[v3] Bluetooth: Fix l2cap_disconnect_req deadlock

Commit Message

Ying Hsu May 24, 2023, 11 a.m. UTC

L2CAP assumes that the locks conn->chan_lock and chan->lock are
acquired in the order conn->chan_lock, chan->lock to avoid
potential deadlock.
For example, l2sock_shutdown acquires these locks in the order:
  mutex_lock(&conn->chan_lock)
  l2cap_chan_lock(chan)

However, l2cap_disconnect_req acquires chan->lock in
l2cap_get_chan_by_scid first and then acquires conn->chan_lock
before calling l2cap_chan_del. This means that these locks are
acquired in unexpected order, which leads to potential deadlock:
  l2cap_chan_lock(c)
  mutex_lock(&conn->chan_lock)

This patch uses __l2cap_get_chan_by_scid to replace
l2cap_get_chan_by_scid and adjusts the locking order to avoid the
potential deadlock.

Fixes: ("a2a9339e1c9d Bluetooth: L2CAP: Fix use-after-free in l2cap_disconnect_{req,rsp}")
Signed-off-by: Ying Hsu <[e-mail]>
---
This commit has been tested on a Chromebook device.

Changes in v3:
- Adding the fixes tag.

Changes in v2:
- Adding the prefix "Bluetooth:" to subject line.

 net/bluetooth/l2cap_core.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

Comments

[e-mail] May 24, 2023, 11:33 a.m. UTC | #1

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=750612

---Test result---

Test Summary:
CheckPatch                    PASS      0.70 seconds
GitLint                       PASS      0.31 seconds
SubjectPrefix                 PASS      0.11 seconds
BuildKernel                   PASS      37.20 seconds
CheckAllWarning               PASS      40.25 seconds
CheckSparse                   PASS      45.22 seconds
CheckSmatch                   PASS      125.07 seconds
BuildKernel32                 PASS      35.91 seconds
TestRunnerSetup               PASS      510.24 seconds
TestRunner_l2cap-tester       PASS      19.01 seconds
TestRunner_iso-tester         PASS      25.36 seconds
TestRunner_bnep-tester        PASS      6.56 seconds
TestRunner_mgmt-tester        PASS      127.03 seconds
TestRunner_rfcomm-tester      PASS      9.87 seconds
TestRunner_sco-tester         PASS      9.08 seconds
TestRunner_ioctl-tester       PASS      10.41 seconds
TestRunner_mesh-tester        PASS      7.70 seconds
TestRunner_smp-tester         PASS      8.93 seconds
TestRunner_userchan-tester    PASS      6.59 seconds
IncrementalBuild              PASS      32.29 seconds



---
Regards,
Linux Bluetooth

Patch

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 376b523c7b26..7374e3d046da 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4651,8 +4651,15 @@  static inline int l2cap_disconnect_req(struct l2cap_conn *conn,
 
 	BT_DBG("scid 0x%4.4x dcid 0x%4.4x", scid, dcid);
 
-	chan = l2cap_get_chan_by_scid(conn, dcid);
+	mutex_lock(&conn->chan_lock);
+	chan = __l2cap_get_chan_by_scid(conn, dcid);
+	if (chan) {
+		chan = l2cap_chan_hold_unless_zero(chan);
+		if (chan)
+			l2cap_chan_lock(chan);
+	}
 	if (!chan) {
+		mutex_unlock(&conn->chan_lock);
 		cmd_reject_invalid_cid(conn, cmd->ident, dcid, scid);
 		return 0;
 	}
@@ -4663,14 +4670,13 @@  static inline int l2cap_disconnect_req(struct l2cap_conn *conn,
 
 	chan->ops->set_shutdown(chan);
 
-	mutex_lock(&conn->chan_lock);
 	l2cap_chan_del(chan, ECONNRESET);
-	mutex_unlock(&conn->chan_lock);
 
 	chan->ops->close(chan);
 
 	l2cap_chan_unlock(chan);
 	l2cap_chan_put(chan);
+	mutex_unlock(&conn->chan_lock);
 
 	return 0;
 }
@@ -4691,25 +4697,32 @@  static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn,
 
 	BT_DBG("dcid 0x%4.4x scid 0x%4.4x", dcid, scid);
 
-	chan = l2cap_get_chan_by_scid(conn, scid);
+	mutex_lock(&conn->chan_lock);
+	chan = __l2cap_get_chan_by_scid(conn, scid);
+	if (chan) {
+		chan = l2cap_chan_hold_unless_zero(chan);
+		if (chan)
+			l2cap_chan_lock(chan);
+	}
 	if (!chan) {
+		mutex_unlock(&conn->chan_lock);
 		return 0;
 	}
 
 	if (chan->state != BT_DISCONN) {
 		l2cap_chan_unlock(chan);
 		l2cap_chan_put(chan);
+		mutex_unlock(&conn->chan_lock);
 		return 0;
 	}
 
-	mutex_lock(&conn->chan_lock);
 	l2cap_chan_del(chan, 0);
-	mutex_unlock(&conn->chan_lock);
 
 	chan->ops->close(chan);
 
 	l2cap_chan_unlock(chan);
 	l2cap_chan_put(chan);
+	mutex_unlock(&conn->chan_lock);
 
 	return 0;
 }