ipv4: Fix potential Spectre v1 vulnerability

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@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
CVE-2017-5753

(cherry picked from commit 5648451e30a0d13d11796574919a359025d52cce)
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index e86322a0699f4a57aff78cf017457b97cdd5581e..a5a61cb6df4ebecca1898807c9649ccd39e9b326 100644 (file)
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -69,6 +69,8 @@
 #include <net/nexthop.h>
 #include <net/switchdev.h>
 
+#include <linux/nospec.h>
+
 struct ipmr_rule {
        struct fib_rule         common;
 };
@@ -1681,6 +1683,7 @@ int ipmr_ioctl(struct sock *sk, int cmd, void __user *arg)
                        return -EFAULT;
                if (vr.vifi >= mrt->maxvif)
                        return -EINVAL;
+               vr.vifi = array_index_nospec(vr.vifi, mrt->maxvif);
                read_lock(&mrt_lock);
                vif = &mrt->vif_table[vr.vifi];
                if (VIF_EXISTS(mrt, vr.vifi)) {
@@ -1755,6 +1758,7 @@ int ipmr_compat_ioctl(struct sock *sk, unsigned int cmd, void __user *arg)
                        return -EFAULT;
                if (vr.vifi >= mrt->maxvif)
                        return -EINVAL;
+               vr.vifi = array_index_nospec(vr.vifi, mrt->maxvif);
                read_lock(&mrt_lock);
                vif = &mrt->vif_table[vr.vifi];
                if (VIF_EXISTS(mrt, vr.vifi)) {