[PATCH 3.18 56/85] ipconfig: Correctly initialise ic_nameservers

Greg Kroah-Hartman
2018-08-07T18:58:49Z

From: Chris Novakovic <chris@chrisn.me.uk>

[ Upstream commit 300eec7c0a2495f771709c7642aa15f7cc148b83 ]

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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/ipconfig.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -772,6 +772,11 @@ static void __init ic_bootp_init_ext(u8
*/
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);
@@ -1404,6 +1409,13 @@ 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", S_IRUGO, init_net.proc_net, &pnp_seq_fops);
#endif /* CONFIG_PROC_FS */
@@ -1605,6 +1617,7 @@ static int __init ip_auto_config_setup(c
return 1;
}

+ /* Initialise all name servers to NONE */
ic_nameservers_predef();

/* Parse string for static IP assignment. */