Re: [PATCH] ethtool: fix a missing-check bug

[David Miller]

From: Wenwen Wang <wang6495@xxxxxxx>
Date: Tue,  9 Oct 2018 08:15:38 -0500

> In ethtool_get_rxnfc(), the eth command 'cmd' is compared against
> 'ETHTOOL_GRXFH' to see whether it is necessary to adjust the variable
> 'info_size'. Then the whole structure of 'info' is copied from the
> user-space buffer 'useraddr' with 'info_size' bytes. In the following
> execution, 'info' may be copied again from the buffer 'useraddr' depending
> on the 'cmd' and the 'info.flow_type'. However, after these two copies,
> there is no check between 'cmd' and 'info.cmd'. In fact, 'cmd' is also
> copied from the buffer 'useraddr' in dev_ethtool(), which is the caller
> function of ethtool_get_rxnfc(). Given that 'useraddr' is in the user
> space, a malicious user can race to change the eth command in the buffer
> between these copies. By doing so, the attacker can supply inconsistent
> data and cause undefined behavior because in the following execution 'info'
> will be passed to ops->get_rxnfc().
> 
> This patch adds a necessary check on 'info.cmd' and 'cmd' to confirm that
> they are still same after the two copies in ethtool_get_rxnfc(). Otherwise,
> an error code EINVAL will be returned.
> 
> Signed-off-by: Wenwen Wang <wang6495@xxxxxxx>

Applied.