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ip6mr: Fix potential Spectre v1 vulnerability 

vr.mifi 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/ipv6/ip6mr.c:1845 ip6mr_ioctl() warn: potential spectre issue 'mrt->vif_table' [r] (local cap)
net/ipv6/ip6mr.c:1919 ip6mr_compat_ioctl() warn: potential spectre issue 'mrt->vif_table' [r] (local cap)

Fix this by sanitizing vr.mifi 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>
This commit is contained in:
Gustavo A. R. Silva 2018-12-11 14:10:08 -06:00 committed by David S. Miller
parent 51367e423c
commit 69d2c86766
1 changed files with 4 additions and 0 deletions
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4
net/ipv6/ip6mr.c
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@ -52,6 +52,8 @@
#include <net/ip6_checksum.h>
#include <linux/netconf.h>
#include <linux/nospec.h>
struct ip6mr_rule {
struct fib_rule common;
};
@ -1841,6 +1843,7 @@ int ip6mr_ioctl(struct sock *sk, int cmd, void __user *arg)
return -EFAULT;
if (vr.mifi >= mrt->maxvif)
return -EINVAL;
vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
read_lock(&mrt_lock);
vif = &mrt->vif_table[vr.mifi];
if (VIF_EXISTS(mrt, vr.mifi)) {
@ -1915,6 +1918,7 @@ int ip6mr_compat_ioctl(struct sock *sk, unsigned int cmd, void __user *arg)
return -EFAULT;
if (vr.mifi >= mrt->maxvif)
return -EINVAL;
vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
read_lock(&mrt_lock);
vif = &mrt->vif_table[vr.mifi];
if (VIF_EXISTS(mrt, vr.mifi)) {