net/ipv6: release expired exception dst cached in socket

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2024-56644
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2024-12-27 15:15:24 UTC
Updated2026-08-04 11:22:17 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net/ipv6: release expired exception dst cached in socket Dst objects get leaked in ip6_negative_advice() when this function is executed for an expired IPv6 route located in the exception table. There are several conditions that must be fulfilled for the leak to occur: * an ICMPv6 packet indicating a change of the MTU for the path is received, resulting in an exception dst being created * a TCP connection that uses the exception dst for routing packets must start timing out so that TCP begins retransmissions * after the exception dst expires, the FIB6 garbage collector must not run before TCP executes ip6_negative_advice() for the expired exception dst When TCP executes ip6_negative_advice() for an exception dst that has expired and if no other socket holds a reference to the exception dst, the refcount of the exception dst is 2, which corresponds to the increment made by dst_init() and the increment made by the TCP socket for which the connection is timing out. The refcount made by the socket is never released. The refcount of the dst is decremented in sk_dst_reset() but that decrement is counteracted by a dst_hold() intentionally placed just before the sk_dst_reset() in ip6_negative_advice(). After ip6_negative_advice() has finished, there is no other object tied to the dst. The socket lost its reference stored in sk_dst_cache and the dst is no longer in the exception table. The exception dst becomes a leaked object. As a result of this dst leak, an unbalanced refcount is reported for the loopback device of a net namespace being destroyed under kernels that do not contain e5f80fcf869a ("ipv6: give an IPv6 dev to blackhole_netdev"): unregister_netdevice: waiting for lo to become free. Usage count = 2 Fix the dst leak by removing the dst_hold() in ip6_negative_advice(). The patch that introduced the dst_hold() in ip6_negative_advice() was 92f1655aa2b22 ("net: fix __dst_negative_advice() race"). But 92f1655aa2b22 merely refactored the code with regards to the dst refcount so the issue was present even before 92f1655aa2b22. The bug was introduced in 54c1a859efd9f ("ipv6: Don't drop cache route entry unless timer actually expired.") where the expired cached route is deleted and the sk_dst_cache member of the socket is set to NULL by calling dst_negative_advice() but the refcount belonging to the socket is left unbalanced. The IPv4 version - ipv4_negative_advice() - is not affected by this bug. When the TCP connection times out ipv4_negative_advice() merely resets the sk_dst_cache of the socket while decrementing the refcount of the exception dst.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

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

Problem Types: NVD-CWE-Other

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

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

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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 54c1a859efd9fd6cda05bc700315ba2519c14eba a95808252e8acc0123bacd2dff8b9af10bc145b7 git Not specified
CNA Linux Linux affected 54c1a859efd9fd6cda05bc700315ba2519c14eba b90d061345bb8cd51fece561a800bae1c95448a6 git Not specified
CNA Linux Linux affected 54c1a859efd9fd6cda05bc700315ba2519c14eba 0b8903e6c881f72c6849d4952de742c656eb5ab9 git Not specified
CNA Linux Linux affected 54c1a859efd9fd6cda05bc700315ba2519c14eba 535add1e9f274502209cb997801208bbe1ae6c6f git Not specified
CNA Linux Linux affected 54c1a859efd9fd6cda05bc700315ba2519c14eba f43d12fd0fa8ee5b9caf8a3927e10d06431764d2 git Not specified
CNA Linux Linux affected 54c1a859efd9fd6cda05bc700315ba2519c14eba 8b591bd522b71c42a82898290e35d32b482047e4 git Not specified
CNA Linux Linux affected 54c1a859efd9fd6cda05bc700315ba2519c14eba 3301ab7d5aeb0fe270f73a3d4810c9d1b6a9f045 git Not specified
CNA Linux Linux affected 9c93e9c757c7d3d96027a06b9b4c4e37ca87ded7 git Not specified
CNA Linux Linux affected 2.6.33.2 2.6.34 semver Not specified
CNA Linux Linux affected 2.6.34 Not specified
CNA Linux Linux unaffected 2.6.34 semver Not specified
CNA Linux Linux unaffected 5.4.287 5.4.* semver Not specified
CNA Linux Linux unaffected 5.10.231 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.174 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.120 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.66 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.5 6.12.* semver Not specified
CNA Linux Linux unaffected 6.13 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/0b8903e6c881f72c6849d4952de742c656eb5ab9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2025/03/msg00002.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Third Party Advisory
git.kernel.org/stable/c/8b591bd522b71c42a82898290e35d32b482047e4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/3301ab7d5aeb0fe270f73a3d4810c9d1b6a9f045 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/f43d12fd0fa8ee5b9caf8a3927e10d06431764d2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2025/03/msg00001.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Third Party Advisory
git.kernel.org/stable/c/535add1e9f274502209cb997801208bbe1ae6c6f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/a95808252e8acc0123bacd2dff8b9af10bc145b7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/b90d061345bb8cd51fece561a800bae1c95448a6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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