CVE-2021-47506 nfsd: fix use-after-free due to delegation race

2024-05-2415:01:52

Linux

github.com

linux kernel

vulnerability

cve-2021-47506

nfsd

use-after-free

delegation race

list corruption

callback

AI Score

Confidence

Low

EPSS

Percentile

13.0%

SSVC

Exploitation

none

Automatable

Technical Impact

total

JSON

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

nfsd: fix use-after-free due to delegation race

A delegation break could arrive as soon as we’ve called vfs_setlease. A
delegation break runs a callback which immediately (in
nfsd4_cb_recall_prepare) adds the delegation to del_recall_lru. If we
then exit nfs4_set_delegation without hashing the delegation, it will be
freed as soon as the callback is done with it, without ever being
removed from del_recall_lru.

Symptoms show up later as use-after-free or list corruption warnings,
usually in the laundromat thread.

I suspect aba2072f4523 “nfsd: grant read delegations to clients holding
writes” made this bug easier to hit, but I looked as far back as v3.0
and it looks to me it already had the same problem. So I’m not sure
where the bug was introduced; it may have been there from the beginning.

CNA Affected

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "04a8d07f3d58",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "348714018139",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "33645d3e2272",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "2becaa990b93",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "e0759696de68",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "eeb0711801f5",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "148c816f10fd",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "1da177e4c3f4",
        "lessThan": "548ec0805c39",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "fs/nfsd/nfs4state.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "unaffected",
        "version": "4.4.296",
        "versionType": "custom",
        "lessThanOrEqual": "4.4.*"
      },
      {
        "status": "unaffected",
        "version": "4.9.294",
        "versionType": "custom",
        "lessThanOrEqual": "4.9.*"
      },
      {
        "status": "unaffected",
        "version": "4.14.259",
        "versionType": "custom",
        "lessThanOrEqual": "4.14.*"
      },
      {
        "status": "unaffected",
        "version": "4.19.222",
        "versionType": "custom",
        "lessThanOrEqual": "4.19.*"
      },
      {
        "status": "unaffected",
        "version": "5.4.168",
        "versionType": "custom",
        "lessThanOrEqual": "5.4.*"
      },
      {
        "status": "unaffected",
        "version": "5.10.85",
        "versionType": "custom",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.15.8",
        "versionType": "custom",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "5.16",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "fs/nfsd/nfs4state.c"
    ],
    "defaultStatus": "affected"
  }
]