From: Wenwen Wang <wang6495@umn.edu>
Date: Tue, 9 Oct 2018 08:15:38 -0500
Subject: ethtool: fix a missing-check bug
Patch-mainline: v4.19
Git-commit: 2bb3207dbbd4d30e96dd0e1c8e013104193bd59c
References: bsc#1109837

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@umn.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/core/ethtool.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -1036,6 +1036,9 @@ static noinline_for_stack int ethtool_ge
 			return -EFAULT;
 	}
 
+	if (info.cmd != cmd)
+		return -EINVAL;
+
 	if (info.cmd == ETHTOOL_GRXCLSRLALL) {
 		if (info.rule_cnt > 0) {
 			if (info.rule_cnt <= KMALLOC_MAX_SIZE / sizeof(u32))