CVE-2026-64336: USB: serial: keyspan_pda: fix information leak

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

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

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

USB: serial: keyspan_pda: fix information leak

The write() callback is supposed to return the number of characters
accepted or a negative errno. Since the addition of write fifo support
the keyspan_pda implementation will however return the number characters
submitted to the device if the write urb is not already in use. If this
number is larger than the number of characters passed to write(), the
line discipline continues writing data from beyond the tty write buffer.

Fix the information leak by making sure that keyspan_pda_write_start()
returns zero on success as intended.

The Linux kernel CVE team has assigned CVE-2026-64336 to this issue.


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

	Issue introduced in 5.11 with commit 034e38e8f68767fb5438ae3e608ee82919674177 and fixed in 5.15.212 with commit b069b7029862fafaff331d4c664d97d4ae828d6d
	Issue introduced in 5.11 with commit 034e38e8f68767fb5438ae3e608ee82919674177 and fixed in 6.1.178 with commit e52ca411f50539ff1d0c877b9312771ca8a858c1
	Issue introduced in 5.11 with commit 034e38e8f68767fb5438ae3e608ee82919674177 and fixed in 6.6.145 with commit 2f7a6b8ab3845bd1da02604f1a874b52a4555a72
	Issue introduced in 5.11 with commit 034e38e8f68767fb5438ae3e608ee82919674177 and fixed in 6.12.96 with commit e1494191a3aac665d3a2fce16169a97c346253ec
	Issue introduced in 5.11 with commit 034e38e8f68767fb5438ae3e608ee82919674177 and fixed in 6.18.39 with commit cf6ca0aefae03958cfb5b189b0adbfb25c06bfac
	Issue introduced in 5.11 with commit 034e38e8f68767fb5438ae3e608ee82919674177 and fixed in 7.1.4 with commit d4b12b6b395e43a2b1d80be3745631fcaa9c047b
	Issue introduced in 5.11 with commit 034e38e8f68767fb5438ae3e608ee82919674177 and fixed in 7.2-rc3 with commit 6bfc8d01ac4068eced509f8fc74d0cd205e4dcec

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-2026-64336
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/usb/serial/keyspan_pda.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/b069b7029862fafaff331d4c664d97d4ae828d6d
	https://git.kernel.org/stable/c/e52ca411f50539ff1d0c877b9312771ca8a858c1
	https://git.kernel.org/stable/c/2f7a6b8ab3845bd1da02604f1a874b52a4555a72
	https://git.kernel.org/stable/c/e1494191a3aac665d3a2fce16169a97c346253ec
	https://git.kernel.org/stable/c/cf6ca0aefae03958cfb5b189b0adbfb25c06bfac
	https://git.kernel.org/stable/c/d4b12b6b395e43a2b1d80be3745631fcaa9c047b
	https://git.kernel.org/stable/c/6bfc8d01ac4068eced509f8fc74d0cd205e4dcec