netdev - Re: [PATCH net] net: Fix undefined behavior in netdev name allocation

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Date: Tue, 14 Nov 2023 09:26:18 +0200
From: Gal Pressman <gal@...dia.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
 Vlad Buslov <vladbu@...dia.com>
Subject: Re: [PATCH net] net: Fix undefined behavior in netdev name allocation

On 14/11/2023 6:09, Jakub Kicinski wrote:
> On Mon, 13 Nov 2023 10:35:44 +0200 Gal Pressman wrote:
>> Cited commit removed the strscpy() call and kept the snprintf() only.
>>
>> When allocating a netdev, 'res' and 'name' pointers are equal, but
>> according to POSIX, if copying takes place between objects that overlap
>> as a result of a call to sprintf() or snprintf(), the results are
>> undefined.
>>
>> Add back the strscpy() and use 'buf' as an intermediate buffer.
> 
> It may be worth mentioning that it is fairly common to put the format
> in dev->name before device is registered, IOW this condition takes
> place a lot?

I'll mention it.

> IIUC once we cross into 3-digit IDs we may crash?

Right, the bitmap and names get out of sync, it results in sysfs name
collision call traces.

> 
> With that and the right fixes tag:
> 
> Reviewed-by: Jakub Kicinski <kuba@...nel.org>
> 
> Thanks!

Thanks Jakub!