can: j1939: transport: j1939_session_tx_dat(): fix use-after-free read in j1939_tp_tx...

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@syzkaller.appspotmail.com
Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Cc: linux-stable <stable@vger.kernel.org> # >= v5.4
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20200807105200.26441-3-o.rempel@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c
index 9f99af5b0b11e74b7718be8fa3300e01fc36a4dc..5bfe6bf15a999242ec3f02540400f3982a7f9a7c 100644 (file)
--- a/net/can/j1939/transport.c
+++ b/net/can/j1939/transport.c
@@ -787,6 +787,18 @@ static int j1939_session_tx_dat(struct j1939_session *session)
                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_txtimer(struct hrtimer *hrtimer)
                 * 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;