[PATCH] ethtool: fix a missing-check bug

[Wenwen Wang]

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>
---
 net/core/ethtool.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index c9993c6..0136625 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -1015,6 +1015,9 @@ static noinline_for_stack int ethtool_get_rxnfc(struct net_device *dev,
 			return -EINVAL;
 	}
 
+	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))
-- 
2.7.4