[PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[Thomas Graf]

/proc/net/ipv6_route reflects the contents of fib_table_hash. The proc
handler is installed in ip6_route_net_init() whereas fib_table_hash is
allocated in fib6_net_init() _after_ the proc handler has been installed.

This opens up a short time frame to access fib_table_hash with its pants
down.

fib6_init() as a whole can't be moved to an earlier position as it also
registers the rtnetlink message handlers which should be registered at
the end. Therefore split it into fib6_init() which is run early and
fib6_init_late() to register the rtnetlink message handlers.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
---
 include/net/ip6_fib.h |    2 ++
 net/ipv6/ip6_fib.c    |   18 +++++++++++-------
 net/ipv6/route.c      |   16 +++++++++++-----
 3 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 0ae759a..209af13 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -271,6 +271,8 @@ extern void			fib6_run_gc(unsigned long expires,
 extern void			fib6_gc_cleanup(void);
 
 extern int			fib6_init(void);
+extern int			fib6_init_late(void);
+extern void			fib6_cleanup_late(void);
 
 #ifdef CONFIG_IPV6_MULTIPLE_TABLES
 extern int			fib6_rules_init(void);
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 74c21b9..fbd4aff 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -1692,21 +1692,25 @@ int __init fib6_init(void)
 	ret = register_pernet_subsys(&fib6_net_ops);
 	if (ret)
 		goto out_kmem_cache_create;
-
-	ret = __rtnl_register(PF_INET6, RTM_GETROUTE, NULL, inet6_dump_fib,
-			      NULL);
-	if (ret)
-		goto out_unregister_subsys;
 out:
 	return ret;
 
-out_unregister_subsys:
-	unregister_pernet_subsys(&fib6_net_ops);
 out_kmem_cache_create:
 	kmem_cache_destroy(fib6_node_kmem);
 	goto out;
 }
 
+int __init fib6_init_late(void)
+{
+	return __rtnl_register(PF_INET6, RTM_GETROUTE, NULL, inet6_dump_fib,
+			       NULL);
+}
+
+void fib6_cleanup_late(void)
+{
+	rtnl_unregister(PF_INET6, RTM_GETROUTE);
+}
+
 void fib6_gc_cleanup(void)
 {
 	unregister_pernet_subsys(&fib6_net_ops);
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 999a982..dc60bf5 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3018,10 +3018,14 @@ int __init ip6_route_init(void)
 	if (ret)
 		goto out_kmem_cache;
 
-	ret = register_pernet_subsys(&ip6_route_net_ops);
+	ret = fib6_init();
 	if (ret)
 		goto out_dst_entries;
 
+	ret = register_pernet_subsys(&ip6_route_net_ops);
+	if (ret)
+		goto out_fib6_init;
+
 	ip6_dst_blackhole_ops.kmem_cachep = ip6_dst_ops_template.kmem_cachep;
 
 	/* Registering of the loopback is done before this portion of code,
@@ -3035,13 +3039,13 @@ int __init ip6_route_init(void)
 	init_net.ipv6.ip6_blk_hole_entry->dst.dev = init_net.loopback_dev;
 	init_net.ipv6.ip6_blk_hole_entry->rt6i_idev = in6_dev_get(init_net.loopback_dev);
   #endif
-	ret = fib6_init();
+	ret = fib6_init_late();
 	if (ret)
 		goto out_register_subsys;
 
 	ret = xfrm6_init();
 	if (ret)
-		goto out_fib6_init;
+		goto out_fib6_init_late;
 
 	ret = fib6_rules_init();
 	if (ret)
@@ -3064,10 +3068,12 @@ fib6_rules_init:
 	fib6_rules_cleanup();
 xfrm6_init:
 	xfrm6_fini();
-out_fib6_init:
-	fib6_gc_cleanup();
+out_fib6_init_late:
+	fib6_cleanup_late();
 out_register_subsys:
 	unregister_pernet_subsys(&ip6_route_net_ops);
+out_fib6_init:
+	fib6_gc_cleanup();
 out_dst_entries:
 	dst_entries_destroy(&ip6_dst_blackhole_ops);
 out_kmem_cache:
-- 
1.7.7.6

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[Neil Horman]

On Fri, Jun 15, 2012 at 11:00:17AM +0200, Thomas Graf wrote:
> /proc/net/ipv6_route reflects the contents of fib_table_hash. The proc
> handler is installed in ip6_route_net_init() whereas fib_table_hash is
> allocated in fib6_net_init() _after_ the proc handler has been installed.
> 
> This opens up a short time frame to access fib_table_hash with its pants
> down.
> 
> fib6_init() as a whole can't be moved to an earlier position as it also
> registers the rtnetlink message handlers which should be registered at
> the end. Therefore split it into fib6_init() which is run early and
> fib6_init_late() to register the rtnetlink message handlers.
> 
> Signed-off-by: Thomas Graf <tgraf@suug.ch>
Reviewed-by: Neil Horman <nhorman@tuxdriver.com>

> 

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[David Miller]

From: Neil Horman <nhorman@tuxdriver.com>
Date: Fri, 15 Jun 2012 06:56:55 -0400

> On Fri, Jun 15, 2012 at 11:00:17AM +0200, Thomas Graf wrote:
>> /proc/net/ipv6_route reflects the contents of fib_table_hash. The proc
>> handler is installed in ip6_route_net_init() whereas fib_table_hash is
>> allocated in fib6_net_init() _after_ the proc handler has been installed.
>> 
>> This opens up a short time frame to access fib_table_hash with its pants
>> down.
>> 
>> fib6_init() as a whole can't be moved to an earlier position as it also
>> registers the rtnetlink message handlers which should be registered at
>> the end. Therefore split it into fib6_init() which is run early and
>> fib6_init_late() to register the rtnetlink message handlers.
>> 
>> Signed-off-by: Thomas Graf <tgraf@suug.ch>
> Reviewed-by: Neil Horman <nhorman@tuxdriver.com>

Applied.

Since you're snooping around in here, you might notice that on network
namespace shutdown, we leak all user configured ipv6 FIB rules.

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[David Miller]

From: David Miller <davem@davemloft.net>
Date: Fri, 15 Jun 2012 15:32:40 -0700 (PDT)

> From: Neil Horman <nhorman@tuxdriver.com>
> Date: Fri, 15 Jun 2012 06:56:55 -0400
> 
>> On Fri, Jun 15, 2012 at 11:00:17AM +0200, Thomas Graf wrote:
>>> /proc/net/ipv6_route reflects the contents of fib_table_hash. The proc
>>> handler is installed in ip6_route_net_init() whereas fib_table_hash is
>>> allocated in fib6_net_init() _after_ the proc handler has been installed.
>>> 
>>> This opens up a short time frame to access fib_table_hash with its pants
>>> down.
>>> 
>>> fib6_init() as a whole can't be moved to an earlier position as it also
>>> registers the rtnetlink message handlers which should be registered at
>>> the end. Therefore split it into fib6_init() which is run early and
>>> fib6_init_late() to register the rtnetlink message handlers.
>>> 
>>> Signed-off-by: Thomas Graf <tgraf@suug.ch>
>> Reviewed-by: Neil Horman <nhorman@tuxdriver.com>
> 
> Applied.
> 
> Since you're snooping around in here, you might notice that on network
> namespace shutdown, we leak all user configured ipv6 FIB rules.

Thomas, this patch is buggy.

We will now initialize fib6_init() before ip6_net_route_net_ops is registerd.

This causes fib6_net_init() to run before net->ipv6.ip6_null_entry it
initialized.

Any route lookup will crash when we dereference a root's ->leaf
because it will be NULL.

Please test your changes more thoroughly.

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[David Miller]

From: David Miller <davem@davemloft.net>
Date: Fri, 15 Jun 2012 22:15:02 -0700 (PDT)

> We will now initialize fib6_init() before ip6_net_route_net_ops is registerd.
> 
> This causes fib6_net_init() to run before net->ipv6.ip6_null_entry it
> initialized.
> 
> Any route lookup will crash when we dereference a root's ->leaf
> because it will be NULL.

I've decided to revert this change for now.

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[Neil Horman]

On Fri, Jun 15, 2012 at 10:15:02PM -0700, David Miller wrote:
> From: David Miller <davem@davemloft.net>
> Date: Fri, 15 Jun 2012 15:32:40 -0700 (PDT)
> 
> > From: Neil Horman <nhorman@tuxdriver.com>
> > Date: Fri, 15 Jun 2012 06:56:55 -0400
> > 
> >> On Fri, Jun 15, 2012 at 11:00:17AM +0200, Thomas Graf wrote:
> >>> /proc/net/ipv6_route reflects the contents of fib_table_hash. The proc
> >>> handler is installed in ip6_route_net_init() whereas fib_table_hash is
> >>> allocated in fib6_net_init() _after_ the proc handler has been installed.
> >>> 
> >>> This opens up a short time frame to access fib_table_hash with its pants
> >>> down.
> >>> 
> >>> fib6_init() as a whole can't be moved to an earlier position as it also
> >>> registers the rtnetlink message handlers which should be registered at
> >>> the end. Therefore split it into fib6_init() which is run early and
> >>> fib6_init_late() to register the rtnetlink message handlers.
> >>> 
> >>> Signed-off-by: Thomas Graf <tgraf@suug.ch>
> >> Reviewed-by: Neil Horman <nhorman@tuxdriver.com>
> > 
> > Applied.
> > 
> > Since you're snooping around in here, you might notice that on network
> > namespace shutdown, we leak all user configured ipv6 FIB rules.
> 
> Thomas, this patch is buggy.
> 
> We will now initialize fib6_init() before ip6_net_route_net_ops is registerd.
> 
> This causes fib6_net_init() to run before net->ipv6.ip6_null_entry it
> initialized.
> 
> Any route lookup will crash when we dereference a root's ->leaf
> because it will be NULL.
> 
Perhaps the flag on the proc file like we discussed might be the better way to
go after all here Thomas.

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[David Miller]

From: Neil Horman <nhorman@tuxdriver.com>
Date: Sat, 16 Jun 2012 09:07:23 -0400

> Perhaps the flag on the proc file like we discussed might be the
> better way to go after all here Thomas.

I suspect Thomas's general approach was fine, he just was trying
to hard. :-)

Just seperate exactly the procfs, sysctl, etc. stuff into a completely
seperate set of network namespace ops, and do it dead last in the
initialization list.

At least that is how I would approach the fix.

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[Thomas Graf]

On Fri, Jun 15, 2012 at 10:15:02PM -0700, David Miller wrote:
> Thomas, this patch is buggy.
> 
> We will now initialize fib6_init() before ip6_net_route_net_ops is registerd.
> 
> This causes fib6_net_init() to run before net->ipv6.ip6_null_entry it
> initialized.
> 
> Any route lookup will crash when we dereference a root's ->leaf
> because it will be NULL.
> 
> Please test your changes more thoroughly.

Sorry, that this has slipped through. I must have booted the wrong
kernel. I even had this run by an external tester to confirm that
the original panic disapppeared...

I'll come up with a new fix.

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[Thomas Graf]

On Fri, Jun 15, 2012 at 03:32:40PM -0700, David Miller wrote:
> Since you're snooping around in here, you might notice that on network
> namespace shutdown, we leak all user configured ipv6 FIB rules.

I looked into this. fib_rules_unregister() will free all rules
belonging to the address family in that namespace.

Or were you referring to other rules?

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[David Miller]

From: Thomas Graf <tgraf@suug.ch>
Date: Tue, 19 Jun 2012 07:36:02 -0400

> On Fri, Jun 15, 2012 at 03:32:40PM -0700, David Miller wrote:
>> Since you're snooping around in here, you might notice that on network
>> namespace shutdown, we leak all user configured ipv6 FIB rules.
> 
> I looked into this. fib_rules_unregister() will free all rules
> belonging to the address family in that namespace.
> 
> Or were you referring to other rules?

Sorry, the leak I saw was for the fib6 tables, not the rules
themselves.

IPV4 has ip_fib_net_exit() which walks the FIB4 table hash
and releases everything.

I couldn't find the IPV6 counterpart.  All I could find was code which
explicitly liberates the ipv6 main and local tables.

There is no ipv6 code I can find which traverses fib_table_hash and
liberates the dynamically generated tables.

Re: [PATCH] ipv6: Prevent access to uninitialized fib_table_hash via /proc/net/ipv6_route

[Sedat Dilek]

Hi,

I pulled net.git#master on top of latest Linus upstream GIT.

The revert [1] fixes machine's kernel-panic.
Thanks.

Regards,
- Sedat -


[1] http://git.kernel.org/?p=linux/kernel/git/davem/net.git;a=commitdiff;h=e8803b6c387129059e04d9e14d49efda250a7361