2019-06-13 15:34:35

by houjingyi

Subject: [PATCH] fix double-fetch bug in sock_getsockopt()

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 without check.

if a malicious user can change it between two fetches may cause security
problems or unexpected behaivor.

To fix this, we need to recheck it in the second fetch.

Signed-off-by: JingYi Hou <[email protected]>
---
net/core/sock.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/core/sock.c b/net/core/sock.c
index 2b3701958486..577780c935ee 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1479,6 +1479,8 @@ int sock_getsockopt(struct socket *sock, int level, int optname,

if (get_user(len, optlen))
return -EFAULT;
+ if (len < 0)
+ return -EINVAL;

sk_get_meminfo(sk, meminfo);

--
2.20.1

2019-06-15 20:33:27

by David Miller

Subject: Re: [PATCH] fix double-fetch bug in sock_getsockopt()

From: JingYi Hou <[email protected]>
Date: Thu, 13 Jun 2019 18:44:57 +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 without check.
>
> if a malicious user can change it between two fetches may cause security
> problems or unexpected behaivor.
>
> To fix this, we need to recheck it in the second fetch.
>
> Signed-off-by: JingYi Hou <[email protected]>

THere is no reason to fetch len a second time, so please just remove
the get_user() call here instead.

Also, please format your Subject line properly with appropriate subsystem
prefixes etc.