CVE-2021-47282: linux kernel Memory Corruption — Fix

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 v3.1 Score

7.8

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Weakness Type (CWE)

CWE-787 Out-of-bounds Write

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.4 — 5.4.126
linux	linux_kernel	5.5 — 5.10.44
linux	linux_kernel	5.11 — 5.12.11
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/01415ff85a24308059e06ca3e97fd7bf75648690 https://git.kernel.org/stable/c/13817d466eb8713a1ffd254f537402f091d48444 https://git.kernel.org/stable/c/82a8ffba54d31e97582051cb56ba1f988018681e https://git.kernel.org/stable/c/b5502580cf958b094f3b69dfe4eece90eae01fbc https://git.kernel.org/stable/c/01415ff85a24308059e06ca3e97fd7bf75648690 https://git.kernel.org/stable/c/13817d466eb8713a1ffd254f537402f091d48444 https://git.kernel.org/stable/c/82a8ffba54d31e97582051cb56ba1f988018681e https://git.kernel.org/stable/c/b5502580cf958b094f3b69dfe4eece90eae01fbc

Frequently Asked Questions

What is CVE-2021-47282? +

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. It has a CVSS v3.1 base score of 7.8 (HIGH).

How severe is CVE-2021-47282? +

CVE-2021-47282 has a CVSS v3.1 score of 7.8 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2021-47282? +

CVE-2021-47282 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2021-47282? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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