CVE-2021-46935 binder: fix async_free_space accounting for empty parcels

2024-02-2709:44:02

Linux

github.com

linux kernel

binder

vulnerability fix

async_free_space

0-length data payloads

async transaction

AI Score

6.8

Confidence

Low

SSVC

Exploitation

none

Automatable

Technical Impact

partial

JSON

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

binder: fix async_free_space accounting for empty parcels

In 4.13, commit 74310e06be4d (“android: binder: Move buffer out of area shared with user space”)
fixed a kernel structure visibility issue. As part of that patch,
sizeof(void *) was used as the buffer size for 0-length data payloads so
the driver could detect abusive clients sending 0-length asynchronous
transactions to a server by enforcing limits on async_free_size.

Unfortunately, on the “free” side, the accounting of async_free_space
did not add the sizeof(void *) back. The result was that up to 8-bytes of
async_free_space were leaked on every async transaction of 8-bytes or
less. These small transactions are uncommon, so this accounting issue
has gone undetected for several years.

The fix is to use “buffer_size” (the allocated buffer size) instead of
“size” (the logical buffer size) when updating the async_free_space
during the free operation. These are the same except for this
corner case of asynchronous transactions with payloads < 8 bytes.

CNA Affected

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "74310e06be4d",
        "lessThan": "2d2df539d052",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "74310e06be4d",
        "lessThan": "7c7064402609",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "74310e06be4d",
        "lessThan": "103b16a8c51f",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "74310e06be4d",
        "lessThan": "1cb8444f3114",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "74310e06be4d",
        "lessThan": "17691bada6b2",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "74310e06be4d",
        "lessThan": "cfd0d84ba28c",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "drivers/android/binder_alloc.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "4.14"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "4.14",
        "versionType": "custom"
      },
      {
        "status": "unaffected",
        "version": "4.14.261",
        "versionType": "custom",
        "lessThanOrEqual": "4.14.*"
      },
      {
        "status": "unaffected",
        "version": "4.19.224",
        "versionType": "custom",
        "lessThanOrEqual": "4.19.*"
      },
      {
        "status": "unaffected",
        "version": "5.4.170",
        "versionType": "custom",
        "lessThanOrEqual": "5.4.*"
      },
      {
        "status": "unaffected",
        "version": "5.10.90",
        "versionType": "custom",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.15.13",
        "versionType": "custom",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "5.16",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "drivers/android/binder_alloc.c"
    ],
    "defaultStatus": "affected"
  }
]