Re: [PATCH v2] net/e1000e_core: adjust count if RDH exceeds RDT in e1000e_ring_advance()

[Jason Wang <jasowang@redhat.com>]

On 2020/11/13 下午6:31, Mauro Matteo Cascella wrote:
> The e1000e_write_packet_to_guest() function iterates over a set of
> receive descriptors by advancing rx descriptor head register (RDH) from
> its initial value to rx descriptor tail register (RDT). The check in
> e1000e_ring_empty() is responsible for detecting whether RDH has reached
> RDT, terminating the loop if that's the case. Additional checks have
> been added in the past to deal with bogus values submitted by the guest
> to prevent possible infinite loop. This is done by "wrapping around" RDH
> at some point and detecting whether it assumes the original value during
> the loop.
>
> However, when e1000e is configured to use the packet split feature, RDH is
> incremented by two instead of one, as the packet split descriptors are
> 32 bytes while regular descriptors are 16 bytes. A malicious or buggy
> guest may set RDT to an odd value and transmit only null RX descriptors.
> This corner case would prevent RDH from ever matching RDT, leading to an
> infinite loop. This patch adds a check in e1000e_ring_advance() to make sure
> RDH does not exceed RDT in a single incremental step, adjusting the count
> value accordingly.


Can this patch solve this issue in another way?

https://patchew.org/QEMU/20201111130636.2208620-1-ppandit@redhat.com/

Thanks