[kernel-hardening] Re: [PATCH 27/38] sctp: Copy struct sctp_sock.autoclose to userspace using put_user()

Laura Abbott
2018-01-18T21:31:42Z

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;
> }
>