netdev - [PATCH 6/8] ipconfig: Correctly initialise ic

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Message-Id: <20180407040903.8997-7-chris@chrisn.me.uk>
Date:   Sat,  7 Apr 2018 05:09:01 +0100
From:   Chris Novakovic <chris@...isn.me.uk>
To:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     Chris Novakovic <chris@...isn.me.uk>
Subject: [PATCH 6/8] ipconfig: Correctly initialise ic_nameservers

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@...isn.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