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Date: Thu, 18 Jan 2018 13:36:03 -0800
From: Kees Cook <keescook@...omium.org>
To: Laura Abbott <labbott@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>, David Windsor <dave@...lcore.net>, 
	Vlad Yasevich <vyasevich@...il.com>, Neil Horman <nhorman@...driver.com>, 
	"David S. Miller" <davem@...emloft.net>, linux-sctp@...r.kernel.org, 
	Network Development <netdev@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Alexander Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, 
	Andy Lutomirski <luto@...nel.org>, Christoph Hellwig <hch@...radead.org>, Christoph Lameter <cl@...ux.com>, 
	Mark Rutland <mark.rutland@....com>, "Martin K. Petersen" <martin.petersen@...cle.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Christian Borntraeger <borntraeger@...ibm.com>, 
	Christoffer Dall <christoffer.dall@...aro.org>, Dave Kleikamp <dave.kleikamp@...cle.com>, 
	Jan Kara <jack@...e.cz>, Luis de Bethencourt <luisbg@...nel.org>, Marc Zyngier <marc.zyngier@....com>, 
	Rik van Riel <riel@...hat.com>, Matthew Garrett <mjg59@...gle.com>, 
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, 
	Linux-MM <linux-mm@...ck.org>, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 27/38] sctp: Copy struct sctp_sock.autoclose to userspace
 using put_user()

On Thu, Jan 18, 2018 at 1:31 PM, Laura Abbott <labbott@...hat.com> wrote:
> On 01/10/2018 06:02 PM, Kees Cook wrote:
>>
>> From: David Windsor <dave@...lcore.net>
>>
>> The autoclose field can be copied with put_user(), so there is no need to
>> use copy_to_user(). In both cases, hardened usercopy is being bypassed
>> since the size is constant, and not open to runtime manipulation.
>>
>> This patch is verbatim from Brad Spengler/PaX Team's PAX_USERCOPY
>> whitelisting code in the last public patch of grsecurity/PaX based on my
>> understanding of the code. Changes or omissions from the original code are
>> mine and don't reflect the original grsecurity/PaX code.
>>
>
> Just tried a quick rebase and it looks like this conflicts with
> c76f97c99ae6 ("sctp: make use of pre-calculated len")
> I don't think we can use put_user if we're copying via the full
> len?

It should be fine, since:

        len = sizeof(int);

c76f97c99ae6 just does a swap of sizeof(int) with len, put_user() will
work in either case, since autoclose will always be int sized.

-Kees

>
> Thanks,
> Laura
>
>
>> Signed-off-by: David Windsor <dave@...lcore.net>
>> [kees: adjust commit log]
>> Cc: Vlad Yasevich <vyasevich@...il.com>
>> Cc: Neil Horman <nhorman@...driver.com>
>> Cc: "David S. Miller" <davem@...emloft.net>
>> Cc: linux-sctp@...r.kernel.org
>> Cc: netdev@...r.kernel.org
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>   net/sctp/socket.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
>> index efbc8f52c531..15491491ec88 100644
>> --- a/net/sctp/socket.c
>> +++ b/net/sctp/socket.c
>> @@ -5011,7 +5011,7 @@ static int sctp_getsockopt_autoclose(struct sock
>> *sk, int len, char __user *optv
>>         len = sizeof(int);
>>         if (put_user(len, optlen))
>>                 return -EFAULT;
>> -       if (copy_to_user(optval, &sctp_sk(sk)->autoclose, sizeof(int)))
>> +       if (put_user(sctp_sk(sk)->autoclose, (int __user *)optval))
>>                 return -EFAULT;
>>         return 0;
>>   }
>>
>



-- 
Kees Cook
Pixel Security

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