CVE-2022-50483 — net: enetc: avoid buffer leaks on xdp_do_redirect() failure

Affected: Linux

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

net: enetc: avoid buffer leaks on xdp_do_redirect() failure

Before enetc_clean_rx_ring_xdp() calls xdp_do_redirect(), each software BD in the RX ring between index orig_i and i can have one of 2 refcount values on its page.

We are the owner of the current buffer that is being processed, so the refcount will be at least 1.

If the current owner of the buffer at the diametrically opposed index in the RX ring (i.o.w, the other half of this page) has not yet called kfree(), this page's refcount could even be 2.

enetc_page_reusable() in enetc_flip_rx_buff() tests for the page refcount against 1, and [ if it's 2 ] does not attempt to reuse it.

But if enetc_flip_rx_buff() is put after the xdp_do_redirect() call, the page refcount can have one of 3 values. It can also be 0, if there is no owner of the other page half, and xdp_do_redirect() for this buffer ran so far that it triggered a flush of the devmap/cpumap bulk queue, and the consumers of those bulk queues also freed the buffer, all by the time xdp_do_redirect() returns the execution back to enetc.

This is the reason why enetc_flip_rx_buff() is called before xdp_do_redirect(), but there is a big flaw with that reasoning: enetc_flip_rx_buff() will set rx_swbd->page = NULL on both sides of the enetc_page_reusable() branch, and if xdp_do_redirect() returns an error, we call enetc_xdp_free(), which does not deal gracefully with that.

In fact, what happens i…

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CVE-2022-50483 — net: enetc: avoid buffer leaks on xdp_do_redirect() failure