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Message-ID: <20230522143759.2880743-1-yinghsu@chromium.org> Date: Mon, 22 May 2023 14:37:55 +0000 From: Ying Hsu <yinghsu@...omium.org> To: linux-bluetooth@...r.kernel.org Cc: chromeos-bluetooth-upstreaming@...omium.org, Ying Hsu <yinghsu@...omium.org>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Johan Hedberg <johan.hedberg@...il.com>, Luiz Augusto von Dentz <luiz.dentz@...il.com>, Marcel Holtmann <marcel@...tmann.org>, Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org Subject: [PATCH] Fix l2cap_disconnect_req deadlock 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 <yinghsu@...omium.org> --- 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; } -- 2.40.1.698.g37aff9b760-goog
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