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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

Gustavo A. R. Silva committed 7 years ago

Commit 69d2c861 parent 51367e41 file · +4 −0Browse files

Unified · Split

net/ipv6/ip6mr.c+4−0
@@ -52,6 +52,8 @@ · 51 unmodified lines
52#include <net/ip6_checksum.h>52#include <net/ip6_checksum.h>
53#include <linux/netconf.h>53#include <linux/netconf.h>
54 54
55#include <linux/nospec.h>
56
55struct ip6mr_rule {57struct ip6mr_rule {
56 struct fib_rule common;58 struct fib_rule common;
57};59};
@@ -1841,6 +1843,7 @@ int ip6mr_ioctl(struct sock *sk, int cmd, void __user *arg) · 1783 unmodified lines
1841 return -EFAULT;1843 return -EFAULT;
1842 if (vr.mifi >= mrt->maxvif)1844 if (vr.mifi >= mrt->maxvif)
1843 return -EINVAL;1845 return -EINVAL;
1846 vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
1844 read_lock(&mrt_lock);1847 read_lock(&mrt_lock);
1845 vif = &mrt->vif_table[vr.mifi];1848 vif = &mrt->vif_table[vr.mifi];
1846 if (VIF_EXISTS(mrt, vr.mifi)) {1849 if (VIF_EXISTS(mrt, vr.mifi)) {
@@ -1915,6 +1918,7 @@ int ip6mr_compat_ioctl(struct sock *sk, unsigned int cmd, void __user *arg) · 68 unmodified lines
1915 return -EFAULT;1918 return -EFAULT;
1916 if (vr.mifi >= mrt->maxvif)1919 if (vr.mifi >= mrt->maxvif)
1917 return -EINVAL;1920 return -EINVAL;
1921 vr.mifi = array_index_nospec(vr.mifi, mrt->maxvif);
1918 read_lock(&mrt_lock);1922 read_lock(&mrt_lock);
1919 vif = &mrt->vif_table[vr.mifi];1923 vif = &mrt->vif_table[vr.mifi];
1920 if (VIF_EXISTS(mrt, vr.mifi)) {1924 if (VIF_EXISTS(mrt, vr.mifi)) {