Re: [PATCH net] gtp: fix an use-before-init in gtp_newlink()

Hi,

Thanks for the review. Will send a new patch with the fixes soon.

---- Fujiwara

On Mon, Oct 26, 2020 at 6:05 AM Jakub Kicinski kuba@kernel.org wrote:

On Sat, 24 Oct 2020 15:42:33 +0000 Masahiro Fujiwara wrote:

...

*_pdp_find() from gtp_encap_recv() would trigger a crash when a peer sends GTP packets while creating new GTP device.

RIP: 0010:gtp1_pdp_find.isra.0+0x68/0x90 [gtp]

<SNIP> Call Trace: <IRQ> gtp_encap_recv+0xc2/0x2e0 [gtp] ? gtp1_pdp_find.isra.0+0x90/0x90 [gtp] udp_queue_rcv_one_skb+0x1fe/0x530 udp_queue_rcv_skb+0x40/0x1b0 udp_unicast_rcv_skb.isra.0+0x78/0x90 __udp4_lib_rcv+0x5af/0xc70 udp_rcv+0x1a/0x20 ip_protocol_deliver_rcu+0xc5/0x1b0 ip_local_deliver_finish+0x48/0x50 ip_local_deliver+0xe5/0xf0 ? ip_protocol_deliver_rcu+0x1b0/0x1b0

gtp_encap_enable() should be called after gtp_hastable_new() otherwise *_pdp_find() will access the uninitialized hash table.

Looks good, minor nits:

• is the time zone broken on your system? Looks like your email has arrived with the date far in the past, so the build systems have missed it. Could you double check the time on your system?

...

Fixes: 1e3a3abd8 ("gtp: make GTP sockets in gtp_newlink optional")

The hash looks short, should be at lest 12 chars:

Fixes: 1e3a3abd8b28 ("gtp: make GTP sockets in gtp_newlink optional")

...

Signed-off-by: Masahiro Fujiwara fujiwara.masahiro@gmail.com

...

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c index 8e47d0112e5d..6c56337b02a3 100644 --- a/drivers/net/gtp.c +++ b/drivers/net/gtp.c @@ -663,10 +663,6 @@ static int gtp_newlink(struct net *src_net, struct net_device *dev,

  gtp = netdev_priv(dev);

• err = gtp_encap_enable(gtp, data);
  

• if (err < 0)
  

•         return err;
  

• if (!data[IFLA_GTP_PDP_HASHSIZE]) {
          hashsize = 1024;
  } else {
  

@@ -676,13 +672,18 @@ static int gtp_newlink(struct net *src_net, struct net_device *dev, }

  err = gtp_hashtable_new(gtp, hashsize);

• if (err < 0) {
  

•         return err;
  

• }
  

no need for braces around single statement

...

• err = gtp_encap_enable(gtp, data);
  if (err < 0)
          goto out_encap;
  
  err = register_netdevice(dev);
  if (err < 0) {
          netdev_dbg(dev, "failed to register new netdev %d\n", err);
  

•         goto out_hashtable;
  

•         goto out_encap;
  }
  
  gn = net_generic(dev_net(dev), gtp_net_id);
  

@@ -693,11 +694,10 @@ static int gtp_newlink(struct net *src_net, struct net_device *dev,

  return 0;

-out_hashtable:

• kfree(gtp->addr_hash);
  

• kfree(gtp->tid_hash);
  

out_encap: gtp_encap_disable(gtp);

I'd personally move the out_hashtable: label here and keep it, just for clarity. Otherwise reader has to double check that gtp_encap_disable() can be safely called before gtp_encap_enable().

Also gtp_encap_disable() could change in the future breaking this assumption.

...

• kfree(gtp->addr_hash);
  

• kfree(gtp->tid_hash);
  return err;
  

}