Commit bd89efc5 authored May 12, 2006 by Simon Kelley Committed by David S. Miller May 12, 2006

[NEIGH]: Fix IP-over-ATM and ARP interaction.



The classical IP over ATM code maintains its own IPv4 <-> <ATM stuff>
ARP table, using the standard neighbour-table code. The
neigh_table_init function adds this neighbour table to a linked list
of all neighbor tables which is used by the functions neigh_delete()
neigh_add() and neightbl_set(), all called by the netlink code.

Once the ATM neighbour table is added to the list, there are two
tables with family == AF_INET there, and ARP entries sent via netlink
go into the first table with matching family. This is indeterminate
and often wrong.

To see the bug, on a kernel with CLIP enabled, create a standard IPv4
ARP entry by pinging an unused address on a local subnet. Then attempt
to complete that entry by doing

ip neigh replace <ip address> lladdr <some mac address> nud reachable

Looking at the ARP tables by using 

ip neigh show

will reveal two ARP entries for the same address. One of these can be
found in /proc/net/arp, and the other in /proc/net/atm/arp.

This patch adds a new function, neigh_table_init_no_netlink() which
does everything the neigh_table_init() does, except add the table to
the netlink all-arp-tables chain. In addition neigh_table_init() has a
check that all tables on the chain have a distinct address family.
The init call in clip.c is changed to call
neigh_table_init_no_netlink().

Since ATM ARP tables are rather more complicated than can currently be
handled by the available rtattrs in the netlink protocol, no
functionality is lost by this patch, and non-ATM ARP manipulation via
netlink is rescued. A more complete solution would involve a rtattr
for ATM ARP entries and some way for the netlink code to give
neigh_add and friends more information than just address family with
which to find the correct ARP table.

[ I've changed the assertion checking in neigh_table_init() to not
  use BUG_ON() while holding neigh_tbl_lock.  Instead we remember that
  we found an existing tbl with the same family, and after dropping
  the lock we'll give a diagnostic kernel log message and a stack dump.
  -DaveM ]

Signed-off-by: Simon Kelley <simon@thekelleys.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent ef348144

include/net/neighbour.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -211,6 +211,7 @@ struct neigh_table
		#define NEIGH_UPDATE_F_ADMIN 0x80000000

		extern void neigh_table_init(struct neigh_table *tbl);
		extern void neigh_table_init_no_netlink(struct neigh_table *tbl);
		extern int neigh_table_clear(struct neigh_table *tbl);
		extern struct neighbour * neigh_lookup(struct neigh_table *tbl,
		const void *pkey,

net/atm/clip.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -963,7 +963,7 @@ static struct file_operations arp_seq_fops = {
		static int __init atm_clip_init(void)
		{
		struct proc_dir_entry *p;
		neigh_table_init(&clip_tbl);
		neigh_table_init_no_netlink(&clip_tbl);

		clip_tbl_hook = &clip_tbl;
		register_atm_ioctl(&clip_ioctl_ops);

net/core/neighbour.c

+19 −2

Original line number	Diff line number	Diff line
		@@ -1326,8 +1326,7 @@ void neigh_parms_destroy(struct neigh_parms *parms)
		kfree(parms);
		}


		void neigh_table_init(struct neigh_table *tbl)
		void neigh_table_init_no_netlink(struct neigh_table *tbl)
		{
		unsigned long now = jiffies;
		unsigned long phsize;
		@@ -1383,10 +1382,27 @@ void neigh_table_init(struct neigh_table *tbl)

		tbl->last_flush = now;
		tbl->last_rand = now + tbl->parms.reachable_time * 20;
		}

		void neigh_table_init(struct neigh_table *tbl)
		{
		struct neigh_table *tmp;

		neigh_table_init_no_netlink(tbl);
		write_lock(&neigh_tbl_lock);
		for (tmp = neigh_tables; tmp; tmp = tmp->next) {
		if (tmp->family == tbl->family)
		break;
		}
		tbl->next = neigh_tables;
		neigh_tables = tbl;
		write_unlock(&neigh_tbl_lock);

		if (unlikely(tmp)) {
		printk(KERN_ERR "NEIGH: Registering multiple tables for "
		"family %d\n", tbl->family);
		dump_stack();
		}
		}

		int neigh_table_clear(struct neigh_table *tbl)
		@@ -2657,6 +2673,7 @@ EXPORT_SYMBOL(neigh_rand_reach_time);
		EXPORT_SYMBOL(neigh_resolve_output);
		EXPORT_SYMBOL(neigh_table_clear);
		EXPORT_SYMBOL(neigh_table_init);
		EXPORT_SYMBOL(neigh_table_init_no_netlink);
		EXPORT_SYMBOL(neigh_update);
		EXPORT_SYMBOL(neigh_update_hhs);
		EXPORT_SYMBOL(pneigh_enqueue);

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