l2tp: pppol2tp: hold reference to session in pppol2tp_ioctl()

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Summary

CVECVE-2026-53262
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-25 09:16:44 UTC
Updated2026-07-08 15:15:55 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: l2tp: pppol2tp: hold reference to session in pppol2tp_ioctl() pppol2tp_ioctl() read sock->sk->sk_user_data directly without any locks or reference counting. If a controllable sleep was induced during copy_from_user() (e.g. via a userfaultfd page fault sleep), a concurrent socket close could trigger pppol2tp_session_close() asynchronously. This frees the l2tp_session structure via the l2tp_session_del_work workqueue. Upon resuming, the ioctl thread dereferences the stale session pointer, resulting in a Use-After-Free (UAF). Fix this by securely fetching the session reference using the RCU-safe, refcounted helper pppol2tp_sock_to_session(sk) on entry. This locks the session's refcount across the sleep. We structured the function to exit via standard err breaks, guaranteeing that l2tp_session_put() is cleanly called on all return paths to drop the reference. To preserve existing behavior we validate the session and its magic signature only for the specific L2TP commands that require it. This ensures that generic/unknown ioctls called on an unconnected socket still return -ENOIOCTLCMD and correctly fall back to generic handlers (e.g. in sock_do_ioctl()).

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.001250000 probability, percentile 0.025510000 (date 2026-07-04)

Problem Types: NVD-CWE-Other

VersionSourceTypeScoreSeverityVector
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 fd558d186df2c13a22455373858bae634a4795af 78cdfdca88cbf731a92f3b9ee5427c633dd94e28 git Not specified
CNA Linux Linux affected fd558d186df2c13a22455373858bae634a4795af e251d4cdfc725c9e7d686161e3b775a0e7d95053 git Not specified
CNA Linux Linux affected fd558d186df2c13a22455373858bae634a4795af 62f327e287cf7b595ae3f73ba72f5cd2a9e9f39f git Not specified
CNA Linux Linux affected fd558d186df2c13a22455373858bae634a4795af a213a8950414c684999dcf03edeea6c46ede172e git Not specified
CNA Linux Linux affected 2.6.35 Not specified
CNA Linux Linux unaffected 2.6.35 semver Not specified
CNA Linux Linux unaffected 6.12.94 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.36 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.13 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/a213a8950414c684999dcf03edeea6c46ede172e 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/e251d4cdfc725c9e7d686161e3b775a0e7d95053 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/78cdfdca88cbf731a92f3b9ee5427c633dd94e28 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/62f327e287cf7b595ae3f73ba72f5cd2a9e9f39f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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