From: Oleksij Rempel o.rempel@pengutronix.de

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 --- net/can/j1939/transport.c | 54 +++++++++++++++++++++++++++++---------- 1 file changed, 40 insertions(+), 14 deletions(-)

diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c index e09d087ba240..c3946c355882 100644 --- a/net/can/j1939/transport.c +++ b/net/can/j1939/transport.c @@ -330,6 +330,9 @@ static void j1939_session_skb_drop_old(struct j1939_session *session)

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 j1939_session *session,

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_offset(struct j1939_session *session, 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_offset(struct j1939_session *session, 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 j1939_session *session) 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 j1939_session *session) 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 j1939_session *session) 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(struct j1939_session *session) 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 j1939_session *session) 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 j1939_session *session)

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(struct j1939_session *session) 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 j1939_session *session, { 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 j1939_session *session, 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_session *session, 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);

base-commit: a4f0377db1254373513b992ff31a351a7111f0fd