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([110.226.176.248]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29651ccec88sm35062555ad.107.2025.11.06.10.20.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Nov 2025 10:20:30 -0800 (PST) From: ssrane_b23@ee.vjti.ac.in X-Google-Original-From: ssranevjti@gmail.com To: linux-bluetooth@vger.kernel.org Cc: luiz.dentz@gmail.com, marcel@holtmann.org, johan.hedberg@gmail.com, pav@iki.fi, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com, Shaurya Rane Subject: [PATCH v2 1/1] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user Date: Thu, 6 Nov 2025 23:50:16 +0530 Message-Id: <20251106182016.26508-1-ssranevjti@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20251105142251.101852-1-ssranevjti@gmail.com> References: <20251105142251.101852-1-ssranevjti@gmail.com> Precedence: bulk X-Mailing-List: linux-bluetooth@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Shaurya Rane After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to conn->users and conn->hchan. However, l2cap_register_user() and l2cap_unregister_user() still use hci_dev_lock(), creating a race condition where these functions can access conn->users and conn->hchan concurrently with l2cap_conn_del(). This can lead to use-after-free and list corruption bugs, as reported by syzbot. Fix this by changing l2cap_register_user() and l2cap_unregister_user() to use conn->lock instead of hci_dev_lock(), ensuring consistent locking for the l2cap_conn structure. Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del") Changes in v2: - Replaced hci_dev_lock()/unlock() with mutex_lock()/unlock(&conn->lock) in both l2cap_register_user() and l2cap_unregister_user(). - Updated comments to match current locking rules. - Removed unnecessary hci_dev_hold()/hci_dev_put() usage. Signed-off-by: Shaurya Rane --- net/bluetooth/l2cap_core.c | 20 ++++++++------------ 1 file changed, 8 insertions(+), 12 deletions(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index d08320380ad6..29e78801c507 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -1685,17 +1685,15 @@ static void l2cap_info_timeout(struct work_struct *work) int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user) { - struct hci_dev *hdev = conn->hcon->hdev; int ret; /* We need to check whether l2cap_conn is registered. If it is not, we - * must not register the l2cap_user. l2cap_conn_del() is unregisters - * l2cap_conn objects, but doesn't provide its own locking. Instead, it - * relies on the parent hci_conn object to be locked. This itself relies - * on the hci_dev object to be locked. So we must lock the hci device - * here, too. */ + * must not register the l2cap_user. l2cap_conn_del() unregisters + * l2cap_conn objects under conn->lock, and we use the same lock here + * to protect access to conn->users and conn->hchan. + */ - hci_dev_lock(hdev); + mutex_lock(&conn->lock); if (!list_empty(&user->list)) { ret = -EINVAL; @@ -1716,16 +1714,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user) ret = 0; out_unlock: - hci_dev_unlock(hdev); + mutex_unlock(&conn->lock); return ret; } EXPORT_SYMBOL(l2cap_register_user); void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user) { - struct hci_dev *hdev = conn->hcon->hdev; - - hci_dev_lock(hdev); + mutex_lock(&conn->lock); if (list_empty(&user->list)) goto out_unlock; @@ -1734,7 +1730,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user) user->remove(conn, user); out_unlock: - hci_dev_unlock(hdev); + mutex_unlock(&conn->lock); } EXPORT_SYMBOL(l2cap_unregister_user); -- 2.34.1