From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Duyck Subject: Re: [PATCH] net: add checks if dev->netdev_ops is NULL in register_netdevice() Date: Mon, 08 Apr 2013 08:49:33 -0700 Message-ID: <5162E70D.6070400@intel.com> References: <51629159.9040000@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , Eric Dumazet , Netdev , Li Zefan , Xinwei Hu To: dingtianhong Return-path: Received: from mga03.intel.com ([143.182.124.21]:21841 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936409Ab3DHPtg (ORCPT ); Mon, 8 Apr 2013 11:49:36 -0400 In-Reply-To: <51629159.9040000@huawei.com> Sender: netdev-owner@vger.kernel.org List-ID: On 04/08/2013 02:43 AM, dingtianhong wrote: > In some cases netdev->netdev_ops could be NULL in the register_netdevice(), > thus a NULL point deference happens and lead to oops: > > [ 8260.836400] BUG: unable to handle kernel NULL pointer dereference at (null) > [ 8260.955306] IP: [] register_netdevice+0x73/0x2d0 > [ 8261.054888] PGD 2f4dcd067 PUD 2f4de0067 PMD 0 > [ 8261.134244] Oops: 0000 [#1] SMP > [ 8261.198938] CPU 0 > [ 8262.605182] RIP: 0010:[] [] register_netdevice+0x73/0x2d0 > [ 8262.741859] RSP: 0018:ffff8802f489f9f8 EFLAGS: 00010246 > [ 8262.839463] RAX: 0000000000000000 RBX: ffff8802f4e73000 RCX: ffff8802f4e73006 > [ 8262.959484] RDX: 0000000000000000 RSI: 00000000daa92527 RDI: ffff8802f4e73006 > [ 8263.079352] RBP: 0000000000000000 R08: 0000000000000000 R09: ffff880327d898c0 > [ 8263.198987] R10: 00000000000000c1 R11: 0000000000000000 R12: ffffffff81fed080 > [ 8263.318401] R13: ffffffff81fed080 R14: ffff8802f4e73000 R15: 0000000000000000 > [ 8263.438014] FS: 00007f01dfa81700(0000) GS:ffff88033f200000(0000) knlGS:0000000000000000 > [ 8263.569778] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 8263.673859] CR2: 0000000000000000 CR3: 000000032893f000 CR4: 00000000000006f0 > [ 8263.794922] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 8263.915734] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > [ 8264.036251] Process rmcli (pid: 14089, threadinfo ffff8802f489e000, task ffff880324708080) > [ 8264.170961] Stack: > [ 8264.231328] ffff88032a3c0000 0000000000000003 0000000000000003 ffff88032a3c0000 > [ 8264.356967] 0000000000000003 ffffffffa039dbcb 000000003ec216c0 0000000000000246 > [ 8264.483081] 382e30363238205b 00205d3900000006 ff00305f63696e76 0000000000000003 > > We should check the point to avoid the oops. > > Signed-off-by: Ding Tianhong > --- > net/core/dev.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/core/dev.c b/net/core/dev.c > index e7d68ed..596a11e 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -5159,7 +5159,7 @@ int register_netdevice(struct net_device *dev) > goto out; > > /* Init, if this function is available */ > - if (dev->netdev_ops->ndo_init) { > + if (dev->netdev_ops && dev->netdev_ops->ndo_init) { > ret = dev->netdev_ops->ndo_init(dev); > if (ret) { > if (ret > 0) > -- 1.8.0 > The correct fix for this is to not allow the registration of devices with a null netdev_ops pointer. The subtle approach to resolving this is adding a check for the null pointer near the start of the function and returning -EVINAL since the dev structure passed was configured incorrectly. The blunt approach is to just add a BUG_ON with a comment on the line before it explaining that you should always set the netdev_ops pointer before trying to register a netdev. That way if someone else makes the mistake then they will hit the BUG_ON and realize what they are doing wrong. Thanks, Alex