CVE-2021-47587

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

net: systemport: Add global locking for descriptor lifecycle

The descriptor list is a shared resource across all of the transmit queues, and

the locking mechanism used today only protects concurrency across a given

transmit queue between the transmit and reclaiming. This creates an opportunity

for the SYSTEMPORT hardware to work on corrupted descriptors if we have

multiple producers at once which is the case when using multiple transmit

queues.

This was particularly noticeable when using multiple flows/transmit queues and

it showed up in interesting ways in that UDP packets would get a correct UDP

header checksum being calculated over an incorrect packet length. Similarly TCP

packets would get an equally correct checksum computed by the hardware over an

incorrect packet length.

The SYSTEMPORT hardware maintains an internal descriptor list that it re-arranges

when the driver produces a new descriptor anytime it writes to the

WRITE_PORT_{HI,LO} registers, there is however some delay in the hardware to

re-organize its descriptors and it is possible that concurrent TX queues

eventually break this internal allocation scheme to the point where the

length/status part of the descriptor gets used for an incorrect data buffer.

The fix is to impose a global serialization for all TX queues in the short

section where we are writing to the WRITE_PORT_{HI,LO} registers which solves

the corruption even with multiple concurrent TX queues being used.