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 d2e914a4a0 ("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: 58256a26bf ("dpll: add reference sync get/set")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Ivan Vecera <ivecera@redhat.com>
Link: https://patch.msgid.link/20260915213047.1352286-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
d798162eb3