CVE-2026-68449: ata: sata_dwc_460ex: fix infinite loop in NCQ tag completion bit-scanning

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

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

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

ata: sata_dwc_460ex: fix infinite loop in NCQ tag completion bit-scanning

The hand-rolled bit-scanning loop in the NCQ completion path has an
infinite loop bug.  When tag_mask has only high bits set (e.g.
0x80000000), the inner while loop left-shifts tag_mask until it
overflows to 0.  At that point !(0 & 1) is always true and 0 <<= 1
stays 0, causing an infinite loop in hardirq context with a spinlock
held.

Replace the open-coded bit-scanning with __ffs() which correctly
finds the least significant set bit and is bounded by the width of
the argument.

The Linux kernel CVE team has assigned CVE-2026-68449 to this issue.


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

	Issue introduced in 2.6.36 with commit 62936009f35a6659cc3ebe0d90c754182d60da73 and fixed in 6.6.148 with commit 4c6e64cae2b2dab32ad9099faa339f6a72c0ce16
	Issue introduced in 2.6.36 with commit 62936009f35a6659cc3ebe0d90c754182d60da73 and fixed in 6.12.101 with commit 8c5de0d8ab6824cfdadcbbe1be4c6c9d9f4c1f80
	Issue introduced in 2.6.36 with commit 62936009f35a6659cc3ebe0d90c754182d60da73 and fixed in 6.18.42 with commit 1842d45f461a78988254631893329bdf4596e954
	Issue introduced in 2.6.36 with commit 62936009f35a6659cc3ebe0d90c754182d60da73 and fixed in 7.1.6 with commit 29b916d3556bd12a95be7c56ca391b8cd572f8be
	Issue introduced in 2.6.36 with commit 62936009f35a6659cc3ebe0d90c754182d60da73 and fixed in 7.2-rc4 with commit c2130f6553f4a5cbdc259de069600117a995f197

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-2026-68449
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/ata/sata_dwc_460ex.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/4c6e64cae2b2dab32ad9099faa339f6a72c0ce16
	https://git.kernel.org/stable/c/8c5de0d8ab6824cfdadcbbe1be4c6c9d9f4c1f80
	https://git.kernel.org/stable/c/1842d45f461a78988254631893329bdf4596e954
	https://git.kernel.org/stable/c/29b916d3556bd12a95be7c56ca391b8cd572f8be
	https://git.kernel.org/stable/c/c2130f6553f4a5cbdc259de069600117a995f197