Hi,
On Wed, Jul 6, 2022 at 1:36 PM Luiz Augusto von Dentz
<luiz.dentz@xxxxxxxxx> wrote:
>
> Hi Lee,
>
> On Wed, Jul 6, 2022 at 3:53 AM Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> >
> > On Tue, 05 Jul 2022, Luiz Augusto von Dentz wrote:
> >
> > > Hi Lee,
> > >
> > > On Wed, Jun 29, 2022 at 8:28 AM Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> > > >
> > > > On Tue, 28 Jun 2022, Luiz Augusto von Dentz wrote:
> > > >
> > > > > Hi Eric, Lee,
> > > > >
> > > > > On Mon, Jun 27, 2022 at 4:39 PM Luiz Augusto von Dentz
> > > > > <luiz.dentz@xxxxxxxxx> wrote:
> > > > > >
> > > > > > Hi Eric, Lee,
> > > > > >
> > > > > > On Mon, Jun 27, 2022 at 7:41 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
> > > > > > >
> > > > > > > On Wed, Jun 22, 2022 at 10:27 AM Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> > > > > > > >
> > > > > > > > This change prevents a use-after-free caused by one of the worker
> > > > > > > > threads starting up (see below) *after* the final channel reference
> > > > > > > > has been put() during sock_close() but *before* the references to the
> > > > > > > > channel have been 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
> > > > > > >
> > > > > > > When was the bug added ? (Fixes: tag please)
> > > > > > >
> > > > > > > > Cc: Marcel Holtmann <marcel@xxxxxxxxxxxx>
> > > > > > > > Cc: Johan Hedberg <johan.hedberg@xxxxxxxxx>
> > > > > > > > Cc: Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx>
> > > > > > > > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> > > > > > > > Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> > > > > > > > Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> > > > > > > > Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> > > > > > > > Cc: linux-bluetooth@xxxxxxxxxxxxxxx
> > > > > > > > Cc: netdev@xxxxxxxxxxxxxxx
> > > > > > > > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > > > > > > > ---
> > > > > > > > net/bluetooth/l2cap_core.c | 4 ++--
> > > > > > > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > > > > > > > index ae78490ecd3d4..82279c5919fd8 100644
> > > > > > > > --- a/net/bluetooth/l2cap_core.c
> > > > > > > > +++ b/net/bluetooth/l2cap_core.c
> > > > > > > > @@ -483,9 +483,7 @@ static void l2cap_chan_destroy(struct kref *kref)
> > > > > > > >
> > > > > > > > BT_DBG("chan %p", chan);
> > > > > > > >
> > > > > > > > - write_lock(&chan_list_lock);
> > > > > > > > list_del(&chan->global_l);
> > > > > > > > - write_unlock(&chan_list_lock);
> > > > > > > >
> > > > > > > > kfree(chan);
> > > > > > > > }
> > > > > > > > @@ -501,7 +499,9 @@ void l2cap_chan_put(struct l2cap_chan *c)
> > > > > > > > {
> > > > > > > > BT_DBG("chan %p orig refcnt %u", c, kref_read(&c->kref));
> > > > > > > >
> > > > > > > > + write_lock(&chan_list_lock);
> > > > > > > > kref_put(&c->kref, l2cap_chan_destroy);
> > > > > > > > + write_unlock(&chan_list_lock);
> > > > > > > > }
> > > > > > > > EXPORT_SYMBOL_GPL(l2cap_chan_put);
> > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > > > I do not think this patch is correct.
> > > > > > >
> > > > > > > a kref does not need to be protected by a write lock.
> > > > > > >
> > > > > > > This might shuffle things enough to work around a particular repro you have.
> > > > > > >
> > > > > > > If the patch was correct why not protect kref_get() sides ?
> > > > > > >
> > > > > > > Before the &hdev->rx_work is scheduled (queue_work(hdev->workqueue,
> > > > > > > &hdev->rx_work),
> > > > > > > a reference must be taken.
> > > > > > >
> > > > > > > Then this reference must be released at the end of hci_rx_work() or
> > > > > > > when hdev->workqueue
> > > > > > > is canceled.
> > > > > > >
> > > > > > > This refcount is not needed _if_ the workqueue is properly canceled at
> > > > > > > device dismantle,
> > > > > > > in a synchronous way.
> > > > > > >
> > > > > > > I do not see this hdev->rx_work being canceled, maybe this is the real issue.
> > > > > > >
> > > > > > > There is a call to drain_workqueue() but this is not enough I think,
> > > > > > > because hci_recv_frame()
> > > > > > > can re-arm
> > > > > > > queue_work(hdev->workqueue, &hdev->rx_work);
> > > > > >
> > > > > > I suspect this likely a refcount problem, we do l2cap_get_chan_by_scid:
> > > > > >
> > > > > > /* Find channel with given SCID.
> > > > > > * Returns locked channel. */
> > > > > > static struct l2cap_chan *l2cap_get_chan_by_scid(struct l2cap_conn
> > > > > > *conn, u16 cid)
> > > > > >
> > > > > > So we return a locked channel but that doesn't prevent another thread
> > > > > > to call l2cap_chan_put which doesn't care about l2cap_chan_lock so
> > > > > > perhaps we actually need to host a reference while we have the lock,
> > > > > > at least we do something like that on l2cap_sock.c:
> > > > > >
> > > > > > l2cap_chan_hold(chan);
> > > > > > l2cap_chan_lock(chan);
> > > > > >
> > > > > > __clear_chan_timer(chan);
> > > > > > l2cap_chan_close(chan, ECONNRESET);
> > > > > > l2cap_sock_kill(sk);
> > > > > >
> > > > > > l2cap_chan_unlock(chan);
> > > > > > l2cap_chan_put(chan);
> > > > >
> > > > > Perhaps something like this:
> > > >
> > > > I'm struggling to apply this for test:
> > > >
> > > > "error: corrupt patch at line 6"
> > >
> > > Check with the attached patch.
> >
> > With the patch applied:
> >
> > [ 188.825418][ T75] refcount_t: addition on 0; use-after-free.
> > [ 188.825418][ T75] refcount_t: addition on 0; use-after-free.
>
> Looks like the changes just make the issue more visible since we are
> trying to add a refcount when it is already 0 so this proves the
> design is not quite right since it is removing the object from the
> list only when destroying it while we probably need to do it before.
>
> How about we use kref_get_unless_zero as it appears it was introduced
> exactly for such cases (patch attached.)
Looks like I missed a few places like l2cap_global_chan_by_psm so here
is another version.
> Luiz Augusto von Dentz
--
Luiz Augusto von Dentz
From 235937ac7a39d16e5dabbfca0ac1d58e4cc814d9 Mon Sep 17 00:00:00 2001
From: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
Date: Tue, 28 Jun 2022 15:46:04 -0700
Subject: [PATCH] Bluetooth: L2CAP: WIP
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
---
include/net/bluetooth/l2cap.h | 1 +
net/bluetooth/l2cap_core.c | 58 +++++++++++++++++++++++++++--------
2 files changed, 46 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..3e5d81e971cc 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 +1992,7 @@ 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);
read_unlock(&chan_list_lock);
return c;
}
@@ -1984,7 +2007,7 @@ 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 +4487,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn,
unlock:
l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);
return err;
}
@@ -4578,6 +4602,7 @@ static inline int l2cap_config_rsp(struct l2cap_conn *conn,
done:
l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);
return err;
}
@@ -5305,6 +5330,7 @@ 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 +5423,7 @@ 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 +5453,7 @@ 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 +5517,7 @@ 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 +5553,7 @@ static inline int l2cap_move_channel_confirm_rsp(struct l2cap_conn *conn,
}
l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);
return 0;
}
@@ -5896,12 +5926,11 @@ 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 +5941,9 @@ 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 +7629,7 @@ 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 +8118,7 @@ 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;
}
--
2.35.3
