On Wed, 20 Jul 2022, Luiz Augusto von Dentz wrote:
> From: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
>
> This fixes the following trace which is caused by hci_rx_work starting up
> *after* the final channel reference has been put() during sock_close() but
> *before* the references to the channel have been destroyed, so instead
> the code now rely on kref_get_unless_zero/l2cap_chan_hold_unless_zero to
> prevent referencing a channel that is about to be destroyed.
>
> refcount_t: increment on 0; use-after-free.
> BUG: KASAN: use-after-free in refcount_dec_and_test+0x20/0xd0
> Read of size 4 at addr ffffffc114f5bf18 by task kworker/u17:14/705
>
> CPU: 4 PID: 705 Comm: kworker/u17:14 Tainted: G S W
> 4.14.234-00003-g1fb6d0bd49a4-dirty #28
> Hardware name: Qualcomm Technologies, Inc. SM8150 V2 PM8150
> Google Inc. MSM sm8150 Flame DVT (DT)
> Workqueue: hci0 hci_rx_work
> Call trace:
> dump_backtrace+0x0/0x378
> show_stack+0x20/0x2c
> dump_stack+0x124/0x148
> print_address_description+0x80/0x2e8
> __kasan_report+0x168/0x188
> kasan_report+0x10/0x18
> __asan_load4+0x84/0x8c
> refcount_dec_and_test+0x20/0xd0
> l2cap_chan_put+0x48/0x12c
> l2cap_recv_frame+0x4770/0x6550
> l2cap_recv_acldata+0x44c/0x7a4
> hci_acldata_packet+0x100/0x188
> hci_rx_work+0x178/0x23c
> process_one_work+0x35c/0x95c
> worker_thread+0x4cc/0x960
> kthread+0x1a8/0x1c4
> ret_from_fork+0x10/0x18
>
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
> Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
Signed-off-by isn't the correct tag for this since I wasn't
responsible for any of the coding, nor am I in the merge path.
Either as a v2 or when the patch is applied, please swap out for:
Reported-by: Lee Jones <lee.jones@xxxxxxxxxx>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
Tested-by: Lee Jones <lee.jones@xxxxxxxxxx>
> ---
> include/net/bluetooth/l2cap.h | 1 +
> net/bluetooth/l2cap_core.c | 61 +++++++++++++++++++++++++++--------
> 2 files changed, 49 insertions(+), 13 deletions(-)
>
> diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
> index 3c4f550e5a8b..2f766e3437ce 100644
> --- a/include/net/bluetooth/l2cap.h
> +++ b/include/net/bluetooth/l2cap.h
> @@ -847,6 +847,7 @@ enum {
> };
>
> void l2cap_chan_hold(struct l2cap_chan *c);
> +struct l2cap_chan *l2cap_chan_hold_unless_zero(struct l2cap_chan *c);
> void l2cap_chan_put(struct l2cap_chan *c);
>
> static inline void l2cap_chan_lock(struct l2cap_chan *chan)
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 09ecaf556de5..77c0aac14539 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -111,7 +111,8 @@ static struct l2cap_chan *__l2cap_get_chan_by_scid(struct l2cap_conn *conn,
> }
>
> /* Find channel with given SCID.
> - * Returns locked channel. */
> + * Returns a reference locked channel.
> + */
> static struct l2cap_chan *l2cap_get_chan_by_scid(struct l2cap_conn *conn,
> u16 cid)
> {
> @@ -119,15 +120,19 @@ static struct l2cap_chan *l2cap_get_chan_by_scid(struct l2cap_conn *conn,
>
> mutex_lock(&conn->chan_lock);
> c = __l2cap_get_chan_by_scid(conn, cid);
> - if (c)
> - l2cap_chan_lock(c);
> + if (c) {
> + /* Only lock if chan reference is not 0 */
> + c = l2cap_chan_hold_unless_zero(c);
> + if (c)
> + l2cap_chan_lock(c);
> + }
> mutex_unlock(&conn->chan_lock);
>
> return c;
> }
>
> /* Find channel with given DCID.
> - * Returns locked channel.
> + * Returns a reference locked channel.
> */
> static struct l2cap_chan *l2cap_get_chan_by_dcid(struct l2cap_conn *conn,
> u16 cid)
> @@ -136,8 +141,12 @@ static struct l2cap_chan *l2cap_get_chan_by_dcid(struct l2cap_conn *conn,
>
> mutex_lock(&conn->chan_lock);
> c = __l2cap_get_chan_by_dcid(conn, cid);
> - if (c)
> - l2cap_chan_lock(c);
> + if (c) {
> + /* Only lock if chan reference is not 0 */
> + c = l2cap_chan_hold_unless_zero(c);
> + if (c)
> + l2cap_chan_lock(c);
> + }
> mutex_unlock(&conn->chan_lock);
>
> return c;
> @@ -162,8 +171,12 @@ static struct l2cap_chan *l2cap_get_chan_by_ident(struct l2cap_conn *conn,
>
> mutex_lock(&conn->chan_lock);
> c = __l2cap_get_chan_by_ident(conn, ident);
> - if (c)
> - l2cap_chan_lock(c);
> + if (c) {
> + /* Only lock if chan reference is not 0 */
> + c = l2cap_chan_hold_unless_zero(c);
> + if (c)
> + l2cap_chan_lock(c);
> + }
> mutex_unlock(&conn->chan_lock);
>
> return c;
> @@ -497,6 +510,16 @@ void l2cap_chan_hold(struct l2cap_chan *c)
> kref_get(&c->kref);
> }
>
> +struct l2cap_chan *l2cap_chan_hold_unless_zero(struct l2cap_chan *c)
> +{
> + BT_DBG("chan %p orig refcnt %u", c, kref_read(&c->kref));
> +
> + if (!kref_get_unless_zero(&c->kref))
> + return NULL;
> +
> + return c;
> +}
> +
> void l2cap_chan_put(struct l2cap_chan *c)
> {
> BT_DBG("chan %p orig refcnt %u", c, kref_read(&c->kref));
> @@ -1969,7 +1992,10 @@ static struct l2cap_chan *l2cap_global_chan_by_psm(int state, __le16 psm,
> src_match = !bacmp(&c->src, src);
> dst_match = !bacmp(&c->dst, dst);
> if (src_match && dst_match) {
> - l2cap_chan_hold(c);
> + c = l2cap_chan_hold_unless_zero(c);
> + if (!c)
> + continue;
> +
> read_unlock(&chan_list_lock);
> return c;
> }
> @@ -1984,7 +2010,7 @@ static struct l2cap_chan *l2cap_global_chan_by_psm(int state, __le16 psm,
> }
>
> if (c1)
> - l2cap_chan_hold(c1);
> + c1 = l2cap_chan_hold_unless_zero(c1);
>
> read_unlock(&chan_list_lock);
>
> @@ -4464,6 +4490,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn,
>
> unlock:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> return err;
> }
>
> @@ -4578,6 +4605,7 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn,
>
> done:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> return err;
> }
>
> @@ -5305,6 +5333,7 @@ static inline int l2cap_move_channel_req(struct l2cap_conn *conn,
> l2cap_send_move_chan_rsp(chan, result);
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
>
> return 0;
> }
> @@ -5397,6 +5426,7 @@ static void l2cap_move_continue(struct l2cap_conn *conn, u16 icid, u16 result)
> }
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> }
>
> static void l2cap_move_fail(struct l2cap_conn *conn, u8 ident, u16 icid,
> @@ -5426,6 +5456,7 @@ static void l2cap_move_fail(struct l2cap_conn *conn, u8 ident, u16 icid,
> l2cap_send_move_chan_cfm(chan, L2CAP_MC_UNCONFIRMED);
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> }
>
> static int l2cap_move_channel_rsp(struct l2cap_conn *conn,
> @@ -5489,6 +5520,7 @@ static int l2cap_move_channel_confirm(struct l2cap_conn *conn,
> l2cap_send_move_chan_cfm_rsp(conn, cmd->ident, icid);
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
>
> return 0;
> }
> @@ -5524,6 +5556,7 @@ static inline int l2cap_move_channel_confirm_rsp(struct l2cap_conn *conn,
> }
>
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
>
> return 0;
> }
> @@ -5896,12 +5929,11 @@ static inline int l2cap_le_credits(struct l2cap_conn *conn,
> if (credits > max_credits) {
> BT_ERR("LE credits overflow");
> l2cap_send_disconn_req(chan, ECONNRESET);
> - l2cap_chan_unlock(chan);
>
> /* Return 0 so that we don't trigger an unnecessary
> * command reject packet.
> */
> - return 0;
> + goto unlock;
> }
>
> chan->tx_credits += credits;
> @@ -5912,7 +5944,9 @@ static inline int l2cap_le_credits(struct l2cap_conn *conn,
> if (chan->tx_credits)
> chan->ops->resume(chan);
>
> +unlock:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
>
> return 0;
> }
> @@ -7598,6 +7632,7 @@ static void l2cap_data_channel(struct l2cap_conn *conn, u16 cid,
>
> done:
> l2cap_chan_unlock(chan);
> + l2cap_chan_put(chan);
> }
>
> static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,
> @@ -8086,7 +8121,7 @@ static struct l2cap_chan *l2cap_global_fixed_chan(struct l2cap_chan *c,
> if (src_type != c->src_type)
> continue;
>
> - l2cap_chan_hold(c);
> + c = l2cap_chan_hold_unless_zero(c);
> read_unlock(&chan_list_lock);
> return c;
> }
--
Lee Jones [李琼斯]
Principal Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
Follow Linaro: Facebook | Twitter | Blog
