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    Subject[PATCH 4.4 33/36] mpls, nospec: Sanitize array index in mpls_label_ok()
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Dan Williams <dan.j.williams@intel.com>

    commit 3968523f855050b8195134da951b87c20bd66130 upstream.

    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: "David S. Miller" <davem@davemloft.net>
    Cc: Eric W. Biederman <ebiederm@xmission.com>
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [bwh: Backported to 4.4:
    - mpls_label_ok() doesn't take an extack parameter
    - Drop change in mpls_getroute()]
    Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/mpls/af_mpls.c | 22 +++++++++++++---------
    1 file changed, 13 insertions(+), 9 deletions(-)

    --- a/net/mpls/af_mpls.c
    +++ b/net/mpls/af_mpls.c
    @@ -7,6 +7,7 @@
    #include <linux/if_arp.h>
    #include <linux/ipv6.h>
    #include <linux/mpls.h>
    +#include <linux/nospec.h>
    #include <linux/vmalloc.h>
    #include <net/ip.h>
    #include <net/dst.h>
    @@ -714,17 +715,20 @@ errout:
    return err;
    }

    -static bool mpls_label_ok(struct net *net, unsigned int index)
    +static bool mpls_label_ok(struct net *net, unsigned int *index)
    {
    + bool is_ok = true;
    +
    /* Reserved labels may not be set */
    - if (index < MPLS_LABEL_FIRST_UNRESERVED)
    - return false;
    + if (*index < MPLS_LABEL_FIRST_UNRESERVED)
    + is_ok = false;

    /* The full 20 bit range may not be supported. */
    - if (index >= net->mpls.platform_labels)
    - return false;
    + if (is_ok && *index >= net->mpls.platform_labels)
    + 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)
    @@ -745,7 +749,7 @@ static int mpls_route_add(struct mpls_ro
    index = find_free_label(net);
    }

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

    /* Append makes no sense with mpls */
    @@ -806,7 +810,7 @@ static int mpls_route_del(struct mpls_ro

    index = cfg->rc_label;

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

    mpls_route_update(net, index, NULL, &cfg->rc_nlinfo);
    @@ -1166,7 +1170,7 @@ static int rtm_to_route_config(struct sk
    goto errout;

    if (!mpls_label_ok(cfg->rc_nlinfo.nl_net,
    - cfg->rc_label))
    + &cfg->rc_label))
    goto errout;
    break;
    }

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