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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, JingYi Hou <houjingyi647@gmail.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 4.19 54/72] net: remove duplicate fetch in sock_getsockopt
Date:   Tue,  2 Jul 2019 10:01:55 +0200
Message-Id: <20190702080127.383587532@linuxfoundation.org>
In-Reply-To: <20190702080124.564652899@linuxfoundation.org>
References: <20190702080124.564652899@linuxfoundation.org>
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From: JingYi Hou <houjingyi647@gmail.com>

[ Upstream commit d0bae4a0e3d8c5690a885204d7eb2341a5b4884d ]

In sock_getsockopt(), 'optlen' is fetched the first time from userspace.
'len < 0' is then checked. Then in condition 'SO_MEMINFO', 'optlen' is
fetched the second time from userspace.

If change it between two fetches may cause security problems or unexpected
behaivor, and there is no reason to fetch it a second time.

To fix this, we need to remove the second fetch.

Signed-off-by: JingYi Hou <houjingyi647@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/core/sock.c |    3 ---
 1 file changed, 3 deletions(-)

--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1348,9 +1348,6 @@ int sock_getsockopt(struct socket *sock,
 	{
 		u32 meminfo[SK_MEMINFO_VARS];
 
-		if (get_user(len, optlen))
-			return -EFAULT;
-
 		sk_get_meminfo(sk, meminfo);
 
 		len = min_t(unsigned int, len, sizeof(meminfo));