[PATCH 4.9 014/108] NET: Fix /proc/net/arp for AX.25

Greg Kroah-Hartman
2017-06-15T17:57:11Z

From: Ralf Baechle <ralf@linux-mips.org>

[ Upstream commit 4872e57c812dd312bf8193b5933fa60585cda42f ]

When sending ARP requests over AX.25 links the hwaddress in the neighbour
cache are not getting initialized. For such an incomplete arp entry
ax2asc2 will generate an empty string resulting in /proc/net/arp output
like the following:

$ cat /proc/net/arp
IP address HW type Flags HW address Mask Device
192.168.122.1 0x1 0x2 52:54:00:00:5d:5f * ens3
172.20.1.99 0x3 0x0 * bpq0

The missing field will confuse the procfs parsing of arp(8) resulting in
incorrect output for the device such as the following:

$ arp
Address HWtype HWaddress Flags Mask Iface
gateway ether 52:54:00:00:5d:5f C ens3
172.20.1.99 (incomplete) ens3

This changes the content of /proc/net/arp to:

$ cat /proc/net/arp
IP address HW type Flags HW address Mask Device
172.20.1.99 0x3 0x0 * * bpq0
192.168.122.1 0x1 0x2 52:54:00:00:5d:5f * ens3

To do so it change ax2asc to put the string "*" in buf for a NULL address
argument. Finally the HW address field is left aligned in a 17 character
field (the length of an ethernet HW address in the usual hex notation) for
readability.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/arp.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -1263,7 +1263,7 @@ void __init arp_init(void)
/*
* ax25 -> ASCII conversion
*/
-static char *ax2asc2(ax25_address *a, char *buf)
+static void ax2asc2(ax25_address *a, char *buf)
{
char c, *s;
int n;
@@ -1285,10 +1285,10 @@ static char *ax2asc2(ax25_address *a, ch
*s++ = n + '0';
*s++ = '\0';

- if (*buf == '\0' || *buf == '-')
- return "*";
-
- return buf;
+ if (*buf == '\0' || *buf == '-') {
+ buf[0] = '*';
+ buf[1] = '\0';
+ }
}
#endif /* CONFIG_AX25 */

@@ -1322,7 +1322,7 @@ static void arp_format_neigh_entry(struc
}
#endif
sprintf(tbuf, "%pI4", n->primary_key);
- seq_printf(seq, "%-16s 0x%-10x0x%-10x%s * %s\n",
+ seq_printf(seq, "%-16s 0x%-10x0x%-10x%-17s * %s\n",
tbuf, hatype, arp_state_to_flags(n), hbuffer, dev->name);
read_unlock(&n->lock);
}