[PATCH 5.8 009/148] can: j1939: transport: j1939_session_tx_dat(): fix use-after-free read in j1939_tp_txtimer()

[Greg Kroah-Hartman]

From: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>

commit cd3b3636c99fcac52c598b64061f3fe4413c6a12 upstream.

The current stack implementation do not support ECTS requests of not
aligned TP sized blocks.

If ECTS will request a block with size and offset spanning two TP
blocks, this will cause memcpy() to read beyond the queued skb (which
does only contain one TP sized block).

Sometimes KASAN will detect this read if the memory region beyond the
skb was previously allocated and freed. In other situations it will stay
undetected. The ETP transfer in any case will be corrupted.

This patch adds a sanity check to avoid this kind of read and abort the
session with error J1939_XTP_ABORT_ECTS_TOO_BIG.

Reported-by: syzbot+5322482fe520b02aea30@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Cc: linux-stable <stable@xxxxxxxxxxxxxxx> # >= v5.4
Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200807105200.26441-3-o.rempel@xxxxxxxxxxxxxx
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/can/j1939/transport.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -787,6 +787,18 @@ static int j1939_session_tx_dat(struct j
 		if (len > 7)
 			len = 7;
 
+		if (offset + len > se_skb->len) {
+			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;
+		}
+
+		if (!len) {
+			ret = -ENOBUFS;
+			break;
+		}
+
 		memcpy(&dat[1], &tpdat[offset], len);
 		ret = j1939_tp_tx_dat(session, dat, len + 1);
 		if (ret < 0) {
@@ -1120,6 +1132,9 @@ static enum hrtimer_restart j1939_tp_txt
 		 * cleanup including propagation of the error to user space.
 		 */
 		break;
+	case -EOVERFLOW:
+		j1939_session_cancel(session, J1939_XTP_ABORT_ECTS_TOO_BIG);
+		break;
 	case 0:
 		session->tx_retry = 0;
 		break;