CVE-2022-49147 — block: Fix the maximum minor value is blk_alloc_ext_minor()

Affected: Linux

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

block: Fix the maximum minor value is blk_alloc_ext_minor()

ida_alloc_range(..., min, max, ...) returns values from min to max, inclusive.

So, NR_EXT_DEVT is a valid idx returned by blk_alloc_ext_minor().

This is an issue because in device_add_disk(), this value is used in: ddev->devt = MKDEV(disk->major, disk->first_minor); and NR_EXT_DEVT is '(1 << MINORBITS)'.

So, should 'disk->first_minor' be NR_EXT_DEVT, it would overflow.

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CVE-2022-49147 — block: Fix the maximum minor value is blk_alloc_ext_minor()