CONFIG_PROC_FS
 	proc_create("pnp", 0444, init_net.proc_net, &pnp_seq_fops);
 #endif /* CONFIG_PROC_FS */
@@ -1593,6 +1605,7 @@ static int __init ip_auto_config_setup(char *addrs)
 		return 1;
 	}
 
+	/* Initialise all name servers to NONE */
 	ic_nameservers_predef();
 
 	/* Parse string for static IP assignment.  */
-- 
2.14.1

[PATCH 7/8] ipconfig: Write NTP server IPs to /proc/net/ntp

[Chris Novakovic]

Distributed filesystems are most effective when the server and client
clocks are synchronised. Embedded devices often use NFS for their
root filesystem but typically do not contain an RTC, so the clocks of
the NFS server and the embedded device will be out-of-sync when the root
filesystem is mounted (and may not be synchronised until late in the
boot process).

Extend ipconfig with the ability to export IP addresses of NTP servers
it discovers to /proc/net/ntp. They can be supplied as follows:

 - If ipconfig is configured manually via the "ip=" or "nfsaddrs="
   kernel command line parameters, one NTP server can be specified in
   the new "<ntp-ip>" parameter.
 - If ipconfig is autoconfigured via DHCP, request DHCP option 42 in
   the DHCPDISCOVER message, and record the IP addresses of up to three
   NTP servers sent by the responding DHCP server in the subsequent
   DHCPOFFER message.

ipconfig will only write the NTP server IP addresses it discovers to
/proc/net/ntp, one per line (in the order received from the DHCP server,
if DHCP autoconfiguration is used); making use of these NTP servers is
the responsibility of a user space process (e.g. an initrd/initram
script that invokes an NTP client before mounting an NFS root
filesystem).

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 Documentation/filesystems/nfs/nfsroot.txt | 35 +++++++++--
 net/ipv4/ipconfig.c                       | 99 ++++++++++++++++++++++++++++---
 2 files changed, 119 insertions(+), 15 deletions(-)

diff --git a/Documentation/filesystems/nfs/nfsroot.txt b/Documentation/filesystems/nfs/nfsroot.txt
index a1030bea60d3..4d55470f7ca9 100644
--- a/Documentation/filesystems/nfs/nfsroot.txt
+++ b/Documentation/filesystems/nfs/nfsroot.txt
@@ -5,6 +5,7 @@ Written 1996 by Gero Kuhlmann <gero@gkminix.han.de>
 Updated 1997 by Martin Mares <mj@atrey.karlin.mff.cuni.cz>
 Updated 2006 by Nico Schottelius <nico-kernel-nfsroot@schottelius.org>
 Updated 2006 by Horms <horms@verge.net.au>
+Updated 2018 by Chris Novakovic <chris@chrisn.me.uk>
 
 
 
@@ -79,7 +80,7 @@ nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
 
 
 ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
-   <dns0-ip>:<dns1-ip>
+   <dns0-ip>:<dns1-ip>:<nfs0-ip>
 
   This parameter tells the kernel how to configure IP addresses of devices
   and also how to set up the IP routing table. It was originally called
@@ -178,9 +179,18 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
   <dns1-ip>	IP address of secondary nameserver.
 		See <dns0-ip>.
 
-  After configuration (whether manual or automatic) is complete, a file is
-  created at /proc/net/pnp in the following format; lines are omitted if
-  their respective value is empty following configuration.
+  <ntp-ip>	IP address of a Network Time Protocol (NTP) server.
+		Value is exported to /proc/net/ntp, but is otherwise unused
+		(see below).
+
+		Default: None if not using autoconfiguration; determined
+		automatically if using autoconfiguration.
+
+  After configuration (whether manual or automatic) is complete, two files
+  are created in the following format; lines are omitted if their respective
+  value is empty following configuration:
+
+  - /proc/net/pnp:
 
 	#PROTO: <DHCP|BOOTP|RARP|MANUAL>	(depending on configuration method)
 	domain <dns-domain>			(if autoconfigured, the DNS domain)
@@ -189,13 +199,26 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
 	nameserver <dns2-ip>			(tertiary name server IP)
 	bootserver <server-ip>			(NFS server IP)
 
-  <dns-domain> and <dns2-ip> are requested during autoconfiguration; they
-  cannot be specified as part of the "ip=" kernel command line parameter.
+  - /proc/net/ntp:
+
+	<ntp0-ip>				(NTP server IP)
+	<ntp1-ip>				(NTP server IP)
+	<ntp2-ip>				(NTP server IP)
+
+  <dns-domain> and <dns2-ip> (in /proc/net/pnp) and <ntp1-ip> and <ntp2-ip>
+  (in /proc/net/ntp) are requested during autoconfiguration; they cannot be
+  specified as part of the "ip=" kernel command line parameter.
 
   Because the "domain" and "nameserver" options are recognised by DNS
   resolvers, /etc/resolv.conf is often linked to /proc/net/pnp on systems
   that use an NFS root filesystem.
 
+  Note that the kernel will not synchronise the system time with any NTP
+  servers it discovers; this is the responsibility of a user space process
+  (e.g. an initrd/initramfs script that passes the IP addresses listed in
+  /proc/net/ntp to an NTP client before mounting the real root filesystem
+  if it is on NFS).
+
 
 nfsrootdebug
 
diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index e11dfd29a929..a5d68e506494 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -28,6 +28,9 @@
  *
  *  Multiple Nameservers in /proc/net/pnp
  *              --  Josef Siemes <jsiemes@web.de>, Aug 2002
+ *
+ *  NTP servers in /proc/net/ntp
+ *              --  Chris Novakovic <chris@chrisn.me.uk>, April 2018
  */
 
 #include <linux/types.h>
@@ -93,6 +96,7 @@
 #define CONF_TIMEOUT_MAX	(HZ*30)	/* Maximum allowed timeout */
 #define CONF_NAMESERVERS_MAX   3       /* Maximum number of nameservers
 					   - '3' from resolv.h */
+#define CONF_NTP_SERVERS_MAX   3	/* Maximum number of NTP servers */
 
 #define NONE cpu_to_be32(INADDR_NONE)
 #define ANY cpu_to_be32(INADDR_ANY)
@@ -152,6 +156,7 @@ static int ic_proto_used;			/* Protocol used, if any */
 #define ic_proto_used 0
 #endif
 static __be32 ic_nameservers[CONF_NAMESERVERS_MAX]; /* DNS Server IP addresses */
+static __be32 ic_ntp_servers[CONF_NTP_SERVERS_MAX]; /* NTP server IP addresses */
 static u8 ic_domain[64];		/* DNS (not NIS) domain name */
 
 /*
@@ -576,6 +581,17 @@ static inline void __init ic_nameservers_predef(void)
 		ic_nameservers[i] = NONE;
 }
 
+/*
+ *  Predefine NTP servers
+ */
+static inline void __init ic_ntp_servers_predef(void)
+{
+	int i;
+
+	for (i = 0; i < CONF_NTP_SERVERS_MAX; i++)
+		ic_ntp_servers[i] = NONE;
+}
+
 /*
  *	DHCP/BOOTP support.
  */
@@ -671,6 +687,7 @@ ic_dhcp_init_options(u8 *options, struct ic_device *d)
 			17,	/* Boot path */
 			26,	/* MTU */
 			40,	/* NIS domain name */
+			42,	/* NTP servers */
 		};
 
 		*e++ = 55;	/* Parameter request list */
@@ -750,12 +767,13 @@ static void __init ic_bootp_init_ext(u8 *e)
  */
 static inline void __init ic_bootp_init(void)
 {
-	/* Re-initialise all name servers to NONE, in case any were set via the
-	 * "ip=" or "nfsaddrs=" kernel command line parameters: any IP addresses
-	 * specified there will already have been decoded but are no longer
-	 * needed
+	/* Re-initialise all name servers and NTP servers to NONE, in case any
+	 * were set via the "ip=" or "nfsaddrs=" kernel command line parameters:
+	 * any IP addresses specified there will already have been decoded but
+	 * are no longer needed
 	 */
 	ic_nameservers_predef();
+	ic_ntp_servers_predef();
 
 	dev_add_pack(&bootp_packet_type);
 }
@@ -919,6 +937,15 @@ static void __init ic_do_bootp_ext(u8 *ext)
 		ic_bootp_string(utsname()->domainname, ext+1, *ext,
 				__NEW_UTS_LEN);
 		break;
+	case 42:	/* NTP servers */
+		servers = *ext / 4;
+		if (servers > CONF_NTP_SERVERS_MAX)
+			servers = CONF_NTP_SERVERS_MAX;
+		for (i = 0; i < servers; i++) {
+			if (ic_ntp_servers[i] == NONE)
+				memcpy(&ic_ntp_servers[i], ext+1+4*i, 4);
+		}
+		break;
 	}
 }
 
@@ -1265,6 +1292,9 @@ static int __init ic_dynamic(void)
 
 #ifdef CONFIG_PROC_FS
 
+/*
+ *  Name servers:
+ */
 static int pnp_seq_show(struct seq_file *seq, void *v)
 {
 	int i;
@@ -1301,6 +1331,33 @@ static const struct file_operations pnp_seq_fops = {
 	.llseek		= seq_lseek,
 	.release	= single_release,
 };
+
+/*
+ *  NTP servers:
+ */
+static int ntp_seq_show(struct seq_file *seq, void *v)
+{
+	int i;
+
+	for (i = 0; i < CONF_NTP_SERVERS_MAX; i++) {
+		if (ic_ntp_servers[i] != NONE)
+			seq_printf(seq, "%pI4\n", &ic_ntp_servers[i]);
+	}
+	return 0;
+}
+
+static int ntp_seq_open(struct inode *indoe, struct file *file)
+{
+	return single_open(file, ntp_seq_show, NULL);
+}
+
+static const struct file_operations ntp_seq_fops = {
+	.open		= ntp_seq_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
 #endif /* CONFIG_PROC_FS */
 
 /*
@@ -1375,15 +1432,18 @@ static int __init ip_auto_config(void)
 	int err;
 	unsigned int i;
 
-	/* Initialise all name servers to NONE (but only if the "ip=" or
-	 * "nfsaddrs=" kernel command line parameters weren't decoded, otherwise
-	 * we'll overwrite the IP addresses specified there)
+	/* Initialise all name servers and NTP servers to NONE (but only if the
+	 * "ip=" or "nfsaddrs=" kernel command line parameters weren't decoded,
+	 * otherwise we'll overwrite the IP addresses specified there)
 	 */
-	if (ic_set_manually == 0)
+	if (ic_set_manually == 0) {
 		ic_nameservers_predef();
+		ic_ntp_servers_predef();
+	}
 
 #ifdef CONFIG_PROC_FS
 	proc_create("pnp", 0444, init_net.proc_net, &pnp_seq_fops);
+	proc_create("ntp", 0444, init_net.proc_net, &ntp_seq_fops);
 #endif /* CONFIG_PROC_FS */
 
 	if (!ic_enable)
@@ -1508,6 +1568,19 @@ static int __init ip_auto_config(void)
 		if (i + 1 == CONF_NAMESERVERS_MAX)
 			pr_cont("\n");
 	}
+	/* NTP servers (if any): */
+	for (i = 0; i < CONF_NTP_SERVERS_MAX; i++) {
+		if (ic_ntp_servers[i] != NONE) {
+			if (i == 0)
+				pr_info("     ntpserver%u=%pI4",
+					i, &ic_ntp_servers[i]);
+			else
+				pr_cont(", ntpserver%u=%pI4",
+					i, &ic_ntp_servers[i]);
+		}
+		if (i + 1 == CONF_NTP_SERVERS_MAX)
+			pr_cont("\n");
+	}
 #endif /* !SILENT */
 
 	/*
@@ -1605,8 +1678,9 @@ static int __init ip_auto_config_setup(char *addrs)
 		return 1;
 	}
 
-	/* Initialise all name servers to NONE */
+	/* Initialise all name servers and NTP servers to NONE */
 	ic_nameservers_predef();
+	ic_ntp_servers_predef();
 
 	/* Parse string for static IP assignment.  */
 	ip = addrs;
@@ -1665,6 +1739,13 @@ static int __init ip_auto_config_setup(char *addrs)
 						ic_nameservers[1] = NONE;
 				}
 				break;
+			case 9:
+				if (CONF_NTP_SERVERS_MAX >= 1) {
+					ic_ntp_servers[0] = in_aton(ip);
+					if (ic_ntp_servers[0] == ANY)
+						ic_ntp_servers[0] = NONE;
+				}
+				break;
 			}
 		}
 		ip = cp;
-- 
2.14.1

Re: [PATCH 7/8] ipconfig: Write NTP server IPs to /proc/net/ntp

[Chris Novakovic]

On 07/04/2018 05:09, Chris Novakovic wrote:
> Distributed filesystems are most effective when the server and client
> clocks are synchronised. Embedded devices often use NFS for their
> root filesystem but typically do not contain an RTC, so the clocks of
> the NFS server and the embedded device will be out-of-sync when the root
> filesystem is mounted (and may not be synchronised until late in the
> boot process).
> 
> Extend ipconfig with the ability to export IP addresses of NTP servers
> it discovers to /proc/net/ntp. They can be supplied as follows:
> 
>  - If ipconfig is configured manually via the "ip=" or "nfsaddrs="
>    kernel command line parameters, one NTP server can be specified in
>    the new "<ntp-ip>" parameter.
>  - If ipconfig is autoconfigured via DHCP, request DHCP option 42 in
>    the DHCPDISCOVER message, and record the IP addresses of up to three
>    NTP servers sent by the responding DHCP server in the subsequent
>    DHCPOFFER message.
> 
> ipconfig will only write the NTP server IP addresses it discovers to
> /proc/net/ntp, one per line (in the order received from the DHCP server,
> if DHCP autoconfiguration is used); making use of these NTP servers is
> the responsibility of a user space process (e.g. an initrd/initram
> script that invokes an NTP client before mounting an NFS root
> filesystem).
> 
> Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>

Sorry, I just spotted a minor typo in the commit message and
documentation in this patch --- I'll send a v2 shortly.

[PATCH v2 7/8] ipconfig: Write NTP server IPs to /proc/net/ntp

[Chris Novakovic]

Distributed filesystems are most effective when the server and client
clocks are synchronised. Embedded devices often use NFS for their
root filesystem but typically do not contain an RTC, so the clocks of
the NFS server and the embedded device will be out-of-sync when the root
filesystem is mounted (and may not be synchronised until late in the
boot process).

Extend ipconfig with the ability to export IP addresses of NTP servers
it discovers to /proc/net/ntp. They can be supplied as follows:

 - If ipconfig is configured manually via the "ip=" or "nfsaddrs="
   kernel command line parameters, one NTP server can be specified in
   the new "<ntp0-ip>" parameter.
 - If ipconfig is autoconfigured via DHCP, request DHCP option 42 in
   the DHCPDISCOVER message, and record the IP addresses of up to three
   NTP servers sent by the responding DHCP server in the subsequent
   DHCPOFFER message.

ipconfig will only write the NTP server IP addresses it discovers to
/proc/net/ntp, one per line (in the order received from the DHCP server,
if DHCP autoconfiguration is used); making use of these NTP servers is
the responsibility of a user space process (e.g. an initrd/initram
script that invokes an NTP client before mounting an NFS root
filesystem).

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 Documentation/filesystems/nfs/nfsroot.txt | 35 +++++++++--
 net/ipv4/ipconfig.c                       | 99 ++++++++++++++++++++++++++++---
 2 files changed, 119 insertions(+), 15 deletions(-)

diff --git a/Documentation/filesystems/nfs/nfsroot.txt b/Documentation/filesystems/nfs/nfsroot.txt
index a1030bea60d3..8e51c1a39564 100644
--- a/Documentation/filesystems/nfs/nfsroot.txt
+++ b/Documentation/filesystems/nfs/nfsroot.txt
@@ -5,6 +5,7 @@ Written 1996 by Gero Kuhlmann <gero@gkminix.han.de>
 Updated 1997 by Martin Mares <mj@atrey.karlin.mff.cuni.cz>
 Updated 2006 by Nico Schottelius <nico-kernel-nfsroot@schottelius.org>
 Updated 2006 by Horms <horms@verge.net.au>
+Updated 2018 by Chris Novakovic <chris@chrisn.me.uk>
 
 
 
@@ -79,7 +80,7 @@ nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
 
 
 ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
-   <dns0-ip>:<dns1-ip>
+   <dns0-ip>:<dns1-ip>:<ntp0-ip>
 
   This parameter tells the kernel how to configure IP addresses of devices
   and also how to set up the IP routing table. It was originally called
@@ -178,9 +179,18 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
   <dns1-ip>	IP address of secondary nameserver.
 		See <dns0-ip>.
 
-  After configuration (whether manual or automatic) is complete, a file is
-  created at /proc/net/pnp in the following format; lines are omitted if
-  their respective value is empty following configuration.
+  <ntp0-ip>	IP address of a Network Time Protocol (NTP) server.
+		Value is exported to /proc/net/ntp, but is otherwise unused
+		(see below).
+
+		Default: None if not using autoconfiguration; determined
+		automatically if using autoconfiguration.
+
+  After configuration (whether manual or automatic) is complete, two files
+  are created in the following format; lines are omitted if their respective
+  value is empty following configuration:
+
+  - /proc/net/pnp:
 
 	#PROTO: <DHCP|BOOTP|RARP|MANUAL>	(depending on configuration method)
 	domain <dns-domain>			(if autoconfigured, the DNS domain)
@@ -189,13 +199,26 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
 	nameserver <dns2-ip>			(tertiary name server IP)
 	bootserver <server-ip>			(NFS server IP)
 
-  <dns-domain> and <dns2-ip> are requested during autoconfiguration; they
-  cannot be specified as part of the "ip=" kernel command line parameter.
+  - /proc/net/ntp:
+
+	<ntp0-ip>				(NTP server IP)
+	<ntp1-ip>				(NTP server IP)
+	<ntp2-ip>				(NTP server IP)
+
+  <dns-domain> and <dns2-ip> (in /proc/net/pnp) and <ntp1-ip> and <ntp2-ip>
+  (in /proc/net/ntp) are requested during autoconfiguration; they cannot be
+  specified as part of the "ip=" kernel command line parameter.
 
   Because the "domain" and "nameserver" options are recognised by DNS
   resolvers, /etc/resolv.conf is often linked to /proc/net/pnp on systems
   that use an NFS root filesystem.
 
+  Note that the kernel will not synchronise the system time with any NTP
+  servers it discovers; this is the responsibility of a user space process
+  (e.g. an initrd/initramfs script that passes the IP addresses listed in
+  /proc/net/ntp to an NTP client before mounting the real root filesystem
+  if it is on NFS).
+
 
 nfsrootdebug
 
diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index e11dfd29a929..a5d68e506494 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -28,6 +28,9 @@
  *
  *  Multiple Nameservers in /proc/net/pnp
  *              --  Josef Siemes <jsiemes@web.de>, Aug 2002
+ *
+ *  NTP servers in /proc/net/ntp
+ *              --  Chris Novakovic <chris@chrisn.me.uk>, April 2018
  */
 
 #include <linux/types.h>
@@ -93,6 +96,7 @@
 #define CONF_TIMEOUT_MAX	(HZ*30)	/* Maximum allowed timeout */
 #define CONF_NAMESERVERS_MAX   3       /* Maximum number of nameservers
 					   - '3' from resolv.h */
+#define CONF_NTP_SERVERS_MAX   3	/* Maximum number of NTP servers */
 
 #define NONE cpu_to_be32(INADDR_NONE)
 #define ANY cpu_to_be32(INADDR_ANY)
@@ -152,6 +156,7 @@ static int ic_proto_used;			/* Protocol used, if any */
 #define ic_proto_used 0
 #endif
 static __be32 ic_nameservers[CONF_NAMESERVERS_MAX]; /* DNS Server IP addresses */
+static __be32 ic_ntp_servers[CONF_NTP_SERVERS_MAX]; /* NTP server IP addresses */
 static u8 ic_domain[64];		/* DNS (not NIS) domain name */
 
 /*
@@ -576,6 +581,17 @@ static inline void __init ic_nameservers_predef(void)
 		ic_nameservers[i] = NONE;
 }
 
+/*
+ *  Predefine NTP servers
+ */
+static inline void __init ic_ntp_servers_predef(void)
+{
+	int i;
+
+	for (i = 0; i < CONF_NTP_SERVERS_MAX; i++)
+		ic_ntp_servers[i] = NONE;
+}
+
 /*
  *	DHCP/BOOTP support.
  */
@@ -671,6 +687,7 @@ ic_dhcp_init_options(u8 *options, struct ic_device *d)
 			17,	/* Boot path */
 			26,	/* MTU */
 			40,	/* NIS domain name */
+			42,	/* NTP servers */
 		};
 
 		*e++ = 55;	/* Parameter request list */
@@ -750,12 +767,13 @@ static void __init ic_bootp_init_ext(u8 *e)
  */
 static inline void __init ic_bootp_init(void)
 {
-	/* Re-initialise all name servers to NONE, in case any were set via the
-	 * "ip=" or "nfsaddrs=" kernel command line parameters: any IP addresses
-	 * specified there will already have been decoded but are no longer
-	 * needed
+	/* Re-initialise all name servers and NTP servers to NONE, in case any
+	 * were set via the "ip=" or "nfsaddrs=" kernel command line parameters:
+	 * any IP addresses specified there will already have been decoded but
+	 * are no longer needed
 	 */
 	ic_nameservers_predef();
+	ic_ntp_servers_predef();
 
 	dev_add_pack(&bootp_packet_type);
 }
@@ -919,6 +937,15 @@ static void __init ic_do_bootp_ext(u8 *ext)
 		ic_bootp_string(utsname()->domainname, ext+1, *ext,
 				__NEW_UTS_LEN);
 		break;
+	case 42:	/* NTP servers */
+		servers = *ext / 4;
+		if (servers > CONF_NTP_SERVERS_MAX)
+			servers = CONF_NTP_SERVERS_MAX;
+		for (i = 0; i < servers; i++) {
+			if (ic_ntp_servers[i] == NONE)
+				memcpy(&ic_ntp_servers[i], ext+1+4*i, 4);
+		}
+		break;
 	}
 }
 
@@ -1265,6 +1292,9 @@ static int __init ic_dynamic(void)
 
 #ifdef CONFIG_PROC_FS
 
+/*
+ *  Name servers:
+ */
 static int pnp_seq_show(struct seq_file *seq, void *v)
 {
 	int i;
@@ -1301,6 +1331,33 @@ static const struct file_operations pnp_seq_fops = {
 	.llseek		= seq_lseek,
 	.release	= single_release,
 };
+
+/*
+ *  NTP servers:
+ */
+static int ntp_seq_show(struct seq_file *seq, void *v)
+{
+	int i;
+
+	for (i = 0; i < CONF_NTP_SERVERS_MAX; i++) {
+		if (ic_ntp_servers[i] != NONE)
+			seq_printf(seq, "%pI4\n", &ic_ntp_servers[i]);
+	}
+	return 0;
+}
+
+static int ntp_seq_open(struct inode *indoe, struct file *file)
+{
+	return single_open(file, ntp_seq_show, NULL);
+}
+
+static const struct file_operations ntp_seq_fops = {
+	.open		= ntp_seq_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
 #endif /* CONFIG_PROC_FS */
 
 /*
@@ -1375,15 +1432,18 @@ static int __init ip_auto_config(void)
 	int err;
 	unsigned int i;
 
-	/* Initialise all name servers to NONE (but only if the "ip=" or
-	 * "nfsaddrs=" kernel command line parameters weren't decoded, otherwise
-	 * we'll overwrite the IP addresses specified there)
+	/* Initialise all name servers and NTP servers to NONE (but only if the
+	 * "ip=" or "nfsaddrs=" kernel command line parameters weren't decoded,
+	 * otherwise we'll overwrite the IP addresses specified there)
 	 */
-	if (ic_set_manually == 0)
+	if (ic_set_manually == 0) {
 		ic_nameservers_predef();
+		ic_ntp_servers_predef();
+	}
 
 #ifdef CONFIG_PROC_FS
 	proc_create("pnp", 0444, init_net.proc_net, &pnp_seq_fops);
+	proc_create("ntp", 0444, init_net.proc_net, &ntp_seq_fops);
 #endif /* CONFIG_PROC_FS */
 
 	if (!ic_enable)
@@ -1508,6 +1568,19 @@ static int __init ip_auto_config(void)
 		if (i + 1 == CONF_NAMESERVERS_MAX)
 			pr_cont("\n");
 	}
+	/* NTP servers (if any): */
+	for (i = 0; i < CONF_NTP_SERVERS_MAX; i++) {
+		if (ic_ntp_servers[i] != NONE) {
+			if (i == 0)
+				pr_info("     ntpserver%u=%pI4",
+					i, &ic_ntp_servers[i]);
+			else
+				pr_cont(", ntpserver%u=%pI4",
+					i, &ic_ntp_servers[i]);
+		}
+		if (i + 1 == CONF_NTP_SERVERS_MAX)
+			pr_cont("\n");
+	}
 #endif /* !SILENT */
 
 	/*
@@ -1605,8 +1678,9 @@ static int __init ip_auto_config_setup(char *addrs)
 		return 1;
 	}
 
-	/* Initialise all name servers to NONE */
+	/* Initialise all name servers and NTP servers to NONE */
 	ic_nameservers_predef();
+	ic_ntp_servers_predef();
 
 	/* Parse string for static IP assignment.  */
 	ip = addrs;
@@ -1665,6 +1739,13 @@ static int __init ip_auto_config_setup(char *addrs)
 						ic_nameservers[1] = NONE;
 				}
 				break;
+			case 9:
+				if (CONF_NTP_SERVERS_MAX >= 1) {
+					ic_ntp_servers[0] = in_aton(ip);
+					if (ic_ntp_servers[0] == ANY)
+						ic_ntp_servers[0] = NONE;
+				}
+				break;
 			}
 		}
 		ip = cp;
-- 
2.14.1

[PATCH 8/8] CREDITS: Add Chris Novakovic

[Chris Novakovic]

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 CREDITS | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CREDITS b/CREDITS
index 989cda91c427..5a13bf62c569 100644
--- a/CREDITS
+++ b/CREDITS
@@ -2765,6 +2765,10 @@ E: noring@nocrew.org
 W: http://www.lysator.liu.se/~noring/
 D: dsp56k device driver
 
+N: Chris Novakovic
+E: chris@chrisn.me.uk
+D: ipconfig: NTP server support, bug fixes, documentation
+
 N: Michael O'Reilly
 E: michael@iinet.com.au
 E: oreillym@tartarus.uwa.edu.au
-- 
2.14.1

Re: [PATCH 0/8] ipconfig: NTP server support, bug fixes, documentation improvements

[David Miller]

From: Chris Novakovic <chris@chrisn.me.uk>
Date: Sat,  7 Apr 2018 05:08:55 +0100

> This series (against net-next) makes various improvements to ipconfig:

The net-next tree is closed at this time, please resubmit this series
when that tree opens up again.

Thank you.

Re: [PATCH 0/8] ipconfig: NTP server support, bug fixes, documentation improvements

[Chris Novakovic]

On 07/04/2018 17:29, David Miller wrote:
> From: Chris Novakovic <chris@chrisn.me.uk>
> Date: Sat,  7 Apr 2018 05:08:55 +0100
> 
>> This series (against net-next) makes various improvements to ipconfig:
> 
> The net-next tree is closed at this time, please resubmit this series
> when that tree opens up again.
> 
> Thank you.

Will do --- apologies for the noise.

[PATCH 0/8] ipconfig: NTP server support, bug fixes, documentation improvements

[Chris Novakovic]

This series (against net-next) makes various improvements to ipconfig.
It was mistakenly posted on 2018-04-07, while net-next was closed; it
still applies cleanly.

 - Patch #1 correctly documents the behaviour of parameter 4 in the
   "ip=" and "nfsaddrs=" command line parameter.
 - Patch #2 tidies up the printk()s for reporting configured name
   servers.
 - Patch #3 fixes a bug in autoconfiguration via BOOTP whereby the IP
   addresses of IEN-116 name servers are requested from the BOOTP
   server, rather than those of DNS name servers.
 - Patch #4 requests the number of DNS servers specified by
   CONF_NAMESERVERS_MAX when autoconfiguring via BOOTP, rather than
   hardcoding it to 2.
 - Patch #5 fully documents the contents and format of /proc/net/pnp in
   Documentation/filesystems/nfs/nfsroot.txt.
 - Patch #6 fixes a bug whereby bogus information is written to
   /proc/net/pnp when ipconfig is not used.
 - Patch #7 allows for NTP servers to be configured (manually on the
   kernel command line or automatically via DHCP), enabling systems with
   an NFS root filesystem to synchronise their clock before mounting
   their root filesystem.

Chris Novakovic (8):
  ipconfig: Document setting of NIS domain name
  ipconfig: Tidy up reporting of name servers
  ipconfig: BOOTP: Don't request IEN-116 name servers
  ipconfig: BOOTP: Request CONF_NAMESERVERS_MAX name servers
  ipconfig: Document /proc/net/pnp
  ipconfig: Correctly initialise ic_nameservers
  ipconfig: Write NTP server IPs to /proc/net/ntp
  CREDITS: Add Chris Novakovic

 CREDITS                                   |   4 +
 Documentation/filesystems/nfs/nfsroot.txt |  70 ++++++++++++++---
 net/ipv4/ipconfig.c                       | 121 +++++++++++++++++++++++++++---
 3 files changed, 174 insertions(+), 21 deletions(-)

-- 
2.14.1

[PATCH 6/8] ipconfig: Correctly initialise ic_nameservers

[Chris Novakovic]

ic_nameservers, which stores the list of name servers discovered by
ipconfig, is initialised (i.e. has all of its elements set to NONE, or
0xffffffff) by ic_nameservers_predef() in the following scenarios:

 - before the "ip=" and "nfsaddrs=" kernel command line parameters are
   parsed (in ip_auto_config_setup());
 - before autoconfiguring via DHCP or BOOTP (in ic_bootp_init()), in
   order to clear any values that may have been set after parsing "ip="
   or "nfsaddrs=" and are no longer needed.

This means that ic_nameservers_predef() is not called when neither "ip="
nor "nfsaddrs=" is specified on the kernel command line. In this
scenario, every element in ic_nameservers remains set to 0x00000000,
which is indistinguishable from ANY and causes pnp_seq_show() to write
the following (bogus) information to /proc/net/pnp:

  #MANUAL
  nameserver 0.0.0.0
  nameserver 0.0.0.0
  nameserver 0.0.0.0

This is potentially problematic for systems that blindly link
/etc/resolv.conf to /proc/net/pnp.

Ensure that ic_nameservers is also initialised when neither "ip=" nor
"nfsaddrs=" are specified by calling ic_nameservers_predef() in
ip_auto_config(), but only when ip_auto_config_setup() was not called
earlier. This causes the following to be written to /proc/net/pnp, and
is consistent with what gets written when ipconfig is configured
manually but no name servers are specified on the kernel command line:

  #MANUAL

Signed-off-by: Chris Novakovic <chris@chrisn.me.uk>
---
 net/ipv4/ipconfig.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index 0f460d6d3cce..e11dfd29a929 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -750,6 +750,11 @@ static void __init ic_bootp_init_ext(u8 *e)
  */
 static inline void __init ic_bootp_init(void)
 {
+	/* Re-initialise all name servers to NONE, in case any were set via the
+	 * "ip=" or "nfsaddrs=" kernel command line parameters: any IP addresses
+	 * specified there will already have been decoded but are no longer
+	 * needed
+	 */
 	ic_nameservers_predef();
 
 	dev_add_pack(&bootp_packet_type);
@@ -1370,6 +1375,13 @@ static int __init ip_auto_config(void)
 	int err;
 	unsigned int i;
 
+	/* Initialise all name servers to NONE (but only if the "ip=" or
+	 * "nfsaddrs=" kernel command line parameters weren't decoded, otherwise
+	 * we'll overwrite the IP addresses specified there)
+	 */
+	if (ic_set_manually == 0)
+		ic_nameservers_predef();
+
 #ifdef CONFIG_PROC_FS
 	proc_create("pnp", 0444, init_net.proc_net, &pnp_seq_fops);
 #endif /* CONFIG_PROC_FS */
@@ -1593,6 +1605,7 @@ static int __init ip_auto_config_setup(char *addrs)
 		return 1;
 	}
 
+	/* Initialise all name servers to NONE */
 	ic_nameservers_predef();
 
 	/* Parse string for static IP assignment.  */
-- 
2.14.1