CVE-2021-47282 spi: bcm2835: Fix out-of-bounds access with more than 4 slaves

2024-05-2114:20:08

Linux

github.com

linux kernel

vulnerability

bcm2835

out-of-bounds access

spi

device tree

gpio

backportable

AI Score

Confidence

High

EPSS

Percentile

15.5%

SSVC

Exploitation

none

Automatable

Technical Impact

partial

JSON

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.

CNA Affected

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "571e31fa60b3",
        "lessThan": "b5502580cf95",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "571e31fa60b3",
        "lessThan": "82a8ffba54d3",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "571e31fa60b3",
        "lessThan": "01415ff85a24",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "571e31fa60b3",
        "lessThan": "13817d466eb8",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "drivers/spi/spi-bcm2835.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "5.4"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "5.4",
        "versionType": "custom"
      },
      {
        "status": "unaffected",
        "version": "5.4.126",
        "versionType": "custom",
        "lessThanOrEqual": "5.4.*"
      },
      {
        "status": "unaffected",
        "version": "5.10.44",
        "versionType": "custom",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.12.11",
        "versionType": "custom",
        "lessThanOrEqual": "5.12.*"
      },
      {
        "status": "unaffected",
        "version": "5.13",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "drivers/spi/spi-bcm2835.c"
    ],
    "defaultStatus": "affected"
  }
]