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[104.199.160.21]) by smtp.gmail.com with UTF8SMTPSA id z6-20020a170902708600b001a04d27ee92sm2077752plk.241.2023.05.31.19.38.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 31 May 2023 19:38:48 -0700 (PDT) From: Ying Hsu To: linux-bluetooth@vger.kernel.org Cc: chromeos-bluetooth-upstreaming@chromium.org, Ying Hsu , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Johan Hedberg , Luiz Augusto von Dentz , Marcel Holtmann , Min Li , Paolo Abeni , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH v6] Bluetooth: Fix l2cap_disconnect_req deadlock Date: Thu, 1 Jun 2023 02:38:32 +0000 Message-ID: <20230601023835.1117866-1-yinghsu@chromium.org> X-Mailer: git-send-email 2.41.0.rc0.172.g3f132b7071-goog MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-bluetooth@vger.kernel.org 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 releases chan->lock before acquiring the conn_chan_lock to avoid the potential deadlock. Fixes: a2a9339e1c9d ("Bluetooth: L2CAP: Fix use-after-free in l2cap_disconnect_{req,rsp}") Signed-off-by: Ying Hsu --- This commit has been tested on a Chromebook device. Changes in v6: - Fixing format of the fixes tag. Changes in v5: - Fixing the merge conflict by removing l2cap_del_chan_by_scid. Changes in v4: - Using l2cap_get_chan_by_scid to avoid repeated code. - Releasing chan->lock before acquiring conn->chan_lock. Changes in v3: - Adding the fixes tag. Changes in v2: - Adding the prefix "Bluetooth:" to subject line. net/bluetooth/l2cap_core.c | 37 +++++++++++++++---------------------- 1 file changed, 15 insertions(+), 22 deletions(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 036bc147f4de..16ac4aac0638 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -4634,26 +4634,6 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn, return err; } -static struct l2cap_chan *l2cap_del_chan_by_scid(struct l2cap_conn *conn, - u16 cid, int err) -{ - struct l2cap_chan *c; - - mutex_lock(&conn->chan_lock); - c = __l2cap_get_chan_by_scid(conn, cid); - if (c) { - /* Only lock if chan reference is not 0 */ - c = l2cap_chan_hold_unless_zero(c); - if (c) { - l2cap_chan_lock(c); - l2cap_chan_del(c, err); - } - } - mutex_unlock(&conn->chan_lock); - - return c; -} - static inline int l2cap_disconnect_req(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd, u16 cmd_len, u8 *data) @@ -4671,7 +4651,7 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, BT_DBG("scid 0x%4.4x dcid 0x%4.4x", scid, dcid); - chan = l2cap_del_chan_by_scid(conn, dcid, ECONNRESET); + chan = l2cap_get_chan_by_scid(conn, dcid); if (!chan) { cmd_reject_invalid_cid(conn, cmd->ident, dcid, scid); return 0; @@ -4682,6 +4662,13 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, l2cap_send_cmd(conn, cmd->ident, L2CAP_DISCONN_RSP, sizeof(rsp), &rsp); chan->ops->set_shutdown(chan); + + l2cap_chan_unlock(chan); + mutex_lock(&conn->chan_lock); + l2cap_chan_lock(chan); + l2cap_chan_del(chan, ECONNRESET); + mutex_unlock(&conn->chan_lock); + chan->ops->close(chan); l2cap_chan_unlock(chan); @@ -4706,7 +4693,7 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn, BT_DBG("dcid 0x%4.4x scid 0x%4.4x", dcid, scid); - chan = l2cap_del_chan_by_scid(conn, scid, 0); + chan = l2cap_get_chan_by_scid(conn, scid); if (!chan) return 0; @@ -4716,6 +4703,12 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn, return 0; } + l2cap_chan_unlock(chan); + mutex_lock(&conn->chan_lock); + l2cap_chan_lock(chan); + l2cap_chan_del(chan, 0); + mutex_unlock(&conn->chan_lock); + chan->ops->close(chan); l2cap_chan_unlock(chan);