Subject: CVE-2024-26999: serial/pmac_zilog: Remove flawed mitigation for rx irq flood

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

serial/pmac_zilog: Remove flawed mitigation for rx irq flood

The mitigation was intended to stop the irq completely. That may be
better than a hard lock-up but it turns out that you get a crash anyway
if you're using pmac_zilog as a serial console:

ttyPZ0: pmz: rx irq flood !
BUG: spinlock recursion on CPU#0, swapper/0

That's because the pr_err() call in pmz_receive_chars() results in
pmz_console_write() attempting to lock a spinlock already locked in
pmz_interrupt(). With CONFIG_DEBUG_SPINLOCK=y, this produces a fatal
BUG splat. The spinlock in question is the one in struct uart_port.

Even when it's not fatal, the serial port rx function ceases to work.
Also, the iteration limit doesn't play nicely with QEMU, as can be
seen in the bug report linked below.

A web search for other reports of the error message "pmz: rx irq flood"
didn't produce anything. So I don't think this code is needed any more.
Remove it.

The Linux kernel CVE team has assigned CVE-2024-26999 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 4.19.313 with commit 69a02273e288
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 5.4.275 with commit d679c816929d
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 5.10.216 with commit ab86cf6f8d24
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 5.15.157 with commit 7a3bbe41efa5
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.1.88 with commit bbaafbb4651f
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.6.29 with commit 52aaf1ff1462
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.8.8 with commit ca09dfc3cfdf
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.9 with commit 1be322644536

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-26999
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/tty/serial/pmac_zilog.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/69a02273e288011b521ee7c1f3ab2c23fda633ce
	https://git.kernel.org/stable/c/d679c816929d62af51c8e6d7fc0e165c9412d2f3
	https://git.kernel.org/stable/c/ab86cf6f8d24e63e9aca23da5108af1aa5483928
	https://git.kernel.org/stable/c/7a3bbe41efa55323b6ea3c35fa15941d4dbecdef
	https://git.kernel.org/stable/c/bbaafbb4651fede8d3c3881601ecaa4f834f9d3f
	https://git.kernel.org/stable/c/52aaf1ff14622a04148dbb9ccce6d9de5d534ea7
	https://git.kernel.org/stable/c/ca09dfc3cfdf89e6af3ac24e1c6c0be5c575a729
	https://git.kernel.org/stable/c/1be3226445362bfbf461c92a5bcdb1723f2e4907