Re: [PATCH net v2] dpll: fix NULL deref in dpll_device_ops() during teardown race

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 13/08/2026 15:08, Petr Oros wrote:
> When the last owner of a dpll device unregisters while a foreign driver
> still holds a pin on it via dpll_pin_on_pin_register(), the dpll object
> stays alive with an empty registration list. A pin notification queued
> before the unregister (e.g. ice reacting to zl3073x_i2c removal) then
> walks pin->dpll_refs into dpll_device_ops(), which trips the WARN_ON and
> dereferences the missing registration. dpll_lock cannot help because the
> notification work was queued before the unregistering driver took the
> lock.
> 
> Treat the empty registration list as a legitimate transient state. Make
> dpll_priv() and dpll_device_ops() return NULL in that case and make
> every pin netlink path that resolves a device from a pin skip such
> dplls. dpll_cmd_pin_get_one() picks a ref with a live registration and
> returns -ENODEV when there is none, the pin dumpit skips such a pin
> instead of aborting the dump, dpll_msg_add_pin_dplls() and the
> frequency, esync, reference sync and phase adjust set paths skip dead
> refs, and dpll_pin_parent_device_set() validates the parent with
> dpll_device_get_by_id(). dpll_pin_register() is the last caller that
> dereferenced the device ops without a check, so move its frequency
> monitor validation under dpll_lock and tolerate a missing registration
> there as well.
> 
> The empty registration list is equivalent to a cleared DPLL_REGISTERED
> mark, both transitions happen under dpll_lock in dpll_device_register()
> and dpll_device_unregister(). A pin notification for a pin whose dplls
> are all gone is now dropped with -ENODEV instead of crashing, all
> callers in the core ignore that return value.
> 
>   WARNING: drivers/dpll/dpll_core.c:1092 at dpll_device_ops+0x24/0x40,
>   CPU#83: kworker/u576:3/23471
>   Modules linked in: ... ice ... zl3073x_i2c(-) ... zl3073x ...
>   Workqueue: ice_dpll_wq ice_dpll_pin_notify_work [ice]
>   RIP: 0010:dpll_device_ops+0x24/0x40
>   Call Trace:
>    <TASK>
>    dpll_cmd_pin_get_one+0x336/0x520
>    dpll_pin_event_send+0x82/0x140
>    dpll_pin_on_pin_unregister+0xbb/0x160
>    ice_dpll_pin_notify_work+0x1bc/0x1f0 [ice]
>    process_one_work+0x19e/0x370
>    worker_thread+0x1a6/0x310
>    kthread+0xe4/0x120
>    ret_from_fork+0x1a1/0x270
>    ret_from_fork_asm+0x1a/0x30
>    </TASK>
>   ---[ end trace 0000000000000000 ]---
>   BUG: kernel NULL pointer dereference, address: 0000000000000010
>   #PF: supervisor read access in kernel mode
>   #PF: error_code(0x0000) - not-present page
> 
> Fixes: 9431063ad323 ("dpll: core: Add DPLL framework base functions")
> Signed-off-by: Petr Oros <poros@redhat.com>
> ---
> v2:
> - guard every path that resolves a device from a pin, not only the
>    first ref in dpll_cmd_pin_get_one(); skip half-dead refs in
>    dpll_msg_add_pin_dplls() and the set paths, select a live
>    representative ref and turn the pin dumpit -ENODEV into a per pin
>    skip (Jakub)
> - validate the parent device in dpll_pin_parent_device_set() via
>    dpll_device_get_by_id()
> - guard the frequency monitor validation in dpll_pin_register() and
>    perform it under dpll_lock, it was the only remaining unchecked
>    dereference of the device ops
> - drop patch 2/2, superseded by commit 32239d600236 ("dpll: fix stale
>    iteration in dpll_pin_on_pin_unregister()")
> 
> v1: https://lore.kernel.org/all/20260516191317.1005612-2-poros@redhat.com/
> ---
>   drivers/dpll/dpll_core.c    | 24 +++++++++------
>   drivers/dpll/dpll_netlink.c | 59 ++++++++++++++++++++++++++++++++-----
>   2 files changed, 67 insertions(+), 16 deletions(-)
> 

Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>