[PATCH 5.4 01/34] Bluetooth: L2CAP: Fix use-after-free caused by l2cap_chan_put

Greg Kroah-Hartman
2022-08-01T11:48:09Z

From: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

commit d0be8347c623e0ac4202a1d4e0373882821f56b0 upstream.

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@kernel.org
Reported-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Tested-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/bluetooth/l2cap.h | 1
net/bluetooth/l2cap_core.c | 61 +++++++++++++++++++++++++++++++++---------
2 files changed, 49 insertions(+), 13 deletions(-)

--- a/include/net/bluetooth/l2cap.h
+++ b/include/net/bluetooth/l2cap.h
@@ -802,6 +802,7 @@ 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)
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -110,7 +110,8 @@ static struct l2cap_chan *__l2cap_get_ch
}

/* 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)
{
@@ -118,15 +119,19 @@ static struct l2cap_chan *l2cap_get_chan

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)
@@ -135,8 +140,12 @@ static struct l2cap_chan *l2cap_get_chan

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;
@@ -161,8 +170,12 @@ static struct l2cap_chan *l2cap_get_chan

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;
@@ -496,6 +509,16 @@ void l2cap_chan_hold(struct l2cap_chan *
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 %d", c, kref_read(&c->kref));
@@ -1812,7 +1835,10 @@ static struct l2cap_chan *l2cap_global_c
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;
}
@@ -1827,7 +1853,7 @@ static struct l2cap_chan *l2cap_global_c
}

if (c1)
- l2cap_chan_hold(c1);
+ c1 = l2cap_chan_hold_unless_zero(c1);

read_unlock(&chan_list_lock);

@@ -4221,6 +4247,7 @@ static inline int l2cap_config_req(struc

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

@@ -4334,6 +4361,7 @@ static inline int l2cap_config_rsp(struc

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

@@ -5062,6 +5090,7 @@ send_move_response:
l2cap_send_move_chan_rsp(chan, result);

l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);

return 0;
}
@@ -5154,6 +5183,7 @@ static void l2cap_move_continue(struct l
}

l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);
}

static void l2cap_move_fail(struct l2cap_conn *conn, u8 ident, u16 icid,
@@ -5183,6 +5213,7 @@ static void l2cap_move_fail(struct l2cap
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,
@@ -5246,6 +5277,7 @@ static int l2cap_move_channel_confirm(st
l2cap_send_move_chan_cfm_rsp(conn, cmd->ident, icid);

l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);

return 0;
}
@@ -5281,6 +5313,7 @@ static inline int l2cap_move_channel_con
}

l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);

return 0;
}
@@ -5653,12 +5686,11 @@ static inline int l2cap_le_credits(struc
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;
@@ -5669,7 +5701,9 @@ static inline int l2cap_le_credits(struc
if (chan->tx_credits)
chan->ops->resume(chan);

+unlock:
l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);

return 0;
}
@@ -6983,6 +7017,7 @@ drop:

done:
l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);
}

static void l2cap_conless_channel(struct l2cap_conn *conn, __le16 psm,
@@ -7386,7 +7421,7 @@ static struct l2cap_chan *l2cap_global_f
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;
}