CVE-2021-47013

In the Linux kernel, the following vulnerability has been resolved:

net:emac/emac-mac: Fix a use after free in emacmactxbufsend

In emacmactxbufsend, it calls emactxfilltpd(..,skb,..). If some error happens in emactxfilltpd(), the skb will be freed via devkfreeskb(skb) in error branch of emactxfilltpd(). But the freed skb is still used via skb->len by netdevsent_queue(,skb->len).

As i observed that emactxfill_tpd() haven't modified the value of skb->len, thus my patch assigns skb->len to 'len' before the possible free and use 'len' instead of skb->len later.