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    Subject[PATCH 5.11 011/306] net: avoid infinite loop in mpls_gso_segment when mpls_hlen == 0
    Date
    From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    From: Balazs Nemeth <bnemeth@redhat.com>

    commit d348ede32e99d3a04863e9f9b28d224456118c27 upstream.

    A packet with skb_inner_network_header(skb) == skb_network_header(skb)
    and ETH_P_MPLS_UC will prevent mpls_gso_segment from pulling any headers
    from the packet. Subsequently, the call to skb_mac_gso_segment will
    again call mpls_gso_segment with the same packet leading to an infinite
    loop. In addition, ensure that the header length is a multiple of four,
    which should hold irrespective of the number of stacked labels.

    Signed-off-by: Balazs Nemeth <bnemeth@redhat.com>
    Acked-by: Willem de Bruijn <willemb@google.com>
    Reviewed-by: David Ahern <dsahern@kernel.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/mpls/mpls_gso.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/net/mpls/mpls_gso.c
    +++ b/net/mpls/mpls_gso.c
    @@ -14,6 +14,7 @@
    #include <linux/netdev_features.h>
    #include <linux/netdevice.h>
    #include <linux/skbuff.h>
    +#include <net/mpls.h>

    static struct sk_buff *mpls_gso_segment(struct sk_buff *skb,
    netdev_features_t features)
    @@ -27,6 +28,8 @@ static struct sk_buff *mpls_gso_segment(

    skb_reset_network_header(skb);
    mpls_hlen = skb_inner_network_header(skb) - skb_network_header(skb);
    + if (unlikely(!mpls_hlen || mpls_hlen % MPLS_HLEN))
    + goto out;
    if (unlikely(!pskb_may_pull(skb, mpls_hlen)))
    goto out;


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