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[v3] Bluetooth: Fix l2cap_disconnect_req deadlock

Message ID 20230524110119.602679-1-yinghsu@chromium.org (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series [v3] Bluetooth: Fix l2cap_disconnect_req deadlock | expand

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Context Check Description
netdev/series_format warning Single patches do not need cover letters; Target tree name not specified in the subject
netdev/tree_selection success Guessed tree name to be net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 8 this patch: 8
netdev/cc_maintainers success CCed 4 of 4 maintainers
netdev/build_clang success Errors and warnings before: 8 this patch: 8
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes fail Problems with Fixes tag: 1
netdev/build_allmodconfig_warn success Errors and warnings before: 8 this patch: 8
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 66 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

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 <yinghsu@chromium.org>
---
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(-)
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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;
 }