Re: [PATCH] net: cxgb3_main: fix a missing-check bug

[David Miller <davem@davemloft.net>]

From: Wenwen Wang <wang6495@umn.edu>
Date: Fri,  5 Oct 2018 08:48:27 -0500

> In cxgb_extension_ioctl(), the command of the ioctl is firstly copied from
> the user-space buffer 'useraddr' to 'cmd' and checked through the
> switch statement. If the command is not as expected, an error code
> EOPNOTSUPP is returned. In the following execution, i.e., the cases of the
> switch statement, the whole buffer of 'useraddr' is copied again to a
> specific data structure, according to what kind of command is requested.
> However, after the second copy, there is no re-check on the newly-copied
> command. Given that the buffer 'useraddr' is in the user space, a malicious
> user can race to change the command between the two copies. By doing so,
> the attacker can supply malicious data to the kernel and cause undefined
> behavior.
> 
> This patch adds a re-check in each case of the switch statement if there is
> a second copy in that case, to re-check whether the command obtained in the
> second copy is the same as the one in the first copy. If not, an error code
> EINVAL is returned.
> 
> Signed-off-by: Wenwen Wang <wang6495@umn.edu>

Applied.