[PATCH] net: remove duplicate fetch in sock_getsockopt

[PATCH] net: remove duplicate fetch in sock_getsockopt

[JingYi Hou]

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

Re: [PATCH] net: remove duplicate fetch in sock_getsockopt

[David Miller]

From: JingYi Hou <houjingyi647@gmail.com>
Date: Mon, 17 Jun 2019 14:56:05 +0800

> 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>

Applied and queued up for -stable, thanks.