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

[David Miller]

From: JingYi Hou <houjingyi647@xxxxxxxxx>
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 <houjingyi647@xxxxxxxxx>

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.