net: dsa: clean up FDB, MDB, VLAN entries on unbind

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Summary

CVECVE-2025-37864
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-05-09 07:16:07 UTC
Updated2026-06-01 17:16:34 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net: dsa: clean up FDB, MDB, VLAN entries on unbind As explained in many places such as commit b117e1e8a86d ("net: dsa: delete dsa_legacy_fdb_add and dsa_legacy_fdb_del"), DSA is written given the assumption that higher layers have balanced additions/deletions. As such, it only makes sense to be extremely vocal when those assumptions are violated and the driver unbinds with entries still present. But Ido Schimmel points out a very simple situation where that is wrong: https://lore.kernel.org/netdev/ZDazSM5UsPPjQuKr@shredder/ (also briefly discussed by me in the aforementioned commit). Basically, while the bridge bypass operations are not something that DSA explicitly documents, and for the majority of DSA drivers this API simply causes them to go to promiscuous mode, that isn't the case for all drivers. Some have the necessary requirements for bridge bypass operations to do something useful - see dsa_switch_supports_uc_filtering(). Although in tools/testing/selftests/net/forwarding/local_termination.sh, we made an effort to popularize better mechanisms to manage address filters on DSA interfaces from user space - namely macvlan for unicast, and setsockopt(IP_ADD_MEMBERSHIP) - through mtools - for multicast, the fact is that 'bridge fdb add ... self static local' also exists as kernel UAPI, and might be useful to someone, even if only for a quick hack. It seems counter-productive to block that path by implementing shim .ndo_fdb_add and .ndo_fdb_del operations which just return -EOPNOTSUPP in order to prevent the ndo_dflt_fdb_add() and ndo_dflt_fdb_del() from running, although we could do that. Accepting that cleanup is necessary seems to be the only option. Especially since we appear to be coming back at this from a different angle as well. Russell King is noticing that the WARN_ON() triggers even for VLANs: https://lore.kernel.org/netdev/[email protected]/ What happens in the bug report above is that dsa_port_do_vlan_del() fails, then the VLAN entry lingers on, and then we warn on unbind and leak it. This is not a straight revert of the blamed commit, but we now add an informational print to the kernel log (to still have a way to see that bugs exist), and some extra comments gathered from past years' experience, to justify the logic.

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: CWE-617

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 0832cd9f1f023226527e95002d537123061ddac4 5e531e71b9d21d5e985251440e0d722f71299b7a git Not specified
CNA Linux Linux affected 0832cd9f1f023226527e95002d537123061ddac4 86c6613a69bca815f1865ed8cedfd4b9142621ab git Not specified
CNA Linux Linux affected 0832cd9f1f023226527e95002d537123061ddac4 8fcc1e6f808912977caf17366c625b95dc29ba4f git Not specified
CNA Linux Linux affected 0832cd9f1f023226527e95002d537123061ddac4 99c50c98803425378e08a7394dc885506dc85f06 git Not specified
CNA Linux Linux affected 0832cd9f1f023226527e95002d537123061ddac4 7afb5fb42d4950f33af2732b8147c552659f79b7 git Not specified
CNA Linux Linux affected 5.18 Not specified
CNA Linux Linux unaffected 5.18 semver Not specified
CNA Linux Linux unaffected 6.1.175 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.88 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.25 6.12.* semver Not specified
CNA Linux Linux unaffected 6.14.4 6.14.* semver Not specified
CNA Linux Linux unaffected 6.15 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/7afb5fb42d4950f33af2732b8147c552659f79b7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/5e531e71b9d21d5e985251440e0d722f71299b7a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/99c50c98803425378e08a7394dc885506dc85f06 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/86c6613a69bca815f1865ed8cedfd4b9142621ab 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/8fcc1e6f808912977caf17366c625b95dc29ba4f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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