CVE-2026-74654: serial: 8250_dma: Clear stale RX state on shutdown

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

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

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

serial: 8250_dma: Clear stale RX state on shutdown

serial8250_release_dma() terminates RX DMA and releases the channel, but
leaves rx_running set.  If the port is closed while an RX transfer is
active, the stale state remains while rxchan is NULL until the channel is
requested again on the next open.

The DesignWare BUSY workaround added by commit a7b9ce39fbe4
("serial: 8250_dw: Ensure BUSY is deasserted") calls
serial8250_rx_dma_flush() from the LCR write path during startup.  This
happens before serial8250_request_dma() obtains a new RX channel.  On
reopen, the stale rx_running state therefore makes the flush path pass a
NULL channel to dmaengine_pause(), causing a kernel Oops.

Clear rx_running after terminating RX DMA, matching the TX cleanup.  Also
make the flush helper return if the DMA object or RX channel is not
available so startup and teardown paths cannot pass a NULL channel to the
DMAengine API.

The Linux kernel CVE team has assigned CVE-2026-74654 to this issue.


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

	Issue introduced in 3.19 with commit 0fcb7901f9d61a325b4c5b88c600383bcbeb97fe and fixed in 5.10.265 with commit bf4fb620e02962b2b52500a4b3d8420f351eb46a
	Issue introduced in 3.19 with commit 0fcb7901f9d61a325b4c5b88c600383bcbeb97fe and fixed in 5.15.216 with commit e10f06ee050a08930e2339b6fec7148fd0b2a8f6
	Issue introduced in 3.19 with commit 0fcb7901f9d61a325b4c5b88c600383bcbeb97fe and fixed in 6.1.183 with commit d06cfb1add4a2d5b393e9e31f49ebbd168beea49
	Issue introduced in 3.19 with commit 0fcb7901f9d61a325b4c5b88c600383bcbeb97fe and fixed in 6.6.152 with commit e7a5d792cf64a2096e18f1d573cc3d01cba15e92
	Issue introduced in 3.19 with commit 0fcb7901f9d61a325b4c5b88c600383bcbeb97fe and fixed in 6.12.104 with commit 9f2444f4c0e4b06f61bae38da87c9c94c78efa86
	Issue introduced in 3.19 with commit 0fcb7901f9d61a325b4c5b88c600383bcbeb97fe and fixed in 6.18.45 with commit ae05d9e50b6b9f246c110b3bdc03676145c2d0d4
	Issue introduced in 3.19 with commit 0fcb7901f9d61a325b4c5b88c600383bcbeb97fe and fixed in 7.1.9 with commit e7e3cc6709caa49d1d6ce6c1f7cb305e38675cc9
	Issue introduced in 3.19 with commit 0fcb7901f9d61a325b4c5b88c600383bcbeb97fe and fixed in 7.2 with commit e2fe6a0efecbef00e3ecc2db64dd5afa8c212b41

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-2026-74654
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/8250/8250_dma.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/bf4fb620e02962b2b52500a4b3d8420f351eb46a
	https://git.kernel.org/stable/c/e10f06ee050a08930e2339b6fec7148fd0b2a8f6
	https://git.kernel.org/stable/c/d06cfb1add4a2d5b393e9e31f49ebbd168beea49
	https://git.kernel.org/stable/c/e7a5d792cf64a2096e18f1d573cc3d01cba15e92
	https://git.kernel.org/stable/c/9f2444f4c0e4b06f61bae38da87c9c94c78efa86
	https://git.kernel.org/stable/c/ae05d9e50b6b9f246c110b3bdc03676145c2d0d4
	https://git.kernel.org/stable/c/e7e3cc6709caa49d1d6ce6c1f7cb305e38675cc9
	https://git.kernel.org/stable/c/e2fe6a0efecbef00e3ecc2db64dd5afa8c212b41