[Patch net] ipv6: check for ip6_null_entry in __ip6_del_rt_siblings()

Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
-> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
because ip6_null_entry is returned in this path since ip6_null_entry
is kinda default for a ipv6 route table root node. Quote from
David Ahern:

 ip6_null_entry is the root of all ipv6 fib tables making it integrated
 into the table ...

We should ignore any attempt of trying to delete it, like we do in
__ip6_del_rt() path and several others.

Reported-by: Andrey Konovalov <redacted>
Signed-off-by: Cong Wang <redacted>
---
 net/ipv6/route.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f54f426..9da77e9 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
 static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 {
 	struct nl_info *info = &cfg->fc_nlinfo;
+	struct net *net = info->nl_net;
 	struct sk_buff *skb = NULL;
 	struct fib6_table *table;
 	int err;
 
+	if (rt == net->ipv6.ip6_null_entry)
+		return -ENOENT;
 	table = rt->rt6i_table;
 	write_lock_bh(&table->tb6_lock);
 

@@ -2184,7 +2187,7 @@ static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 		if (skb) {
 			u32 seq = info->nlh ? info->nlh->nlmsg_seq : 0;
 
-			if (rt6_fill_node(info->nl_net, skb, rt,
+			if (rt6_fill_node(net, skb, rt,
 					  NULL, NULL, 0, RTM_DELROUTE,
 					  info->portid, seq, 0) < 0) {
 				kfree_skb(skb);

@@ -2208,7 +2211,7 @@ static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 	ip6_rt_put(rt);
 
 	if (skb) {
-		rtnl_notify(skb, info->nl_net, info->portid, RTNLGRP_IPV6_ROUTE,
+		rtnl_notify(skb, net, info->portid, RTNLGRP_IPV6_ROUTE,
 			    info->nlh, gfp_any());
 	}
 	return err;

-- 
2.5.5

On Mon, 2017-02-27 at 11:07 -0800, Cong Wang wrote:

It looks the caller did a dst_hold(&rt->dst);

So this new error path would leave a refcount leak.

Note that I was not able to trigger the crash on old kernels, so it
would be nice to get a precise idea of bug origin.

Thanks.

On Mon, Feb 27, 2017 at 12:34 PM, Eric Dumazet [off-list ref] wrote:

On Mon, 2017-02-27 at 11:07 -0800, Cong Wang wrote:

quoted

Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
-> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
because ip6_null_entry is returned in this path since ip6_null_entry
is kinda default for a ipv6 route table root node. Quote from
David Ahern:

 ip6_null_entry is the root of all ipv6 fib tables making it integrated
 into the table ...

We should ignore any attempt of trying to delete it, like we do in
__ip6_del_rt() path and several others.

Reported-by: Andrey Konovalov <redacted>
Signed-off-by: Cong Wang <redacted>
---
 net/ipv6/route.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f54f426..9da77e9 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
 static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 {
      struct nl_info *info = &cfg->fc_nlinfo;
+     struct net *net = info->nl_net;
      struct sk_buff *skb = NULL;
      struct fib6_table *table;
      int err;

+     if (rt == net->ipv6.ip6_null_entry)
+             return -ENOENT;

It looks the caller did a dst_hold(&rt->dst);

So this new error path would leave a refcount leak.

Interesting, this error path is not new for __ip6_del_rt_siblings()
so the leak was already there before mine, but you are probably
right we have a leak here.

I will send a separate patch to address this leak.

Note that I was not able to trigger the crash on old kernels, so it
would be nice to get a precise idea of bug origin.

Right, I miss:
Fixes: 0ae8133586ad ("net: ipv6: Allow shorthand delete of all
nexthops in multipath route")

Thanks!

On 2/27/17 12:34 PM, Eric Dumazet wrote:

On Mon, 2017-02-27 at 11:07 -0800, Cong Wang wrote:

quoted

Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
-> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
because ip6_null_entry is returned in this path since ip6_null_entry
is kinda default for a ipv6 route table root node. Quote from
David Ahern:

 ip6_null_entry is the root of all ipv6 fib tables making it integrated
 into the table ...

We should ignore any attempt of trying to delete it, like we do in
__ip6_del_rt() path and several others.

Reported-by: Andrey Konovalov <redacted>
Signed-off-by: Cong Wang <redacted>
---
 net/ipv6/route.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f54f426..9da77e9 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
 static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 {
 	struct nl_info *info = &cfg->fc_nlinfo;
+	struct net *net = info->nl_net;
 	struct sk_buff *skb = NULL;
 	struct fib6_table *table;
 	int err;
 
+	if (rt == net->ipv6.ip6_null_entry)
+		return -ENOENT;

It looks the caller did a dst_hold(&rt->dst);

So this new error path would leave a refcount leak.

Note that I was not able to trigger the crash on old kernels, so it
would be nice to get a precise idea of bug origin.

Cong: do you want to send a v2 catching the null entry in ip6_route_del
before the refcnt?

                for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
+                       /* do not allow deletion of the null route */
+                       if (rt == net->ipv6.ip6_null_entry)
+                               continue;

Fixes: 0ae8133586ad net: ipv6: Allow shorthand delete of all nexthops in
multipath route

On Mon, Feb 27, 2017 at 1:00 PM, David Ahern [off-list ref] wrote:

On 2/27/17 12:34 PM, Eric Dumazet wrote:

quoted

On Mon, 2017-02-27 at 11:07 -0800, Cong Wang wrote:

quoted

Andrey reported a NULL pointer deref bug in ipv6_route_ioctl()
-> ip6_route_del() -> __ip6_del_rt_siblings() code path. This is
because ip6_null_entry is returned in this path since ip6_null_entry
is kinda default for a ipv6 route table root node. Quote from
David Ahern:

 ip6_null_entry is the root of all ipv6 fib tables making it integrated
 into the table ...

We should ignore any attempt of trying to delete it, like we do in
__ip6_del_rt() path and several others.

Reported-by: Andrey Konovalov <redacted>
Signed-off-by: Cong Wang <redacted>
---
 net/ipv6/route.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f54f426..9da77e9 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -2169,10 +2169,13 @@ int ip6_del_rt(struct rt6_info *rt)
 static int __ip6_del_rt_siblings(struct rt6_info *rt, struct fib6_config *cfg)
 {
     struct nl_info *info = &cfg->fc_nlinfo;
+    struct net *net = info->nl_net;
     struct sk_buff *skb = NULL;
     struct fib6_table *table;
     int err;

+    if (rt == net->ipv6.ip6_null_entry)
+            return -ENOENT;

It looks the caller did a dst_hold(&rt->dst);

So this new error path would leave a refcount leak.

Note that I was not able to trigger the crash on old kernels, so it
would be nice to get a precise idea of bug origin.

Cong: do you want to send a v2 catching the null entry in ip6_route_del
before the refcnt?

Yeah, actually it is introduced by my patch because there is already
an ip6_rt_put() in __ip6_del_rt_siblings(). So v2 is coming...

                for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
+                       /* do not allow deletion of the null route */
+                       if (rt == net->ipv6.ip6_null_entry)
+                               continue;

Fixes: 0ae8133586ad net: ipv6: Allow shorthand delete of all nexthops in
multipath route

Note, I moved the check into __ip6_del_rt_siblings() because __ip6_del_rt()
has a same check.

On 2/27/17 1:04 PM, Cong Wang wrote:

quoted

                for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
+                       /* do not allow deletion of the null route */
+                       if (rt == net->ipv6.ip6_null_entry)
+                               continue;

Fixes: 0ae8133586ad net: ipv6: Allow shorthand delete of all nexthops in
multipath route

Note, I moved the check into __ip6_del_rt_siblings() because __ip6_del_rt()
has a same check.

that's b/c __ip6_del_rt has a second call path. __ip6_del_rt_siblings is
new and is not expecting to see the null entry. Catching it before the
dst_hold would be better.

On Mon, Feb 27, 2017 at 1:06 PM, David Ahern [off-list ref] wrote:

On 2/27/17 1:04 PM, Cong Wang wrote:

quoted

quoted

                for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
+                       /* do not allow deletion of the null route */
+                       if (rt == net->ipv6.ip6_null_entry)
+                               continue;

Fixes: 0ae8133586ad net: ipv6: Allow shorthand delete of all nexthops in
multipath route

Note, I moved the check into __ip6_del_rt_siblings() because __ip6_del_rt()
has a same check.

that's b/c __ip6_del_rt has a second call path. __ip6_del_rt_siblings is
new and is not expecting to see the null entry. Catching it before the
dst_hold would be better.

Yeah, but it also depends on if we want to continue after the null entry,
at least __ip6_del_rt () returns an error for null entry, which looks more
correct than continuing to proceed after it.