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[104.199.160.21]) by smtp.gmail.com with UTF8SMTPSA id d18-20020aa78152000000b0062e0c39977csm4208846pfn.139.2023.05.22.07.38.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 May 2023 07:38:19 -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 , Paolo Abeni , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH] Fix l2cap_disconnect_req deadlock Date: Mon, 22 May 2023 14:37:55 +0000 Message-ID: <20230522143759.2880743-1-yinghsu@chromium.org> X-Mailer: git-send-email 2.40.1.698.g37aff9b760-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 uses __l2cap_get_chan_by_scid to replace l2cap_get_chan_by_scid and adjusts the locking order to avoid the potential deadlock. Signed-off-by: Ying Hsu --- This commit has been tested on a Chromebook device. net/bluetooth/l2cap_core.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 376b523c7b26..8f08192b8fb1 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -4651,8 +4651,16 @@ 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 +4671,13 @@ 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 +4698,32 @@ 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; }