[PATCH net v2] mac802154: fix data race and NULL deref on local->assoc_dev

[Kaiwen Shi]

local->assoc_dev is shared between the association path and the
association-response worker without common synchronization.

mac802154_perform_association() stores the coordinator pointer and waits
for a response. Its timeout and error paths clear the pointer and return
to mac802154_associate(), which may then free the coordinator object.
Meanwhile, mac802154_rx_mac_cmd_worker() may observe the associating bit
and enter mac802154_process_association_resp(), which dereferences
assoc_dev.

The worker's bit test and the handler's pointer dereference are not
atomic with respect to cleanup. Cleanup can clear assoc_dev between them,
causing a NULL dereference, or free the coordinator while the response
handler still uses the pointer.

The response handler only needs the coordinator extended address.
Replace assoc_dev with a cached address, removing the pointer lifetime
dependency. Protect the cached address and the associating bit with a
dedicated spinlock. A READ_ONCE()/WRITE_ONCE() pair would not guarantee
an atomic __le64 access on all 32-bit architectures.

Reset the completion, publish the cached address, and set the associating
bit while holding the lock. Cleanup clears the bit under the same lock.
The response handler takes the lock, rechecks the bit, validates the
cached address, records the response, and completes the waiter before
unlocking. Thus cleanup cannot pass the handler between its state check
and completion, and the cached 64-bit value cannot tear.

Both users run in process context, so a plain spinlock is sufficient.
The lock is not held while waiting for the completion.

Suggested-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
Fixes: fefd19807fe9 ("mac802154: Handle associating")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kaiwen Shi <skwkevin@xxxxxxxxxxxxxxxx>
---
v2:
  - cache the coordinator extended address instead of retaining the
    assoc_dev pointer, as suggested by Miquel;
  - use a plain spinlock to serialize the cached address and associating
    bit, including 64-bit address accesses on 32-bit architectures;
  - reset the completion under the same lock, recheck the associating bit
    in the response handler, and complete before releasing the lock;
  - use the response payload in the debug message;
  - add Cc: stable@xxxxxxxxxxxxxxx.

Link: https://lore.kernel.org/r/20260824175938.11143-1-skwkevin@xxxxxxxxxxxxxxxx

 net/mac802154/ieee802154_i.h |  3 ++-
 net/mac802154/main.c         |  1 +
 net/mac802154/scan.c         | 21 ++++++++++++++-------
 3 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/net/mac802154/ieee802154_i.h b/net/mac802154/ieee802154_i.h
index 8f2bff268392..8f92ac83f5f9 100644
--- a/net/mac802154/ieee802154_i.h
+++ b/net/mac802154/ieee802154_i.h
@@ -76,7 +76,8 @@ struct ieee802154_local {
 	struct work_struct rx_mac_cmd_work;
 
 	/* Association */
-	struct ieee802154_pan_device *assoc_dev;
+	spinlock_t assoc_lock; /* protects association address and active bit */
+	__le64 assoc_dev_extended_addr;
 	struct completion assoc_done;
 	__le16 assoc_addr;
 	u8 assoc_status;
diff --git a/net/mac802154/main.c b/net/mac802154/main.c
index ea1efef3572a..63e89bd586e3 100644
--- a/net/mac802154/main.c
+++ b/net/mac802154/main.c
@@ -104,6 +104,7 @@ ieee802154_alloc_hw(size_t priv_data_len, const struct ieee802154_ops *ops)
 	INIT_WORK(&local->rx_mac_cmd_work, mac802154_rx_mac_cmd_worker);
 
 	init_completion(&local->assoc_done);
+	spin_lock_init(&local->assoc_lock);
 
 	/* init supported flags with 802.15.4 default ranges */
 	phy->supported.max_minbe = 8;
diff --git a/net/mac802154/scan.c b/net/mac802154/scan.c
index 005338f89b75..0ae11e448ccb 100644
--- a/net/mac802154/scan.c
+++ b/net/mac802154/scan.c
@@ -578,9 +578,11 @@ int mac802154_perform_association(struct ieee802154_sub_if_data *sdata,
 		return ret;
 	}
 
-	local->assoc_dev = coord;
+	spin_lock(&local->assoc_lock);
 	reinit_completion(&local->assoc_done);
+	local->assoc_dev_extended_addr = coord->extended_addr;
 	set_bit(IEEE802154_IS_ASSOCIATING, &local->ongoing);
+	spin_unlock(&local->assoc_lock);
 
 	ret = ieee802154_mlme_tx_one_locked(local, sdata, skb);
 	if (ret) {
@@ -616,8 +618,9 @@ int mac802154_perform_association(struct ieee802154_sub_if_data *sdata,
 	*short_addr = local->assoc_addr;
 
 clear_assoc:
+	spin_lock(&local->assoc_lock);
 	clear_bit(IEEE802154_IS_ASSOCIATING, &local->ongoing);
-	local->assoc_dev = NULL;
+	spin_unlock(&local->assoc_lock);
 
 	return ret;
 }
@@ -639,19 +642,23 @@ int mac802154_process_association_resp(struct ieee802154_sub_if_data *sdata,
 		     dest->mode != IEEE802154_EXTENDED_ADDRESSING))
 		return -EINVAL;
 
-	if (unlikely(dest->extended_addr != wpan_dev->extended_addr ||
-		     src->extended_addr != local->assoc_dev->extended_addr))
+	spin_lock(&local->assoc_lock);
+	if (unlikely(!test_bit(IEEE802154_IS_ASSOCIATING, &local->ongoing) ||
+		     dest->extended_addr != wpan_dev->extended_addr ||
+		     src->extended_addr != local->assoc_dev_extended_addr)) {
+		spin_unlock(&local->assoc_lock);
 		return -ENODEV;
+	}
 
 	memcpy(&resp_pl, skb->data, sizeof(resp_pl));
 	local->assoc_addr = resp_pl.short_addr;
 	local->assoc_status = resp_pl.status;
+	complete(&local->assoc_done);
+	spin_unlock(&local->assoc_lock);
 
 	dev_dbg(&skb->dev->dev,
 		"ASSOC RESP 0x%x received from %8phC, getting short address %04x\n",
-		local->assoc_status, &deaddr, local->assoc_addr);
-
-	complete(&local->assoc_done);
+		resp_pl.status, &deaddr, resp_pl.short_addr);
 
 	return 0;
 }

base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
-- 
2.34.1