[PATCH] net: check for NULL net_device in FIB tables

struct fib_nh->nh_dev can be NULL, so we should check it before calling
__in_dev_get_rcu on it.

Multiple places seem to want this (and check the return value), so we can
add a convenience wrapper for this.

This fixes a crash in AF_NETLINK sendmsg().

Please double check that I caught all the callers that need the NULL
guard.

Fixes: 0eeb075fad73 ("net: ipv4 sysctl option to ignore routes when nexthop link is down")
Cc: Andy Gospodarek <redacted>
Cc: Dinesh Dutt <redacted>
Cc: Scott Feldman <redacted>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Vegard Nossum <redacted>
---
 include/linux/inetdevice.h | 7 +++++++
 net/ipv4/fib_semantics.c   | 8 ++++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/linux/inetdevice.h b/include/linux/inetdevice.h
index ee971f3..2d8bea1 100644
--- a/include/linux/inetdevice.h
+++ b/include/linux/inetdevice.h

@@ -222,6 +222,13 @@ static inline struct in_device *__in_dev_get_rtnl(const struct net_device *dev)
 	return rtnl_dereference(dev->ip_ptr);
 }
 
+static inline struct in_device *in_dev_get_rtnl(const struct net_device *dev)
+{
+	if (!dev)
+		return NULL;
+	return __in_dev_get_rtnl(dev);
+}
+
 static inline struct neigh_parms *__in_dev_arp_parms_get_rcu(const struct net_device *dev)
 {
 	struct in_device *in_dev = __in_dev_get_rcu(dev);

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index d09173b..8289799 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c

@@ -545,7 +545,7 @@ static void fib_rebalance(struct fib_info *fi)
 		if (nh->nh_flags & RTNH_F_DEAD)
 			continue;
 
-		in_dev = __in_dev_get_rtnl(nh->nh_dev);
+		in_dev = in_dev_get_rtnl(nh->nh_dev);
 
 		if (in_dev &&
 		    IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev) &&

@@ -559,7 +559,7 @@ static void fib_rebalance(struct fib_info *fi)
 	change_nexthops(fi) {
 		int upper_bound;
 
-		in_dev = __in_dev_get_rtnl(nexthop_nh->nh_dev);
+		in_dev = in_dev_get_rtnl(nexthop_nh->nh_dev);
 
 		if (nexthop_nh->nh_flags & RTNH_F_DEAD) {
 			upper_bound = -1;

@@ -1261,7 +1261,7 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
 		    nla_put_u32(skb, RTA_OIF, fi->fib_nh->nh_oif))
 			goto nla_put_failure;
 		if (fi->fib_nh->nh_flags & RTNH_F_LINKDOWN) {
-			in_dev = __in_dev_get_rtnl(fi->fib_nh->nh_dev);
+			in_dev = in_dev_get_rtnl(fi->fib_nh->nh_dev);
 			if (in_dev &&
 			    IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev))
 				rtm->rtm_flags |= RTNH_F_DEAD;

@@ -1292,7 +1292,7 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
 
 			rtnh->rtnh_flags = nh->nh_flags & 0xFF;
 			if (nh->nh_flags & RTNH_F_LINKDOWN) {
-				in_dev = __in_dev_get_rtnl(nh->nh_dev);
+				in_dev = in_dev_get_rtnl(nh->nh_dev);
 				if (in_dev &&
 				    IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev))
 					rtnh->rtnh_flags |= RTNH_F_DEAD;

-- 
1.9.1

On 07/04/2016 02:47 PM, Vegard Nossum wrote:

struct fib_nh->nh_dev can be NULL, so we should check it before calling
__in_dev_get_rcu on it.

That should say __in_dev_get_rtnl(), obviously.

Multiple places seem to want this (and check the return value), so we can
add a convenience wrapper for this.

This fixes a crash in AF_NETLINK sendmsg().

Please double check that I caught all the callers that need the NULL
guard.

Fixes: 0eeb075fad73 ("net: ipv4 sysctl option to ignore routes when nexthop link is down")
Cc: Andy Gospodarek <redacted>
Cc: Dinesh Dutt <redacted>
Cc: Scott Feldman <redacted>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Vegard Nossum <redacted>

I guess we could also add:

Cc: stable@vger.kernel.org


Vegard

	Hello,

On Mon, 4 Jul 2016, Vegard Nossum wrote:

struct fib_nh->nh_dev can be NULL, so we should check it before calling
__in_dev_get_rcu on it.

Multiple places seem to want this (and check the return value), so we can
add a convenience wrapper for this.

This fixes a crash in AF_NETLINK sendmsg().

Please double check that I caught all the callers that need the NULL
guard.

	What kind of configuration causes such crash?

	fib_rebalance can not crash because for multipath
routes (fib_nhs > 1) all nexthops should have valid nh_dev.

	Looks like this is the only place that can crash,
adding extra cycles to the other places is not good. And this
can happen only because fib_create_info() allows RTNH_F_LINKDOWN
to come for routes with error. May be fc_flags should be masked
there? Or there is another place that sets the flag when nh_dev
is NULL?

	Not needed because fib_nhs > 1

 				if (in_dev &&
 				    IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev))
 					rtnh->rtnh_flags |= RTNH_F_DEAD;
-- 

Regards

On 07/04/2016 09:45 PM, Julian Anastasov wrote:

	Hello,

On Mon, 4 Jul 2016, Vegard Nossum wrote:

quoted

struct fib_nh->nh_dev can be NULL, so we should check it before calling
__in_dev_get_rcu on it.

Multiple places seem to want this (and check the return value), so we can
add a convenience wrapper for this.

This fixes a crash in AF_NETLINK sendmsg().

Please double check that I caught all the callers that need the NULL
guard.

	What kind of configuration causes such crash?

It's not very easy to tell, sorry, I was using a netlink fuzzer to find
the crash. But see below, you identified the right bit of code.

quoted

-		in_dev = __in_dev_get_rtnl(nh->nh_dev);
+		in_dev = in_dev_get_rtnl(nh->nh_dev);

	fib_rebalance can not crash because for multipath
routes (fib_nhs > 1) all nexthops should have valid nh_dev.

Okay, cool.

quoted

  		if (in_dev &&
  		    IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev) &&

@@ -559,7 +559,7 @@ static void fib_rebalance(struct fib_info *fi)
  	change_nexthops(fi) {
  		int upper_bound;

-		in_dev = __in_dev_get_rtnl(nexthop_nh->nh_dev);
+		in_dev = in_dev_get_rtnl(nexthop_nh->nh_dev);

  		if (nexthop_nh->nh_flags & RTNH_F_DEAD) {
  			upper_bound = -1;

@@ -1261,7 +1261,7 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,
  		    nla_put_u32(skb, RTA_OIF, fi->fib_nh->nh_oif))
  			goto nla_put_failure;
  		if (fi->fib_nh->nh_flags & RTNH_F_LINKDOWN) {
-			in_dev = __in_dev_get_rtnl(fi->fib_nh->nh_dev);
+			in_dev = in_dev_get_rtnl(fi->fib_nh->nh_dev);

	Looks like this is the only place that can crash,
adding extra cycles to the other places is not good. And this
can happen only because fib_create_info() allows RTNH_F_LINKDOWN
to come for routes with error. May be fc_flags should be masked
there? Or there is another place that sets the flag when nh_dev
is NULL?

Indeed, this is the (only) place that actually crashed for me.

quoted

  			if (in_dev &&
  			    IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev))
  				rtm->rtm_flags |= RTNH_F_DEAD;

@@ -1292,7 +1292,7 @@ int fib_dump_info(struct sk_buff *skb, u32 portid, u32 seq, int event,

  			rtnh->rtnh_flags = nh->nh_flags & 0xFF;
  			if (nh->nh_flags & RTNH_F_LINKDOWN) {
-				in_dev = __in_dev_get_rtnl(nh->nh_dev);
+				in_dev = in_dev_get_rtnl(nh->nh_dev);

	Not needed because fib_nhs > 1

Alright.

Thanks for the review! I can submit a new patch to only check the one
place above that actually crashed. Otherwise, if you think it's better
to go with your fc_flags suggestion, feel free to send a patch for that.
As you can tell, I am not very familiar with this code :-) If you do
send a patch, I can test it easily.


Vegard

	Hello,

On Mon, 4 Jul 2016, Vegard Nossum wrote:

Alright.

Thanks for the review! I can submit a new patch to only check the one
place above that actually crashed. Otherwise, if you think it's better
to go with your fc_flags suggestion, feel free to send a patch for that.
As you can tell, I am not very familiar with this code :-) If you do
send a patch, I can test it easily.

	Of course, here is untested version. May be I'll do some
testing this weekend and will submit with proper commit
message...

[PATCH RFC] ipv4: reject RTNH_F_LINKDOWN for incompatible routes

The RTNH_F_LINKDOWN flag is used only for link routes.
Reject it for error routes and local routes.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
---
 net/ipv4/fib_semantics.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 2b68418..1f10c20 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c

@@ -1113,7 +1113,8 @@ struct fib_info *fib_create_info(struct fib_config *cfg)
 	}
 
 	if (fib_props[cfg->fc_type].error) {
-		if (cfg->fc_gw || cfg->fc_oif || cfg->fc_mp)
+		if (cfg->fc_gw || cfg->fc_oif || cfg->fc_mp ||
+		    (fi->fib_nh->nh_flags & RTNH_F_LINKDOWN))
 			goto err_inval;
 		goto link_it;
 	} else {

@@ -1136,7 +1137,7 @@ struct fib_info *fib_create_info(struct fib_config *cfg)
 		struct fib_nh *nh = fi->fib_nh;
 
 		/* Local address is added. */
-		if (nhs != 1 || nh->nh_gw)
+		if (nhs != 1 || nh->nh_gw || (nh->nh_flags & RTNH_F_LINKDOWN))
 			goto err_inval;
 		nh->nh_scope = RT_SCOPE_NOWHERE;
 		nh->nh_dev = dev_get_by_index(net, fi->fib_nh->nh_oif);

-- 
1.9.3

Regards

On 07/04/2016 11:24 PM, Julian Anastasov wrote:

	Hello,

On Mon, 4 Jul 2016, Vegard Nossum wrote:

quoted

Alright.

Thanks for the review! I can submit a new patch to only check the one
place above that actually crashed. Otherwise, if you think it's better
to go with your fc_flags suggestion, feel free to send a patch for that.
As you can tell, I am not very familiar with this code :-) If you do
send a patch, I can test it easily.

	Of course, here is untested version. May be I'll do some
testing this weekend and will submit with proper commit
message...

[PATCH RFC] ipv4: reject RTNH_F_LINKDOWN for incompatible routes

The RTNH_F_LINKDOWN flag is used only for link routes.
Reject it for error routes and local routes.

Signed-off-by: Julian Anastasov <ja@ssi.bg>

Tested your patch, it fixes the problem for me. I haven't tested if it
breaks anything else :-)


Vegard

	Hello,

On Tue, 5 Jul 2016, Vegard Nossum wrote:

quoted

[PATCH RFC] ipv4: reject RTNH_F_LINKDOWN for incompatible routes

The RTNH_F_LINKDOWN flag is used only for link routes.
Reject it for error routes and local routes.

Signed-off-by: Julian Anastasov <ja@ssi.bg>

Tested your patch, it fixes the problem for me. I haven't tested if it
breaks anything else :-)

	Thanks!

Regards