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Subject[PATCH] mpls, nospec: Sanitize array index in mpls_label_ok()
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mpls_label_ok() validates that the 'platform_label' array index from a
userspace netlink message payload is valid. Under speculation the
mpls_label_ok() result may not resolve in the CPU pipeline until after
the index is used to access an array element. Sanitize the index to zero
to prevent userspace-controlled arbitrary out-of-bounds speculation, a
precursor for a speculative execution side channel vulnerability.

Cc: <stable@vger.kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
net/mpls/af_mpls.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index 8ca9915befc8..aae3565c3a92 100644
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -8,6 +8,7 @@
#include <linux/ipv6.h>
#include <linux/mpls.h>
#include <linux/netconf.h>
+#include <linux/nospec.h>
#include <linux/vmalloc.h>
#include <linux/percpu.h>
#include <net/ip.h>
@@ -935,24 +936,27 @@ static int mpls_nh_build_multi(struct mpls_route_config *cfg,
return err;
}

-static bool mpls_label_ok(struct net *net, unsigned int index,
+static bool mpls_label_ok(struct net *net, unsigned int *index,
struct netlink_ext_ack *extack)
{
+ bool is_ok = true;
+
/* Reserved labels may not be set */
- if (index < MPLS_LABEL_FIRST_UNRESERVED) {
+ if (*index < MPLS_LABEL_FIRST_UNRESERVED) {
NL_SET_ERR_MSG(extack,
"Invalid label - must be MPLS_LABEL_FIRST_UNRESERVED or higher");
- return false;
+ is_ok = false;
}

/* The full 20 bit range may not be supported. */
- if (index >= net->mpls.platform_labels) {
+ if (is_ok && *index >= net->mpls.platform_labels) {
NL_SET_ERR_MSG(extack,
"Label >= configured maximum in platform_labels");
- return false;
+ is_ok = false;
}

- return true;
+ *index = array_index_nospec(*index, net->mpls.platform_labels);
+ return is_ok;
}

static int mpls_route_add(struct mpls_route_config *cfg,
@@ -975,7 +979,7 @@ static int mpls_route_add(struct mpls_route_config *cfg,
index = find_free_label(net);
}

- if (!mpls_label_ok(net, index, extack))
+ if (!mpls_label_ok(net, &index, extack))
goto errout;

/* Append makes no sense with mpls */
@@ -1052,7 +1056,7 @@ static int mpls_route_del(struct mpls_route_config *cfg,

index = cfg->rc_label;

- if (!mpls_label_ok(net, index, extack))
+ if (!mpls_label_ok(net, &index, extack))
goto errout;

mpls_route_update(net, index, NULL, &cfg->rc_nlinfo);
@@ -1810,7 +1814,7 @@ static int rtm_to_route_config(struct sk_buff *skb,
goto errout;

if (!mpls_label_ok(cfg->rc_nlinfo.nl_net,
- cfg->rc_label, extack))
+ &cfg->rc_label, extack))
goto errout;
break;
}
@@ -2137,7 +2141,7 @@ static int mpls_getroute(struct sk_buff *in_skb, struct nlmsghdr *in_nlh,
goto errout;
}

- if (!mpls_label_ok(net, in_label, extack)) {
+ if (!mpls_label_ok(net, &in_label, extack)) {
err = -EINVAL;
goto errout;
}
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