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    Subject[PATCH 5.8 115/124] net/core: check length before updating Ethertype in skb_mpls_{push,pop}
    Date
    From: Guillaume Nault <gnault@redhat.com>

    commit 4296adc3e32f5d544a95061160fe7e127be1b9ff upstream.

    Openvswitch allows to drop a packet's Ethernet header, therefore
    skb_mpls_push() and skb_mpls_pop() might be called with ethernet=true
    and mac_len=0. In that case the pointer passed to skb_mod_eth_type()
    doesn't point to an Ethernet header and the new Ethertype is written at
    unexpected locations.

    Fix this by verifying that mac_len is big enough to contain an Ethernet
    header.

    Fixes: fa4e0f8855fc ("net/sched: fix corrupted L2 header with MPLS 'push' and 'pop' actions")
    Signed-off-by: Guillaume Nault <gnault@redhat.com>
    Acked-by: Davide Caratti <dcaratti@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/core/skbuff.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/net/core/skbuff.c
    +++ b/net/core/skbuff.c
    @@ -5621,7 +5621,7 @@ int skb_mpls_push(struct sk_buff *skb, _
    lse->label_stack_entry = mpls_lse;
    skb_postpush_rcsum(skb, lse, MPLS_HLEN);

    - if (ethernet)
    + if (ethernet && mac_len >= ETH_HLEN)
    skb_mod_eth_type(skb, eth_hdr(skb), mpls_proto);
    skb->protocol = mpls_proto;

    @@ -5661,7 +5661,7 @@ int skb_mpls_pop(struct sk_buff *skb, __
    skb_reset_mac_header(skb);
    skb_set_network_header(skb, mac_len);

    - if (ethernet) {
    + if (ethernet && mac_len >= ETH_HLEN) {
    struct ethhdr *hdr;

    /* use mpls_hdr() to get ethertype to account for VLANs. */

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