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

2024-02-2709:44:02

Linux

www.cve.org

linux kernel

binder

vulnerability

fix

async transactions

buffer size

security issue

accounting

kernel structure

0-length payloads

5.5 Medium

AI Score

Confidence

High

0.0004 Low

EPSS

Percentile

10.4%

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

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