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Date:   Mon, 17 Jun 2019 14:56:05 +0800
From:   JingYi Hou <houjingyi647@gmail.com>
To:     davem@davemloft.net
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] net: remove duplicate fetch in sock_getsockopt
Message-ID: <20190617065605.GA5924@hjy-HP-Notebook>
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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>
---
 net/core/sock.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index 2b3701958486..932bcbf2d565 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1477,9 +1477,6 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
 	{
 		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));
-- 
2.20.1