CVE-2026-68184: cdrom: fix stack out-of-bounds read in CDROMVOLCTRL

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

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

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

cdrom: fix stack out-of-bounds read in CDROMVOLCTRL

mmc_ioctl_cdrom_volume() first reads the audio control mode page into a
32-byte stack buffer with cgc->buflen set to 24.  If the device reports a
block descriptor, the function increases cgc->buflen to include that
descriptor and reads the page again.

For CDROMVOLCTRL, the function then builds a MODE SELECT parameter list
by moving cgc->buffer forward by offset - 8 bytes.  This drops the block
descriptor from the outgoing payload and leaves a new 8-byte mode
parameter header in front of the audio control page.  However, cgc->buflen
is left unchanged.

With a standard 8-byte block descriptor, cgc->buffer points at buffer + 8
but cgc->buflen remains 32.  cdrom_mode_select() therefore asks the low
level packet path to write 32 bytes from that adjusted pointer, reading 8
bytes past the end of the 32-byte stack buffer.

This is not hit by CDROMVOLREAD, and CDROMVOLCTRL only triggers it on
drives that return a non-zero block descriptor length, which helps explain
why it has gone unnoticed.  The overread is also sent to the device as
extra MODE SELECT payload, so it may not produce an obvious local failure.

Reduce cgc->buflen by the same amount as the buffer pointer adjustment so
the MODE SELECT transfer covers only the intended parameter list.

The Linux kernel CVE team has assigned CVE-2026-68184 to this issue.


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

	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.6.148 with commit 7344c84e32413e5c8832f74b8a612b0194e5c051
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.12.101 with commit 35b68e24c5a69fa4545f46f05f6c849223034cb6
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 6.18.42 with commit d43c5c0c935522deae7339e0c2399365f3bf0016
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.1.6 with commit f3e2715a150066f09aa82c30fa983fb184ad6dd5
	Issue introduced in 2.6.12 with commit 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and fixed in 7.2-rc5 with commit b27e195d4db8dea263050bdbeb11881b2999c9c6

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-2026-68184
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/cdrom/cdrom.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/7344c84e32413e5c8832f74b8a612b0194e5c051
	https://git.kernel.org/stable/c/35b68e24c5a69fa4545f46f05f6c849223034cb6
	https://git.kernel.org/stable/c/d43c5c0c935522deae7339e0c2399365f3bf0016
	https://git.kernel.org/stable/c/f3e2715a150066f09aa82c30fa983fb184ad6dd5
	https://git.kernel.org/stable/c/b27e195d4db8dea263050bdbeb11881b2999c9c6