netdev - Re: [PATCH] net: add checks if dev->netdev_ops is NULL in register

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Message-ID: <20130410134516.44945a5b@nehalam.linuxnetplumber.net>
Date:	Wed, 10 Apr 2013 13:45:16 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	dingtianhong <dingtianhong@...wei.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	Netdev <netdev@...r.kernel.org>, Li Zefan <lizefan@...wei.com>,
	Xinwei Hu <huxinwei@...wei.com>
Subject: Re: [PATCH] net: add checks if dev->netdev_ops is NULL in
 register_netdevice()

On Mon, 8 Apr 2013 17:43:53 +0800
dingtianhong <dingtianhong@...wei.com> 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: [<ffffffff81388333>] 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:[<ffffffff81388333>]  [<ffffffff81388333>] 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 <dingtianhong@...wei.com>

I notice you truncated the back trace. You should include the whole thing
so the buggy driver can be found and shot. If it is your own code fix it.

Adding a BUG_ON() is a waste, the NULL trap is the same effect.

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