On Thu, Jan 18, 2018 at 1:31 PM, Laura Abbott [off-list ref] wrote:

On 01/10/2018 06:02 PM, Kees Cook wrote:

quoted

From: David Windsor <redacted>

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

quoted

Signed-off-by: David Windsor <redacted>
[kees: adjust commit log]
Cc: Vlad Yasevich <redacted>
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 <redacted>
---
  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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