Use After Free Affecting kernel-debuginfo package, versions <0:4.14.238-182.421.amzn2

Note: Versions mentioned in the description apply only to the upstream kernel-debuginfo package and not the kernel-debuginfo package as distributed by Amazon-Linux. See How to fix? for Amazon-Linux:2 relevant fixed versions and status.

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

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

In emac_mac_tx_buf_send, it calls emac_tx_fill_tpd(..,skb,..). If some error happens in emac_tx_fill_tpd(), the skb will be freed via dev_kfree_skb(skb) in error branch of emac_tx_fill_tpd(). But the freed skb is still used via skb->len by netdev_sent_queue(,skb->len).

As i observed that emac_tx_fill_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.

• http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-47013
• https://git.kernel.org/stable/c/16d8c44be52e3650917736d45f5904384a9da834
• https://git.kernel.org/stable/c/55fcdd1258faaecca74b91b88cc0921f9edd775d
• https://git.kernel.org/stable/c/6d72e7c767acbbdd44ebc7d89c6690b405b32b57
• https://git.kernel.org/stable/c/8c06f34785068b87e2b560534c77c163d6c6dca7
• https://git.kernel.org/stable/c/9dc373f74097edd0e35f3393d6248eda8d1ba99d
• https://git.kernel.org/stable/c/c7f75d11fe72913d2619f97b2334b083cd7bb955
• https://git.kernel.org/stable/c/dc1b438a35773d030be0ee80d9c635c3e558a322
• https://git.kernel.org/stable/c/e407495ba6788a67d1bd41714158c079e340879b