[PATCH 5.12 119/178] can: j1939: fix Use-after-Free, hold skb ref while in use

Greg Kroah-Hartman
2021-06-21T16:48:01Z

From: Oleksij Rempel <o.rempel@pengutronix.de>

commit 2030043e616cab40f510299f09b636285e0a3678 upstream.

This patch fixes a Use-after-Free found by the syzbot.

The problem is that a skb is taken from the per-session skb queue,
without incrementing the ref count. This leads to a Use-after-Free if
the skb is taken concurrently from the session queue due to a CTS.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Link: https://lore.kernel.org/r/20210521115720.7533-1-o.rempel@pengutronix.de
Cc: Hillf Danton <hdanton@sina.com>
Cc: linux-stable <stable@vger.kernel.org>
Reported-by: syzbot+220c1a29987a9a490903@syzkaller.appspotmail.com
Reported-by: syzbot+45199c1b73b4013525cf@syzkaller.appspotmail.com
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/can/j1939/transport.c | 54 ++++++++++++++++++++++++++++++++++------------
1 file changed, 40 insertions(+), 14 deletions(-)

--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -330,6 +330,9 @@ static void j1939_session_skb_drop_old(s

if ((do_skcb->offset + do_skb->len) < offset_start) {
__skb_unlink(do_skb, &session->skb_queue);
+ /* drop ref taken in j1939_session_skb_queue() */
+ skb_unref(do_skb);
+
kfree_skb(do_skb);
}
spin_unlock_irqrestore(&session->skb_queue.lock, flags);
@@ -349,12 +352,13 @@ void j1939_session_skb_queue(struct j193

skcb->flags |= J1939_ECU_LOCAL_SRC;

+ skb_get(skb);
skb_queue_tail(&session->skb_queue, skb);
}

static struct
-sk_buff *j1939_session_skb_find_by_offset(struct j1939_session *session,
- unsigned int offset_start)
+sk_buff *j1939_session_skb_get_by_offset(struct j1939_session *session,
+ unsigned int offset_start)
{
struct j1939_priv *priv = session->priv;
struct j1939_sk_buff_cb *do_skcb;
@@ -371,6 +375,10 @@ sk_buff *j1939_session_skb_find_by_offse
skb = do_skb;
}
}
+
+ if (skb)
+ skb_get(skb);
+
spin_unlock_irqrestore(&session->skb_queue.lock, flags);

if (!skb)
@@ -381,12 +389,12 @@ sk_buff *j1939_session_skb_find_by_offse
return skb;
}

-static struct sk_buff *j1939_session_skb_find(struct j1939_session *session)
+static struct sk_buff *j1939_session_skb_get(struct j1939_session *session)
{
unsigned int offset_start;

offset_start = session->pkt.dpo * 7;
- return j1939_session_skb_find_by_offset(session, offset_start);
+ return j1939_session_skb_get_by_offset(session, offset_start);
}

/* see if we are receiver
@@ -776,7 +784,7 @@ static int j1939_session_tx_dat(struct j
int ret = 0;
u8 dat[8];

- se_skb = j1939_session_skb_find_by_offset(session, session->pkt.tx * 7);
+ se_skb = j1939_session_skb_get_by_offset(session, session->pkt.tx * 7);
if (!se_skb)
return -ENOBUFS;

@@ -801,7 +809,8 @@ static int j1939_session_tx_dat(struct j
netdev_err_once(priv->ndev,
"%s: 0x%p: requested data outside of queued buffer: offset %i, len %i, pkt.tx: %i\n",
__func__, session, skcb->offset, se_skb->len , session->pkt.tx);
- return -EOVERFLOW;
+ ret = -EOVERFLOW;
+ goto out_free;
}

if (!len) {
@@ -835,6 +844,12 @@ static int j1939_session_tx_dat(struct j
if (pkt_done)
j1939_tp_set_rxtimeout(session, 250);

+ out_free:
+ if (ret)
+ kfree_skb(se_skb);
+ else
+ consume_skb(se_skb);
+
return ret;
}

@@ -1007,7 +1022,7 @@ static int j1939_xtp_txnext_receiver(str
static int j1939_simple_txnext(struct j1939_session *session)
{
struct j1939_priv *priv = session->priv;
- struct sk_buff *se_skb = j1939_session_skb_find(session);
+ struct sk_buff *se_skb = j1939_session_skb_get(session);
struct sk_buff *skb;
int ret;

@@ -1015,8 +1030,10 @@ static int j1939_simple_txnext(struct j1
return 0;

skb = skb_clone(se_skb, GFP_ATOMIC);
- if (!skb)
- return -ENOMEM;
+ if (!skb) {
+ ret = -ENOMEM;
+ goto out_free;
+ }

can_skb_set_owner(skb, se_skb->sk);

@@ -1024,12 +1041,18 @@ static int j1939_simple_txnext(struct j1

ret = j1939_send_one(priv, skb);
if (ret)
- return ret;
+ goto out_free;

j1939_sk_errqueue(session, J1939_ERRQUEUE_SCHED);
j1939_sk_queue_activate_next(session);

- return 0;
+ out_free:
+ if (ret)
+ kfree_skb(se_skb);
+ else
+ consume_skb(se_skb);
+
+ return ret;
}

static bool j1939_session_deactivate_locked(struct j1939_session *session)
@@ -1170,9 +1193,10 @@ static void j1939_session_completed(stru
struct sk_buff *skb;

if (!session->transmission) {
- skb = j1939_session_skb_find(session);
+ skb = j1939_session_skb_get(session);
/* distribute among j1939 receivers */
j1939_sk_recv(session->priv, skb);
+ consume_skb(skb);
}

j1939_session_deactivate_activate_next(session);
@@ -1744,7 +1768,7 @@ static void j1939_xtp_rx_dat_one(struct
{
struct j1939_priv *priv = session->priv;
struct j1939_sk_buff_cb *skcb;
- struct sk_buff *se_skb;
+ struct sk_buff *se_skb = NULL;
const u8 *dat;
u8 *tpdat;
int offset;
@@ -1786,7 +1810,7 @@ static void j1939_xtp_rx_dat_one(struct
goto out_session_cancel;
}

- se_skb = j1939_session_skb_find_by_offset(session, packet * 7);
+ se_skb = j1939_session_skb_get_by_offset(session, packet * 7);
if (!se_skb) {
netdev_warn(priv->ndev, "%s: 0x%p: no skb found\n", __func__,
session);
@@ -1848,11 +1872,13 @@ static void j1939_xtp_rx_dat_one(struct
j1939_tp_set_rxtimeout(session, 250);
}
session->last_cmd = 0xff;
+ consume_skb(se_skb);
j1939_session_put(session);

return;

out_session_cancel:
+ kfree_skb(se_skb);
j1939_session_timers_cancel(session);
j1939_session_cancel(session, J1939_XTP_ABORT_FAULT);
j1939_session_put(session);