Subject: Re: [PATCH] sctp: use GFP_USER for user-controlled kmalloc

From: Daniel Borkmann <[email-masked]>
Date: Tue, 01 Dec 2015 12:29:40 +0100

On 12/01/2015 11:46 AM, David Laight wrote:
> From: Marcelo Ricardo Leitner
>> Sent: 30 November 2015 16:33
>> Dmitry Vyukov reported that the user could trigger a kernel warning by
>> using a large len value for getsockopt SCTP_GET_LOCAL_ADDRS, as that
>> value directly affects the value used as a kmalloc() parameter.
>>
>> This patch thus switches the allocation flags from all user-controllable
>> kmalloc size to GFP_USER to put some more restrictions on it and also
>> disables the warn, as they are not necessary.
>
> ISTM that the code should put some 'sanity limit' on that
> size before allocating the kernel buffer.

One could do that in addition, but this buffer has just a short lifetime
and by using GFP_USER hardwall restrictions apply already.