Re: [PATCH v2] ethtool: fix a potential missing-check bug

[David Miller]

From: Wenwen Wang <wang6495@xxxxxxx>
Date: Mon, 30 Apr 2018 12:31:13 -0500

> In ethtool_get_rxnfc(), the object "info" is firstly copied from
> user-space. If the FLOW_RSS flag is set in the member field flow_type of
> "info" (and cmd is ETHTOOL_GRXFH), info needs to be copied again from
> user-space because FLOW_RSS is newer and has new definition, as mentioned
> in the comment. However, given that the user data resides in user-space, a
> malicious user can race to change the data after the first copy. By doing
> so, the user can inject inconsistent data. For example, in the second
> copy, the FLOW_RSS flag could be cleared in the field flow_type of "info".
> In the following execution, "info" will be used in the function
> ops->get_rxnfc(). Such inconsistent data can potentially lead to unexpected
> information leakage since ops->get_rxnfc() will prepare various types of
> data according to flow_type, and the prepared data will be eventually
> copied to user-space. This inconsistent data may also cause undefined
> behaviors based on how ops->get_rxnfc() is implemented.
> 
> This patch simply re-verifies the flow_type field of "info" after the
> second copy. If the value is not as expected, an error code will be
> returned.
> 
> Signed-off-by: Wenwen Wang <wang6495@xxxxxxx>

Applied, thanks.