[PATCH 4.14 003/101] ipv4: Fix potential Spectre v1 vulnerability

From: Greg Kroah-Hartman
Date: Mon Jan 07 2019 - 08:16:54 EST

4.14-stable review patch. If anyone has any objections, please let me know.


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

[ Upstream commit 5648451e30a0d13d11796574919a359025d52cce ]

vr.vifi is indirectly 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/ipv4/ipmr.c:1616 ipmr_ioctl() warn: potential spectre issue 'mrt->vif_table' [r] (local cap)
net/ipv4/ipmr.c:1690 ipmr_compat_ioctl() warn: potential spectre issue 'mrt->vif_table' [r] (local cap)

Fix this by sanitizing vr.vifi before using it to index mrt->vif_table'

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@xxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/ipv4/ipmr.c | 3 +++
1 file changed, 3 insertions(+)

--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -68,6 +68,8 @@
#include <linux/netconf.h>
#include <net/nexthop.h>

+#include <linux/nospec.h>
struct ipmr_rule {
struct fib_rule common;
@@ -1620,6 +1622,7 @@ int ipmr_compat_ioctl(struct sock *sk, u
return -EFAULT;
if (vr.vifi >= mrt->maxvif)
return -EINVAL;
+ vr.vifi = array_index_nospec(vr.vifi, mrt->maxvif);
vif = &mrt->vif_table[vr.vifi];
if (VIF_EXISTS(mrt, vr.vifi)) {