linux-kernel - [PATCH v2 22/30] sctp: Copy struct sctp_sock.autoclose to userspace using put

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Message-Id: <1503956111-36652-23-git-send-email-keescook@chromium.org>
Date:   Mon, 28 Aug 2017 14:35:03 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.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, netdev@...r.kernel.org,
        linux-mm@...ck.org, kernel-hardening@...ts.openwall.com
Subject: [PATCH v2 22/30] sctp: Copy struct sctp_sock.autoclose to userspace using put_user()

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.

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 c8784cb216e4..a29e41e19d64 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -4882,7 +4882,7 @@ 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;
 }
-- 
2.7.4