Re: patch: support long (above 14 bytes) HW addresses in arp_ioctl

From: Constantine Gavrilov
Date: Mon Nov 03 2008 - 11:36:34 EST

Updated version of the patch uses MAX_ADDR_LEN from netdevice.h as the maximal length of MAC address.

Constantine Gavrilov wrote:
While working with OFED infiniband stack that uses 20 byte long HW addresses for IP over IB, I have paid attention to the following arp_ioctl problem.

The ioctl uses a data structure that limits a length of HW address to 14 bytes. The IP stack and the arp cache code do not have that limitation. This leads to the following problems:

* arp_ioctl cannot be used to set, get, or delete arp entries for those adapters that have HW addresses longer than 14 bytes
* arp_ioctl will corrupt the kernel and user memory when this ioctl is used on the adapters that have HW addresses longer that 14 bytes. This is because when copying the HW address, the arp_ioctl code copies dev->addr_len bytes without checking that addr_len is not above 14 bytes. This is done both for copy_to_user() and memcpy() calls on kernel data structures allocated on stack. The memcpy() call in particular, will corrupt kernel stack.

Attached please find the patch that fixes both problems. In addition, the patch changes the maximal number of bytes for HW address that will be seen in /proc/net/arp from ~10 to ~30. Without the last change, output of /proc/net/arp truncates the the large MAC entries, which makes the arp utility useless.

The patch does not change the existing ABI but extends it. The kernel structure used in arp_ioctl calls is changed to support larger addresses, while the user-space structure is extended by appending extra-space to the end of the structure if ATF_NEWARPCTL -- a new flag -- is set in arp_flags of existing user-space structure. This allows avoiding big changes to the existing code while preserving the ABI compatibility.


--
----------------------------------------
Constantine Gavrilov
Kernel Developer
Platform Group
XIV, an IBM global brand 1 Azrieli Center, Tel-Aviv
Phone: +972-3-6074672
Fax: +972-3-6959749
----------------------------------------


--- include/linux/if_arp.h.orig 2008-10-10 00:13:53.000000000 +0200
+++ include/linux/if_arp.h 2008-11-03 18:29:14.000000000 +0200
@@ -99,14 +99,27 @@
#define ARPOP_InREPLY 9 /* InARP reply */
#define ARPOP_NAK 10 /* (ATM)ARP NAK */

+struct hwaddr {
+ sa_family_t sa_family; /* address family, AF_xxx */
+ char sa_data[MAX_ADDR_LEN]; /* 32 bytes of HW address */
+};

/* ARP ioctl request. */
struct arpreq {
struct sockaddr arp_pa; /* protocol address */
+ struct hwaddr arp_ha; /* hardware address */
+ int arp_flags; /* flags */
+ struct sockaddr arp_netmask; /* netmask (only for proxy arps) */
+ char arp_dev[16];
+};
+
+struct arpreq_user {
+ struct sockaddr arp_pa; /* protocol address */
struct sockaddr arp_ha; /* hardware address */
int arp_flags; /* flags */
struct sockaddr arp_netmask; /* netmask (only for proxy arps) */
char arp_dev[16];
+ char arp_ha_ext[MAX_ADDR_LEN-14]; /* extended part of HW address */
};

struct arpreq_old {
@@ -124,6 +137,10 @@
#define ATF_NETMASK 0x20 /* want to use a netmask (only
for proxy entries) */
#define ATF_DONTPUB 0x40 /* don't answer this addresses */
+#define ATF_NEWARPCTL 0x80 /* use larger buff for hw address */
+
+#define NOT_VALID_ARP_CTL(__dev, __r) ((__dev->addr_len > sizeof(((struct arpreq_user *)__r)->arp_ha.sa_data)) && \
+ ((__dev->addr_len > sizeof(__r->arp_ha.sa_data)) || !(__r->arp_flags & ATF_NEWARPCTL)))

/*
* This structure defines an ethernet arp header.
--- net/ipv4/arp.c.orig 2008-10-10 00:13:53.000000000 +0200
+++ net/ipv4/arp.c 2008-11-02 16:59:34.000000000 +0200
@@ -968,7 +968,12 @@
if (!dev && (r->arp_flags & ATF_COM)) {
dev = dev_getbyhwaddr(net, r->arp_ha.sa_family,
r->arp_ha.sa_data);
- if (!dev)
+ if (!dev || NOT_VALID_ARP_CTL(dev, r)) /*
+ if we managed to find an interface that should have
+ larger buffer for HW MAC than one that was supposedly supplied,
+ it is not our interface -- the NIC was matched by "junk"
+ extended data in r and not by user supplied address
+ */
return -ENODEV;
}
if (mask) {
@@ -1004,6 +1009,9 @@
if (!dev)
return -EINVAL;
}
+ if(NOT_VALID_ARP_CTL(dev, r))
+ return -EINVAL; /* the user gave too short HW address */
+
switch (dev->type) {
#ifdef CONFIG_FDDI
case ARPHRD_FDDI:
@@ -1127,11 +1135,23 @@
* Handle an ARP layer I/O control request.
*/

+#define swap_arp_ioctl_structs(__in, __out) \
+do {\
+ __out.arp_pa = __in.arp_pa; \
+ __out.arp_ha.sa_family = __in.arp_ha.sa_family; \
+ memcpy(&__out.arp_ha.sa_data[0], &__in.arp_ha.sa_data[0], sizeof(__in.arp_ha.sa_data)); \
+ __out.arp_flags = __in.arp_flags; \
+ __out.arp_netmask = __in.arp_netmask; \
+ memcpy(&__out.arp_dev[0], &__in.arp_dev[0], sizeof(__in.arp_dev)); \
+} while(0)
+
int arp_ioctl(struct net *net, unsigned int cmd, void __user *arg)
{
int err;
struct arpreq r;
+ struct arpreq_user user_r;
struct net_device *dev = NULL;
+ int is_newarpctl = 0;

switch (cmd) {
case SIOCDARP:
@@ -1139,9 +1159,16 @@
if (!capable(CAP_NET_ADMIN))
return -EPERM;
case SIOCGARP:
- err = copy_from_user(&r, arg, sizeof(struct arpreq));
+ err = copy_from_user(&user_r, arg, offsetof(struct arpreq_user, arp_ha_ext));
if (err)
return -EFAULT;
+ swap_arp_ioctl_structs(user_r, r);
+ if(user_r.arp_flags & ATF_NEWARPCTL) {
+ is_newarpctl = 1;
+ err = copy_from_user(&r.arp_ha.sa_data[0] + sizeof(user_r.arp_ha.sa_data), (char *)arg + offsetof(struct arpreq_user, arp_ha_ext), sizeof(user_r.arp_ha_ext));
+ if (err)
+ return -EFAULT;
+ }
break;
default:
return -EINVAL;
@@ -1175,15 +1202,35 @@

switch (cmd) {
case SIOCDARP:
+ /* Delete arp does not use the value of HW address, we do not have to check whether the supplied buffer is large enough */
err = arp_req_delete(net, &r, dev);
break;
case SIOCSARP:
+ /* Our HW addr buffer may be not large enough */
+ /* Check the case when the interface was found by a given name and let arp_req_set to check for other cases */
+ if(dev && NOT_VALID_ARP_CTL(dev, (&r))) {
+ err = -EINVAL; /* the user gave truncated HW address */
+ goto out;
+ }
err = arp_req_set(net, &r, dev);
break;
case SIOCGARP:
- err = arp_req_get(&r, dev);
- if (!err && copy_to_user(arg, &r, sizeof(r)))
- err = -EFAULT;
+ if(NOT_VALID_ARP_CTL(dev, (&r))) {
+ err = -EINVAL; /* the user has not given enough place to store HW address */
+ goto out;
+ }
+ memset(&r.arp_ha.sa_data[0], 0, sizeof(r.arp_ha.sa_data));
+ err = arp_req_get(&r, dev);
+ if (!err) {
+ swap_arp_ioctl_structs(r, user_r);
+ if(is_newarpctl) {
+ memcpy(&user_r.arp_ha_ext[0], &r.arp_ha.sa_data[0]+sizeof(user_r.arp_ha.sa_data), sizeof(user_r.arp_ha_ext));
+ err = copy_to_user(arg, &user_r, sizeof(user_r));
+ } else
+ err = copy_to_user(arg, &user_r, offsetof(struct arpreq_user, arp_ha_ext));
+ if (err)
+ err = -EFAULT;
+ }
break;
}
out:
@@ -1281,7 +1328,7 @@
}
#endif /* CONFIG_AX25 */

-#define HBUFFERLEN 30
+#define HBUFFERLEN 96

static void arp_format_neigh_entry(struct seq_file *seq,
struct neighbour *n)

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