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CVE-2021-47282

Disclosure Date: May 21, 2024 •
CVE-2021-47282
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Description

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

spi: bcm2835: Fix out-of-bounds access with more than 4 slaves

Commit 571e31fa60b3 (“spi: bcm2835: Cache CS register value for
–>prepare_message()”) limited the number of slaves to 3 at compile-time.
The limitation was necessitated by a statically-sized array prepare_cs[]
in the driver private data which contains a per-slave register value.

The commit sought to enforce the limitation at run-time by setting the
controller’s num_chipselect to 3: Slaves with a higher chipselect are
rejected by spi_add_device().

However the commit neglected that num_chipselect only limits the number
of native chipselects. If GPIO chipselects are specified in the
device tree for more than 3 slaves, num_chipselect is silently raised by
of_spi_get_gpio_numbers() and the result are out-of-bounds accesses to
the statically-sized array prepare_cs[].

As a bandaid fix which is backportable to stable, raise the number of
allowed slaves to 24 (which “ought to be enough for anybody”), enforce
the limitation on slave –>setup and revert num_chipselect to 3 (which is
the number of native chipselects supported by the controller).
An upcoming for-next commit will allow an arbitrary number of slaves.

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CVSS V3 Severity and Metrics
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General Information

Offensive Application
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Utility Class
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Ports
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OS
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Vulnerable Versions
Linux b5502580cf95
Linux not down converted
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Vendors

  • Linux

Products

  • Linux
Technical Analysis