GHSA-M8CC-C87R-9QR2
Vulnerability from github – Published: 2025-10-01 09:30 – Updated: 2025-12-12 18:30In the Linux kernel, the following vulnerability has been resolved:
net: phy: transfer phy_config_inband() locking responsibility to phylink
Problem description
Lockdep reports a possible circular locking dependency (AB/BA) between &pl->state_mutex and &phy->lock, as follows.
phylink_resolve() // acquires &pl->state_mutex -> phylink_major_config() -> phy_config_inband() // acquires &pl->phydev->lock
whereas all the other call sites where &pl->state_mutex and &pl->phydev->lock have the locking scheme reversed. Everywhere else, &pl->phydev->lock is acquired at the top level, and &pl->state_mutex at the lower level. A clear example is phylink_bringup_phy().
The outlier is the newly introduced phy_config_inband() and the existing lock order is the correct one. To understand why it cannot be the other way around, it is sufficient to consider phylink_phy_change(), phylink's callback from the PHY device's phy->phy_link_change() virtual method, invoked by the PHY state machine.
phy_link_up() and phy_link_down(), the (indirect) callers of phylink_phy_change(), are called with &phydev->lock acquired. Then phylink_phy_change() acquires its own &pl->state_mutex, to serialize changes made to its pl->phy_state and pl->link_config. So all other instances of &pl->state_mutex and &phydev->lock must be consistent with this order.
Problem impact
I think the kernel runs a serious deadlock risk if an existing phylink_resolve() thread, which results in a phy_config_inband() call, is concurrent with a phy_link_up() or phy_link_down() call, which will deadlock on &pl->state_mutex in phylink_phy_change(). Practically speaking, the impact may be limited by the slow speed of the medium auto-negotiation protocol, which makes it unlikely for the current state to still be unresolved when a new one is detected, but I think the problem is there. Nonetheless, the problem was discovered using lockdep.
Proposed solution
Practically speaking, the phy_config_inband() requirement of having phydev->lock acquired must transfer to the caller (phylink is the only caller). There, it must bubble up until immediately before &pl->state_mutex is acquired, for the cases where that takes place.
Solution details, considerations, notes
This is the phy_config_inband() call graph:
sfp_upstream_ops :: connect_phy()
|
v
phylink_sfp_connect_phy()
|
v
phylink_sfp_config_phy()
|
| sfp_upstream_ops :: module_insert()
| |
| v
| phylink_sfp_module_insert()
| |
| | sfp_upstream_ops :: module_start()
| | |
| | v
| | phylink_sfp_module_start()
| | |
| v v
| phylink_sfp_config_optical()
phylink_start() | | | phylink_resume() v v | | phylink_sfp_set_config() | | | v v v phylink_mac_initial_config() | phylink_resolve() | | phylink_ethtool_ksettings_set() v v v phylink_major_config() | v phy_config_inband()
phylink_major_config() caller #1, phylink_mac_initial_config(), does not acquire &pl->state_mutex nor do its callers. It must acquire &pl->phydev->lock prior to calling phylink_major_config().
phylink_major_config() caller #2, phylink_resolve() acquires &pl->state_mutex, thus also needs to acquire &pl->phydev->lock.
phylink_major_config() caller #3, phylink_ethtool_ksettings_set(), is completely uninteresting, because it only call ---truncated---
{
"affected": [],
"aliases": [
"CVE-2025-39915"
],
"database_specific": {
"cwe_ids": [
"CWE-667"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-10-01T08:15:34Z",
"severity": "MODERATE"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: phy: transfer phy_config_inband() locking responsibility to phylink\n\nProblem description\n===================\n\nLockdep reports a possible circular locking dependency (AB/BA) between\n\u0026pl-\u003estate_mutex and \u0026phy-\u003elock, as follows.\n\nphylink_resolve() // acquires \u0026pl-\u003estate_mutex\n-\u003e phylink_major_config()\n -\u003e phy_config_inband() // acquires \u0026pl-\u003ephydev-\u003elock\n\nwhereas all the other call sites where \u0026pl-\u003estate_mutex and\n\u0026pl-\u003ephydev-\u003elock have the locking scheme reversed. Everywhere else,\n\u0026pl-\u003ephydev-\u003elock is acquired at the top level, and \u0026pl-\u003estate_mutex at\nthe lower level. A clear example is phylink_bringup_phy().\n\nThe outlier is the newly introduced phy_config_inband() and the existing\nlock order is the correct one. To understand why it cannot be the other\nway around, it is sufficient to consider phylink_phy_change(), phylink\u0027s\ncallback from the PHY device\u0027s phy-\u003ephy_link_change() virtual method,\ninvoked by the PHY state machine.\n\nphy_link_up() and phy_link_down(), the (indirect) callers of\nphylink_phy_change(), are called with \u0026phydev-\u003elock acquired.\nThen phylink_phy_change() acquires its own \u0026pl-\u003estate_mutex, to\nserialize changes made to its pl-\u003ephy_state and pl-\u003elink_config.\nSo all other instances of \u0026pl-\u003estate_mutex and \u0026phydev-\u003elock must be\nconsistent with this order.\n\nProblem impact\n==============\n\nI think the kernel runs a serious deadlock risk if an existing\nphylink_resolve() thread, which results in a phy_config_inband() call,\nis concurrent with a phy_link_up() or phy_link_down() call, which will\ndeadlock on \u0026pl-\u003estate_mutex in phylink_phy_change(). Practically\nspeaking, the impact may be limited by the slow speed of the medium\nauto-negotiation protocol, which makes it unlikely for the current state\nto still be unresolved when a new one is detected, but I think the\nproblem is there. Nonetheless, the problem was discovered using lockdep.\n\nProposed solution\n=================\n\nPractically speaking, the phy_config_inband() requirement of having\nphydev-\u003elock acquired must transfer to the caller (phylink is the only\ncaller). There, it must bubble up until immediately before\n\u0026pl-\u003estate_mutex is acquired, for the cases where that takes place.\n\nSolution details, considerations, notes\n=======================================\n\nThis is the phy_config_inband() call graph:\n\n sfp_upstream_ops :: connect_phy()\n |\n v\n phylink_sfp_connect_phy()\n |\n v\n phylink_sfp_config_phy()\n |\n | sfp_upstream_ops :: module_insert()\n | |\n | v\n | phylink_sfp_module_insert()\n | |\n | | sfp_upstream_ops :: module_start()\n | | |\n | | v\n | | phylink_sfp_module_start()\n | | |\n | v v\n | phylink_sfp_config_optical()\n phylink_start() | |\n | phylink_resume() v v\n | | phylink_sfp_set_config()\n | | |\n v v v\n phylink_mac_initial_config()\n | phylink_resolve()\n | | phylink_ethtool_ksettings_set()\n v v v\n phylink_major_config()\n |\n v\n phy_config_inband()\n\nphylink_major_config() caller #1, phylink_mac_initial_config(), does not\nacquire \u0026pl-\u003estate_mutex nor do its callers. It must acquire\n\u0026pl-\u003ephydev-\u003elock prior to calling phylink_major_config().\n\nphylink_major_config() caller #2, phylink_resolve() acquires\n\u0026pl-\u003estate_mutex, thus also needs to acquire \u0026pl-\u003ephydev-\u003elock.\n\nphylink_major_config() caller #3, phylink_ethtool_ksettings_set(), is\ncompletely uninteresting, because it only call\n---truncated---",
"id": "GHSA-m8cc-c87r-9qr2",
"modified": "2025-12-12T18:30:28Z",
"published": "2025-10-01T09:30:25Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-39915"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/052ac41c379c8b87629808be612a482b2d0ae283"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e2a10daba84968f6b5777d150985fd7d6abc9c84"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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