[PATCH] net: socket: fix a missing-check bug

From: Wenwen Wang
Date: Thu Oct 18 2018 - 10:37:16 EST

In ethtool_ioctl(), the ioctl command 'ethcmd' is checked through a switch
statement to see whether it is necessary to pre-process the ethtool
structure, because, as mentioned in the comment, the structure
ethtool_rxnfc is defined with padding. If yes, a user-space buffer 'rxnfc'
is allocated through compat_alloc_user_space(). One thing to note here is
that, if 'ethcmd' is ETHTOOL_GRXCLSRLALL, the size of the buffer 'rxnfc' is
partially determined by 'rule_cnt', which is actually acquired from the
user-space buffer 'compat_rxnfc', i.e., 'compat_rxnfc->rule_cnt', through
get_user(). After 'rxnfc' is allocated, the data in the original user-space
buffer 'compat_rxnfc' is then copied to 'rxnfc' through copy_in_user(),
including the 'rule_cnt' field. However, after this copy, no check is
re-enforced on 'rxnfc->rule_cnt'. So it is possible that a malicious user
race to change the value in the 'compat_rxnfc->rule_cnt' between these two
copies. Through this way, the attacker can bypass the previous check on
'rule_cnt' and inject malicious data. This can cause undefined behavior of
the kernel and introduce potential security risk.

This patch avoids the above issue via copying the value acquired by
get_user() to 'rxnfc->rule_cn', if 'ethcmd' is ETHTOOL_GRXCLSRLALL.

Signed-off-by: Wenwen Wang <wang6495@xxxxxxx>
net/socket.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/net/socket.c b/net/socket.c
index 01f3f8f..390a8ec 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2875,9 +2875,14 @@ static int ethtool_ioctl(struct net *net, struct compat_ifreq __user *ifr32)
(void __user *)(&rxnfc->fs.location + 1) -
- (void __user *)&rxnfc->fs.ring_cookie) ||
- copy_in_user(&rxnfc->rule_cnt, &compat_rxnfc->rule_cnt,
- sizeof(rxnfc->rule_cnt)))
+ (void __user *)&rxnfc->fs.ring_cookie))
+ return -EFAULT;
+ if (ethcmd == ETHTOOL_GRXCLSRLALL) {
+ if (put_user(rule_cnt, &rxnfc->rule_cnt))
+ return -EFAULT;
+ } else if (copy_in_user(&rxnfc->rule_cnt,
+ &compat_rxnfc->rule_cnt,
+ sizeof(rxnfc->rule_cnt)))
return -EFAULT;