regulator: ltc3676: don't read the write-only HRST and CLIRQ registers

Overview

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

regulator: ltc3676: don't read the write-only HRST and CLIRQ registers

HRST (0x1e) and CLIRQ (0x1f) are write-only command strobes. Writing HRST triggers a hard reset of the chip and writing CLIRQ clears the interrupt; reading them returns nothing useful, and the read itself fires the command.

The result is that a plain register dump resets the board:

cat /sys/kernel/debug/regmap/2-003c/registers

walks every readable register, hits HRST, and the board reboots.

Split the callback back in two so HRST and CLIRQ stay writable but are no longer readable. The readable range is left unchanged (LTC3676_BUCK1 ... LTC3676_IRQSTAT).

Affected

• Linux >= 37b918a034feda1b1ef404acf003812f37ab8da2 < fd376d83741118e0212f0da985889c1a98d9c827
• Linux >= 37b918a034feda1b1ef404acf003812f37ab8da2 < 1fb0d58fd363b439b4faf08a16ee6ae38b575cd4
• Linux >= 37b918a034feda1b1ef404acf003812f37ab8da2 < 199a62d70314d21f06a9a6faaa3ef54d0404910c
• Linux >= 37b918a034feda1b1ef404acf003812f37ab8da2 < ca5d85335a8fa6e87b45629f1a07b412482cab17
• Linux >= 37b918a034feda1b1ef404acf003812f37ab8da2 < 28c2388ee24cdbefbcc458fa41ef7bffaaa1cc83
• Linux 4.9

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.