aio: fix use-after-free due to missing POLLFREE handling

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2021-47505
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2024-05-24 15:15:11 UTC
Updated2026-08-04 10:17:06 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: aio: fix use-after-free due to missing POLLFREE handling signalfd_poll() and binder_poll() are special in that they use a waitqueue whose lifetime is the current task, rather than the struct file as is normally the case. This is okay for blocking polls, since a blocking poll occurs within one task; however, non-blocking polls require another solution. This solution is for the queue to be cleared before it is freed, by sending a POLLFREE notification to all waiters. Unfortunately, only eventpoll handles POLLFREE. A second type of non-blocking poll, aio poll, was added in kernel v4.18, and it doesn't handle POLLFREE. This allows a use-after-free to occur if a signalfd or binder fd is polled with aio poll, and the waitqueue gets freed. Fix this by making aio poll handle POLLFREE. A patch by Ramji Jiyani <[email protected]> (https://lore.kernel.org/r/[email protected]) tried to do this by making aio_poll_wake() always complete the request inline if POLLFREE is seen. However, that solution had two bugs. First, it introduced a deadlock, as it unconditionally locked the aio context while holding the waitqueue lock, which inverts the normal locking order. Second, it didn't consider that POLLFREE notifications are missed while the request has been temporarily de-queued. The second problem was solved by my previous patch. This patch then properly fixes the use-after-free by handling POLLFREE in a deadlock-free way. It does this by taking advantage of the fact that freeing of the waitqueue is RCU-delayed, similar to what eventpoll does.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from [email protected]

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

Problem Types: CWE-416

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 2c14fa838cbefc23cf1c73ca167ed85b274b2913 321fba81ec034f88aea4898993c1bf15605c023f git Not specified
CNA Linux Linux affected 2c14fa838cbefc23cf1c73ca167ed85b274b2913 4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f git Not specified
CNA Linux Linux affected 2c14fa838cbefc23cf1c73ca167ed85b274b2913 47ffefd88abfffe8a040bcc1dd0554d4ea6f7689 git Not specified
CNA Linux Linux affected 2c14fa838cbefc23cf1c73ca167ed85b274b2913 60d311f9e6381d779d7d53371f87285698ecee24 git Not specified
CNA Linux Linux affected 2c14fa838cbefc23cf1c73ca167ed85b274b2913 50252e4b5e989ce64555c7aef7516bdefc2fea72 git Not specified
CNA Linux Linux affected 4.18 Not specified
CNA Linux Linux unaffected 4.18 semver Not specified
CNA Linux Linux unaffected 4.19.221 4.19.* semver Not specified
CNA Linux Linux unaffected 5.4.165 5.4.* semver Not specified
CNA Linux Linux unaffected 5.10.85 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.8 5.15.* semver Not specified
CNA Linux Linux unaffected 5.16 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/321fba81ec034f88aea4898993c1bf15605c023f af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/47ffefd88abfffe8a040bcc1dd0554d4ea6f7689 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/50252e4b5e989ce64555c7aef7516bdefc2fea72 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/60d311f9e6381d779d7d53371f87285698ecee24 af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
git.kernel.org/stable/c/4105e6a128e8a98455dfc9e6dbb2ab0c33c4497f af854a3a-2127-422b-91ae-364da2661108 git.kernel.org Patch
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

© CVE.report 2026

Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties, implied or otherwise, with regard to this information or its use. Any use of this information is at the user's risk. It is the responsibility of user to evaluate the accuracy, completeness or usefulness of any information, opinion, advice or other content. EACH USER WILL BE SOLELY RESPONSIBLE FOR ANY consequences of his or her direct or indirect use of this web site. ALL WARRANTIES OF ANY KIND ARE EXPRESSLY DISCLAIMED. This site will NOT BE LIABLE FOR ANY DIRECT, INDIRECT or any other kind of loss.

CVE, CWE, and OVAL are registred trademarks of The MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. This site includes MITRE data granted under the following license.

Free CVE JSON API cve.report/api

CVE.report and Source URL Uptime Status status.cve.report