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Subject: Re: [PATCH 27/38] sctp: Copy struct sctp_sock.autoclose to userspace
 using put_user()
To:     Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org
Cc:     David Windsor <dave@nullcore.net>,
        Vlad Yasevich <vyasevich@gmail.com>,
        Neil Horman <nhorman@tuxdriver.com>,
        "David S. Miller" <davem@davemloft.net>,
        linux-sctp@vger.kernel.org, netdev@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Christoph Lameter <cl@linux.com>,
        Mark Rutland <mark.rutland@arm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Christoffer Dall <christoffer.dall@linaro.org>,
        Dave Kleikamp <dave.kleikamp@oracle.com>,
        Jan Kara <jack@suse.cz>,
        Luis de Bethencourt <luisbg@kernel.org>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Rik van Riel <riel@redhat.com>,
        Matthew Garrett <mjg59@google.com>,
        linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-mm@kvack.org, kernel-hardening@lists.openwall.com
References: <1515636190-24061-1-git-send-email-keescook@chromium.org>
 <1515636190-24061-28-git-send-email-keescook@chromium.org>
From:   Laura Abbott <labbott@redhat.com>
Message-ID: <19a7add8-adaf-4ad4-6ae3-4a62967656b9@redhat.com>
Date:   Thu, 18 Jan 2018 13:31:42 -0800
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On 01/10/2018 06:02 PM, Kees Cook wrote:
> From: David Windsor <dave@nullcore.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?

Thanks,
Laura

> Signed-off-by: David Windsor <dave@nullcore.net>
> [kees: adjust commit log]
> Cc: Vlad Yasevich <vyasevich@gmail.com>
> Cc: Neil Horman <nhorman@tuxdriver.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: linux-sctp@vger.kernel.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.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;
>   }
>