Re: [PATCH net] dpll: reject a reference sync pin which is not on the pin's dpll

[Paolo Abeni <pabeni@redhat.com>]

On 9/15/26 23:30, Jakub Kicinski wrote:
> dpll_pin_ref_sync_state_set() resolves the partner's driver private data
> with dpll_pin_on_dpll_priv() and passes the result to ref_sync_get() and
> ref_sync_set() without looking at it. The helper returns NULL when the
> partner holds no ref on that dpll. Of the two drivers implementing the
> feature only zl3073x dereferences the pointer (sync_pin->id); ice ignores
> it, so ice cannot fault here.
> 
> The NULL is a teardown race, not a steady state - zl3073x registers every
> input pin with every channel, so the partner is normally present on the
> dpll the base pin resolves to. zl3073x_dev_stop() unregisters pins one at
> a time, taking and dropping dpll_lock for each, and between the partner's
> turn and the base pin's the partner is out of that dpll's pin_refs while
> still registered with the channels not yet torn down, so
> dpll_pin_available() keeps passing. That path is not only driver removal:
> devlink reload and devlink dev flash both run zl3073x_dev_stop().
> 
> Reproduced by holding that state open with a mock dpll device, which is
> where the frame name comes from:
> 
>   BUG: kernel NULL pointer dereference, address: 0000000000000000
>   Oops: Oops: 0000 [#1] SMP NOPTI
>   RIP: 0010:mock_ref_sync_get+0x5/0x30
>   Call Trace:
>    <TASK>
>    dpll_pin_ref_sync_set+0x19f/0x4a0
>    dpll_nl_pin_set_doit+0x17d/0x840
>    genl_family_rcv_msg_doit+0xd6/0x130
>    genl_rcv_msg+0x181/0x2b0
>    netlink_rcv_skb+0x55/0x100
>    genl_rcv+0x23/0x30
>    netlink_unicast+0x24d/0x370
>    netlink_sendmsg+0x1e2/0x420
>    __sys_sendto+0x1db/0x1f0
>    __x64_sys_sendto+0x1f/0x30
>    do_syscall_64+0xe1/0x490
> 
> Commit d2e914a4a0d0 ("dpll: fix NULL pointer dereference in
> dpll_msg_add_pin_ref_sync()") added the same guard to the read side, which
> the kernel walks into by itself because the delete notification is emitted
> from inside the unregister; the write side needs a pin-set to land in the
> window and was left alone. Test the priv rather than look up pin_refs
> directly, so that the two halves key off the same condition.
> 
> Fixes: 58256a26bfb3 ("dpll: add reference sync get/set")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Note that sashiko suggests more follow-up:

https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260915213047.1352286-1-kuba@kernel.org

/P