[PATCH 3.16 260/366] net: atm: Fix potential Spectre v1

Ben Hutchings
2018-10-14T23:12:04Z

From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>

commit acf784bd0ce257fe43da7ca266f7a10b837479d2 upstream.

ioc_data.dev_num can be controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:
net/atm/lec.c:702 lec_vcc_attach() warn: potential spectre issue
'dev_lec'

Fix this by sanitizing ioc_data.dev_num before using it to index
dev_lec. Also, notice that there is another instance in which array
dev_lec is being indexed using ioc_data.dev_num at line 705:
lec_vcc_added(netdev_priv(dev_lec[ioc_data.dev_num]),

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/atm/lec.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

--- a/net/atm/lec.c
+++ b/net/atm/lec.c
@@ -41,6 +41,9 @@ static unsigned char bridge_ula_lec[] =
#include <linux/module.h>
#include <linux/init.h>

+/* Hardening for Spectre-v1 */
+#include <linux/nospec.h>
+
#include "lec.h"
#include "lec_arpc.h"
#include "resources.h"
@@ -695,8 +698,10 @@ static int lec_vcc_attach(struct atm_vcc
bytes_left = copy_from_user(&ioc_data, arg, sizeof(struct atmlec_ioc));
if (bytes_left != 0)
pr_info("copy from user failed for %d bytes\n", bytes_left);
- if (ioc_data.dev_num < 0 || ioc_data.dev_num >= MAX_LEC_ITF ||
- !dev_lec[ioc_data.dev_num])
+ if (ioc_data.dev_num < 0 || ioc_data.dev_num >= MAX_LEC_ITF)
+ return -EINVAL;
+ ioc_data.dev_num = array_index_nospec(ioc_data.dev_num, MAX_LEC_ITF);
+ if (!dev_lec[ioc_data.dev_num])
return -EINVAL;
vpriv = kmalloc(sizeof(struct lec_vcc_priv), GFP_KERNEL);
if (!vpriv)