Patchwork netfilter: fix ordering of jumpstack allocation and table update

login
register
mail settings
Submitter Will Deacon
Date Oct. 21, 2013, 12:14 p.m.
Message ID <20131021121452.GA29250@mudshark.cambridge.arm.com>
Download mbox | patch
Permalink /patch/285185/
State Accepted
Headers show

Comments

Will Deacon - Oct. 21, 2013, 12:14 p.m.
On Fri, Oct 18, 2013 at 06:18:13PM +0100, Eric Dumazet wrote:
> On Fri, 2013-10-18 at 17:57 +0100, Will Deacon wrote:
> > Hi Pablo,
> > 
> 
> > > We also need fixes for net/ipv6/netfilter/ip6_tables.c and
> > > net/ipv4/netfilter/arp_tables.c as well. Could you extend this patch
> > > and resend?
> > 
> > Sure, I can try, but that's going to require a bit of time to sit down and
> > look at the shared data, access order, dependencies etc. I'm currently
> > preparing for Edinburgh, so it might be a while before I get a chance to
> > extend this.
> 
> That's basically same code copy/pasted, so it should be relatively easy.

Ok, I took a look and I think I see what you mean: there are just some
additional consumers of the tables, so there aren't any additional writers
afaict (at least, net/bridge/netfilter/ebtables.c uses rw locks so we don't
have an issue there).

Attempt at an updated patch below.

Cheers,

Will

--->8

From 128bff68debba70c3cec4b4ac01050d7e864aa83 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Thu, 17 Oct 2013 13:34:13 +0100
Subject: [PATCH v2] netfilter: fix ordering of jumpstack allocation and table
 update

During kernel stability testing on an SMP ARMv7 system, Yalin Wang
reported the following panic from the netfilter code:

  1fe0: 0000001c 5e2d3b10 4007e779 4009e110 60000010 00000032 ff565656 ff545454
  [<c06c48dc>] (ipt_do_table+0x448/0x584) from [<c0655ef0>] (nf_iterate+0x48/0x7c)
  [<c0655ef0>] (nf_iterate+0x48/0x7c) from [<c0655f7c>] (nf_hook_slow+0x58/0x104)
  [<c0655f7c>] (nf_hook_slow+0x58/0x104) from [<c0683bbc>] (ip_local_deliver+0x88/0xa8)
  [<c0683bbc>] (ip_local_deliver+0x88/0xa8) from [<c0683718>] (ip_rcv_finish+0x418/0x43c)
  [<c0683718>] (ip_rcv_finish+0x418/0x43c) from [<c062b1c4>] (__netif_receive_skb+0x4cc/0x598)
  [<c062b1c4>] (__netif_receive_skb+0x4cc/0x598) from [<c062b314>] (process_backlog+0x84/0x158)
  [<c062b314>] (process_backlog+0x84/0x158) from [<c062de84>] (net_rx_action+0x70/0x1dc)
  [<c062de84>] (net_rx_action+0x70/0x1dc) from [<c0088230>] (__do_softirq+0x11c/0x27c)
  [<c0088230>] (__do_softirq+0x11c/0x27c) from [<c008857c>] (do_softirq+0x44/0x50)
  [<c008857c>] (do_softirq+0x44/0x50) from [<c0088614>] (local_bh_enable_ip+0x8c/0xd0)
  [<c0088614>] (local_bh_enable_ip+0x8c/0xd0) from [<c06b0330>] (inet_stream_connect+0x164/0x298)
  [<c06b0330>] (inet_stream_connect+0x164/0x298) from [<c061d68c>] (sys_connect+0x88/0xc8)
  [<c061d68c>] (sys_connect+0x88/0xc8) from [<c000e340>] (ret_fast_syscall+0x0/0x30)
  Code: 2a000021 e59d2028 e59de01c e59f011c (e7824103)
  ---[ end trace da227214a82491bd ]---
  Kernel panic - not syncing: Fatal exception in interrupt

This comes about because CPU1 is executing xt_replace_table in response
to a setsockopt syscall, resulting in:

	ret = xt_jumpstack_alloc(newinfo);
		--> newinfo->jumpstack = kzalloc(size, GFP_KERNEL);

	[...]

	table->private = newinfo;
	newinfo->initial_entries = private->initial_entries;

Meanwhile, CPU0 is handling the network receive path and ends up in
ipt_do_table, resulting in:

	private = table->private;

	[...]

	jumpstack  = (struct ipt_entry **)private->jumpstack[cpu];

On weakly ordered memory architectures, the writes to table->private
and newinfo->jumpstack from CPU1 can be observed out of order by CPU0.
Furthermore, on architectures which don't respect ordering of address
dependencies (i.e. Alpha), the reads from CPU0 can also be re-ordered.

This patch adds an smp_wmb() before the assignment to table->private
(which is essentially publishing newinfo) to ensure that all writes to
newinfo will be observed before plugging it into the table structure.
A dependent-read barrier is also added on the consumer sides, to ensure
the same ordering requirements are also respected there.

Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Eric Dumazet <edumazet@google.com>
Reported-by: Wang, Yalin <Yalin.Wang@sonymobile.com>
Tested-by: Wang, Yalin <Yalin.Wang@sonymobile.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 net/ipv4/netfilter/arp_tables.c | 5 +++++
 net/ipv4/netfilter/ip_tables.c  | 5 +++++
 net/ipv6/netfilter/ip6_tables.c | 5 +++++
 net/netfilter/x_tables.c        | 7 ++++++-
 4 files changed, 21 insertions(+), 1 deletion(-)
Pablo Neira - Oct. 22, 2013, 8:21 a.m.
On Mon, Oct 21, 2013 at 01:14:53PM +0100, Will Deacon wrote:
> On Fri, Oct 18, 2013 at 06:18:13PM +0100, Eric Dumazet wrote:
> > On Fri, 2013-10-18 at 17:57 +0100, Will Deacon wrote:
> > > Hi Pablo,
> > > 
> > 
> > > > We also need fixes for net/ipv6/netfilter/ip6_tables.c and
> > > > net/ipv4/netfilter/arp_tables.c as well. Could you extend this patch
> > > > and resend?
> > > 
> > > Sure, I can try, but that's going to require a bit of time to sit down and
> > > look at the shared data, access order, dependencies etc. I'm currently
> > > preparing for Edinburgh, so it might be a while before I get a chance to
> > > extend this.
> > 
> > That's basically same code copy/pasted, so it should be relatively easy.
> 
> Ok, I took a look and I think I see what you mean: there are just some
> additional consumers of the tables, so there aren't any additional writers
> afaict (at least, net/bridge/netfilter/ebtables.c uses rw locks so we don't
> have an issue there).
> 
> Attempt at an updated patch below.

Applied, thanks Will.
--
To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 85a4f21..59da7cd 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -271,6 +271,11 @@  unsigned int arpt_do_table(struct sk_buff *skb,
 	local_bh_disable();
 	addend = xt_write_recseq_begin();
 	private = table->private;
+	/*
+	 * Ensure we load private-> members after we've fetched the base
+	 * pointer.
+	 */
+	smp_read_barrier_depends();
 	table_base = private->entries[smp_processor_id()];
 
 	e = get_entry(table_base, private->hook_entry[hook]);
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index d23118d..718dfbd 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -327,6 +327,11 @@  ipt_do_table(struct sk_buff *skb,
 	addend = xt_write_recseq_begin();
 	private = table->private;
 	cpu        = smp_processor_id();
+	/*
+	 * Ensure we load private-> members after we've fetched the base
+	 * pointer.
+	 */
+	smp_read_barrier_depends();
 	table_base = private->entries[cpu];
 	jumpstack  = (struct ipt_entry **)private->jumpstack[cpu];
 	stackptr   = per_cpu_ptr(private->stackptr, cpu);
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 44400c2..710238f 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -349,6 +349,11 @@  ip6t_do_table(struct sk_buff *skb,
 	local_bh_disable();
 	addend = xt_write_recseq_begin();
 	private = table->private;
+	/*
+	 * Ensure we load private-> members after we've fetched the base
+	 * pointer.
+	 */
+	smp_read_barrier_depends();
 	cpu        = smp_processor_id();
 	table_base = private->entries[cpu];
 	jumpstack  = (struct ip6t_entry **)private->jumpstack[cpu];
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 8b03028..227aa11 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -845,8 +845,13 @@  xt_replace_table(struct xt_table *table,
 		return NULL;
 	}
 
-	table->private = newinfo;
 	newinfo->initial_entries = private->initial_entries;
+	/*
+	 * Ensure contents of newinfo are visible before assigning to
+	 * private.
+	 */
+	smp_wmb();
+	table->private = newinfo;
 
 	/*
 	 * Even though table entries have now been swapped, other CPU's