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Bluetooth: L2CAP: Fix use-after-free caused by l2cap_chan_put
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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 torvalds#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: [email protected]
Reported-by: Lee Jones <[email protected]>
Signed-off-by: Luiz Augusto von Dentz <[email protected]>
Tested-by: Lee Jones <[email protected]>
Signed-off-by: Luiz Augusto von Dentz <[email protected]>
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@Vudentz
Vudentz committed Jul 26, 2022
1 parent ef61b6e commit d0be834
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Showing 2 changed files with 49 additions and 13 deletions.
1 change: 1 addition & 0 deletions include/net/bluetooth/l2cap.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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)
Expand Down
61 changes: 48 additions & 13 deletions net/bluetooth/l2cap_core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -111,23 +111,28 @@ 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)
{
struct l2cap_chan *c;

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)
Expand All @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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));
Expand Down Expand Up @@ -1968,7 +1991,10 @@ 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;
}
Expand All @@ -1983,7 +2009,7 @@ 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);

Expand Down Expand Up @@ -4463,6 +4489,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn,

unlock:
l2cap_chan_unlock(chan);
l2cap_chan_put(chan);
return err;
}

Expand Down Expand Up @@ -4577,6 +4604,7 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn,

done:
l2cap_chan_unlock(chan);
l2cap_chan_put(chan);
return err;
}

Expand Down Expand Up @@ -5304,6 +5332,7 @@ 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;
}
Expand Down Expand Up @@ -5396,6 +5425,7 @@ 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,
Expand Down Expand Up @@ -5425,6 +5455,7 @@ 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,
Expand Down Expand Up @@ -5488,6 +5519,7 @@ 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;
}
Expand Down Expand Up @@ -5523,6 +5555,7 @@ static inline int l2cap_move_channel_confirm_rsp(struct l2cap_conn *conn,
}

l2cap_chan_unlock(chan);
l2cap_chan_put(chan);

return 0;
}
Expand Down Expand Up @@ -5895,12 +5928,11 @@ 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;
Expand All @@ -5911,7 +5943,9 @@ 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;
}
Expand Down Expand Up @@ -7597,6 +7631,7 @@ 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,
Expand Down Expand Up @@ -8085,7 +8120,7 @@ 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;
}
Expand Down

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