CVE-2024-44951

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

serial: sc16is7xx: fix TX fifo corruption

Sometimes, when a packet is received on channel A at almost the same time

as a packet is about to be transmitted on channel B, we observe with a

logic analyzer that the received packet on channel A is transmitted on

channel B. In other words, the Tx buffer data on channel B is corrupted

with data from channel A.

The problem appeared since commit 4409df5866b7 ("serial: sc16is7xx: change

EFR lock to operate on each channels"), which changed the EFR locking to

operate on each channel instead of chip-wise.

This commit has introduced a regression, because the EFR lock is used not

only to protect the EFR registers access, but also, in a very obscure and

undocumented way, to protect access to the data buffer, which is shared by

the Tx and Rx handlers, but also by each channel of the IC.

Fix this regression first by switching to kfifo_out_linear_ptr() in

sc16is7xx_handle_tx() to eliminate the need for a shared Rx/Tx buffer.

Secondly, replace the chip-wise Rx buffer with a separate Rx buffer for

each channel.