9p: avoid putting oldfid in p9_client_walk() error path

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-63795
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-19 12:16:51 UTC
Updated2026-07-20 15:16:46 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: 9p: avoid putting oldfid in p9_client_walk() error path When p9_client_walk() is called with clone set to false, fid aliases oldfid. If the walk subsequently fails after the request has been sent, the error path jumps to clunk_fid, which currently calls p9_fid_put(fid) unconditionally. This drops a reference to oldfid even though ownership of oldfid remains with the caller. If this is the last reference, oldfid can be clunked and destroyed while the caller still expects it to be valid. A later use or put of oldfid can then trigger a use-after-free or refcount underflow. Fix this by only putting fid in the clunk_fid error path when it does not alias oldfid, matching the existing guard in the error path below. This can be triggered when a multi-component walk is split into multiple p9_client_walk() calls and a later non-cloning walk fails. A reproducer and refcount warning logs are available on request.

Risk And Classification

Primary CVSS: v3.1 10 CRITICAL from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.001730000 probability, percentile 0.069790000 (date 2026-07-20)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary10CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
3.1CNADECLARED10CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected b48dbb998d70b7f48c2ec0a15c3cf47136808e4e 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070 git Not specified
CNA Linux Linux affected b48dbb998d70b7f48c2ec0a15c3cf47136808e4e b84f46179c806450b89821221ea5bd9a1698aba8 git Not specified
CNA Linux Linux affected b48dbb998d70b7f48c2ec0a15c3cf47136808e4e a61bdcba4f64c2f90d01461913f429ab151f1ca6 git Not specified
CNA Linux Linux affected b48dbb998d70b7f48c2ec0a15c3cf47136808e4e 6dbe9443d9f5f7fb6d319a7b77108853ae6c6bea git Not specified
CNA Linux Linux affected b48dbb998d70b7f48c2ec0a15c3cf47136808e4e a7656d368265d085ac9bb85ab31b0cdb72ad8c38 git Not specified
CNA Linux Linux affected b48dbb998d70b7f48c2ec0a15c3cf47136808e4e 1a3860d46e3eb47dbd60339783cdad7904486b9f git Not specified
CNA Linux Linux affected 6.0 Not specified
CNA Linux Linux unaffected 6.0 semver Not specified
CNA Linux Linux unaffected 6.1.177 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.144 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.95 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.38 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.3 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/a61bdcba4f64c2f90d01461913f429ab151f1ca6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/b84f46179c806450b89821221ea5bd9a1698aba8 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6dbe9443d9f5f7fb6d319a7b77108853ae6c6bea 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1a3860d46e3eb47dbd60339783cdad7904486b9f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/99c379ca1e221c3d75c7c804ebbf4e5ee37a3070 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/a7656d368265d085ac9bb85ab31b0cdb72ad8c38 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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