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Subject[PATCH 4.4 14/88] ip6mr: Fix potential Spectre v1 vulnerability
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

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

[ Upstream commit 69d2c86766da2ded2b70281f1bf242cb0d58a778 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/ip6mr.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -72,6 +72,8 @@ struct mr6_table {
#endif
};

+#include <linux/nospec.h>
+
struct ip6mr_rule {
struct fib_rule common;
};
@@ -1871,6 +1873,7 @@ int ip6mr_ioctl(struct sock *sk, int cmd
return -EFAULT;
if (vr.mifi >= mrt->maxvif)
return -EINVAL;
+ vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
read_lock(&mrt_lock);
vif = &mrt->vif6_table[vr.mifi];
if (MIF_EXISTS(mrt, vr.mifi)) {
@@ -1945,6 +1948,7 @@ int ip6mr_compat_ioctl(struct sock *sk,
return -EFAULT;
if (vr.mifi >= mrt->maxvif)
return -EINVAL;
+ vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
read_lock(&mrt_lock);
vif = &mrt->vif6_table[vr.mifi];
if (MIF_EXISTS(mrt, vr.mifi)) {

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