[PATCH net v4] mac802154: fix data race and NULL deref on local->assoc_dev

[PATCH net v4] 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 recorded result is exposed to the same window. assoc_status and
assoc_addr are written by the handler but read by the association path
while the associating bit is still set, so a second response for the same
request - a malicious one, for instance - can replace them between those
reads and leave the caller with an incoherent status and address pair.

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.

wpan_dev->association_lock cannot be reused here: nl802154_associate()
holds it across rdev_associate(), hence for the whole of
mac802154_perform_association() including the wait for the response.
A response handler taking that lock would only get it once the
association has already given up.

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

The handler clears the bit before completing, not the woken waiter:
otherwise complete() is issued under the lock and a second (e.g.
malicious) response can reacquire it before the waiter and replace the
result. So a wait that returns success implies the bit is already clear,
and the success and negative-response paths return directly. The
transmit-error and timeout paths still clear it under assoc_lock, which
serializes any racing response against the cleanup while the call returns
the error it already selected. Both paths snapshot assoc_status and
assoc_addr under the same lock.

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@bootlin.com>
Suggested-by: Xuanqiang Luo <xuanqiang.luo@linux.dev>
Fixes: fefd19807fe9 ("mac802154: Handle associating")
Cc: stable@vger.kernel.org
Signed-off-by: Kaiwen Shi <skwkevin@mail.ustc.edu.cn>
---

v4:
 - move clear_bit(IEEE802154_IS_ASSOCIATING) out of
   mac802154_perform_association() and into
   mac802154_process_association_resp(), after the first valid response
   is saved and before complete(). Clearing it only once the waiter is
   woken still leaves a window: complete() is issued under assoc_lock,
   and before the waiter reacquires that lock another response can pass
   the in-lock recheck and replace the result (Xuanqiang);
 - say in the commit message why wpan_dev->association_lock cannot be
   reused for this;
 - complete the assoc_lock comment.

v3:
 - clear IEEE802154_IS_ASSOCIATING and snapshot assoc_status/assoc_addr
   under assoc_lock right after wait_for_completion returns, so a second
   (e.g. malicious) response can no longer pass the recheck and overwrite
   them while perform_association() consumes the result (Miquel).

v2:
 - replace assoc_dev with the cached coordinator extended address, as
   suggested by Miquel;
 - use a plain spinlock instead of spin_lock_bh(), since both users run
   in process context;
 - protect the cached address and the association-state transitions
   with the same lock;
 - recheck the association state in the response handler and signal the
   completion before releasing the lock;
 - add Cc: stable@vger.kernel.org.

Link to v3:
https://lore.kernel.org/r/20260827221339.885245-1-skwkevin@mail.ustc.edu.cn

Link to v2:
https://lore.kernel.org/r/20260826225959.682483-1-skwkevin@mail.ustc.edu.cn

Link to v1:
https://lore.kernel.org/r/20260824175938.11143-1-skwkevin@mail.ustc.edu.cn
 net/mac802154/ieee802154_i.h |  7 ++++-
 net/mac802154/main.c         |  1 +
 net/mac802154/scan.c         | 51 +++++++++++++++++++++++++++---------
 3 files changed, 45 insertions(+), 14 deletions(-)

diff --git a/net/mac802154/ieee802154_i.h b/net/mac802154/ieee802154_i.h
index 8f2bff268392..c53aa293a222 100644
--- a/net/mac802154/ieee802154_i.h
+++ b/net/mac802154/ieee802154_i.h
@@ -76,7 +76,12 @@ struct ieee802154_local {
 	struct work_struct rx_mac_cmd_work;
 
 	/* Association */
-	struct ieee802154_pan_device *assoc_dev;
+	/* assoc_lock protects assoc_dev_extended_addr, assoc_addr,
+	 * assoc_status, the assoc_done reinit/complete pairing and the
+	 * IEEE802154_IS_ASSOCIATING bit in @ongoing.
+	 */
+	spinlock_t assoc_lock;
+	__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..dd156c01ac49 100644
--- a/net/mac802154/scan.c
+++ b/net/mac802154/scan.c
@@ -536,7 +536,9 @@ int mac802154_perform_association(struct ieee802154_sub_if_data *sdata,
 	struct ieee802154_association_req_frame frame = {};
 	struct ieee802154_local *local = sdata->local;
 	struct wpan_dev *wpan_dev = &sdata->wpan_dev;
+	__le16 resp_short_addr;
 	struct sk_buff *skb;
+	u8 resp_status;
 	int ret;
 
 	frame.mhr.fc.type = IEEE802154_FC_TYPE_MAC_CMD;
@@ -578,9 +580,11 @@ 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) {
@@ -599,25 +603,37 @@ int mac802154_perform_association(struct ieee802154_sub_if_data *sdata,
 		goto clear_assoc;
 	}
 
-	if (local->assoc_status != IEEE802154_ASSOCIATION_SUCCESSFUL) {
-		if (local->assoc_status == IEEE802154_PAN_AT_CAPACITY)
+	/* The association is complete: mac802154_process_association_resp()
+	 * cleared the associating bit before waking us, so a second (e.g.
+	 * malicious) ASSOC RESP can no longer pass the recheck and overwrite
+	 * the result.  Snapshot assoc_status/assoc_addr under the lock.
+	 */
+	spin_lock(&local->assoc_lock);
+	resp_status = local->assoc_status;
+	resp_short_addr = local->assoc_addr;
+	spin_unlock(&local->assoc_lock);
+
+	if (resp_status != IEEE802154_ASSOCIATION_SUCCESSFUL) {
+		if (resp_status == IEEE802154_PAN_AT_CAPACITY)
 			ret = -ERANGE;
 		else
 			ret = -EPERM;
 
 		dev_warn(&sdata->dev->dev,
 			 "Negative ASSOC RESP received from %8phC: %s\n", &ceaddr,
-			 local->assoc_status == IEEE802154_PAN_AT_CAPACITY ?
+			 resp_status == IEEE802154_PAN_AT_CAPACITY ?
 			 "PAN at capacity" : "access denied");
-		goto clear_assoc;
+		return ret;
 	}
 
-	ret = 0;
-	*short_addr = local->assoc_addr;
+	*short_addr = resp_short_addr;
+
+	return 0;
 
 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 +655,28 @@ 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;
+	/* Clear the associating bit before waking the waiter: once the result
+	 * is saved, any subsequent (e.g. malicious) ASSOC RESP must fail the
+	 * test_bit() recheck above and can no longer overwrite the result.
+	 */
+	clear_bit(IEEE802154_IS_ASSOCIATING, &local->ongoing);
+	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

Re: [PATCH net v4] mac802154: fix data race and NULL deref on local->assoc_dev

[luoxuanqiang]

在 2026/8/30 07:05, Kaiwen Shi 写道:
> 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 recorded result is exposed to the same window. assoc_status and
> assoc_addr are written by the handler but read by the association path
> while the associating bit is still set, so a second response for the same
> request - a malicious one, for instance - can replace them between those
> reads and leave the caller with an incoherent status and address pair.
>
> 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.
>
> wpan_dev->association_lock cannot be reused here: nl802154_associate()
> holds it across rdev_associate(), hence for the whole of
> mac802154_perform_association() including the wait for the response.
> A response handler taking that lock would only get it once the
> association has already given up.
>
> Reset the completion, publish the cached address, and set the associating
> bit while holding the lock. The response handler takes the lock, rechecks
> the bit and the cached address, records the response, clears the bit, and
> only then completes the waiter. Thus cleanup cannot pass the handler
> between its state check and completion, and the cached 64-bit value
> cannot tear.
>
> The handler clears the bit before completing, not the woken waiter:
> otherwise complete() is issued under the lock and a second (e.g.
> malicious) response can reacquire it before the waiter and replace the
> result. So a wait that returns success implies the bit is already clear,
> and the success and negative-response paths return directly. The
> transmit-error and timeout paths still clear it under assoc_lock, which
> serializes any racing response against the cleanup while the call returns
> the error it already selected. Both paths snapshot assoc_status and
> assoc_addr under the same lock.
>
> 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@bootlin.com>
> Suggested-by: Xuanqiang Luo <xuanqiang.luo@linux.dev>

Thanks for the update.

I don't think my review warrants a Suggested-by tag here. I only pointed
out a small issue, which did not alter your original approach.

Other than that, the current version looks good to me. Please drop my
Suggested-by tag and feel free to add:

Reviewed-by: Xuanqiang Luo <luoxuanqiang@kylinos.cn>

Here are some related discussions about when a Suggested-by tag is
appropriate, for reference:
https://docs.kernel.org/process/submitting-patches.html#using-reported-by-tested-by-reviewed-by-suggested-by-and-fixes
https://lore.kernel.org/netdev/20260803190044.274355ea@kernel.org/
https://lore.kernel.org/netdev/CANn89i+O5b0xfcP5GLtUopqHz2ppewK9zSr4995jsjCPM+3AFQ@mail.gmail.com/
https://lore.kernel.org/netdev/CAAVpQUDaYX5ZQN+EYL3q4yeu0Ni2cqNODEY--Wb-2+yY650Mbw@mail.gmail.com/
https://lore.kernel.org/netdev/20251010065515.GA3115768@horms.kernel.org/

Thanks,
Xuanqiang