[PATCH net v2 0/2] fix tx buffer concurrent access protection

Fix tx buffer concurrent access protection in isotp_sendmsg().

v2:
 - Change state of struct tpcon to u32 for cmpxchg just support 4-byte
   and 8-byte in some architectures.

Ziyang Xuan (2):
  can: isotp: add result check for wait_event_interruptible()
  can: isotp: fix tx buffer concurrent access in isotp_sendmsg()

 net/can/isotp.c | 48 +++++++++++++++++++++++++++++++++---------------
 1 file changed, 33 insertions(+), 15 deletions(-)

-- 
2.25.1

Using wait_event_interruptible() to wait for complete transmission,
but do not check the result of wait_event_interruptible() which can
be interrupted. It will result in tx buffer has multiple accessers
and the later process interferes with the previous process.

Following is one of the problems reported by syzbot.

=============================================================
WARNING: CPU: 0 PID: 0 at net/can/isotp.c:840 isotp_tx_timer_handler+0x2e0/0x4c0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.13.0-rc7+ #68
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
RIP: 0010:isotp_tx_timer_handler+0x2e0/0x4c0
Call Trace:
 <IRQ>
 ? isotp_setsockopt+0x390/0x390
 __hrtimer_run_queues+0xb8/0x610
 hrtimer_run_softirq+0x91/0xd0
 ? rcu_read_lock_sched_held+0x4d/0x80
 __do_softirq+0xe8/0x553
 irq_exit_rcu+0xf8/0x100
 sysvec_apic_timer_interrupt+0x9e/0xc0
 </IRQ>
 asm_sysvec_apic_timer_interrupt+0x12/0x20

Add result check for wait_event_interruptible() in isotp_sendmsg()
to avoid multiple accessers for tx buffer.

Reported-by: syzbot+78bab6958a614b0c80b9@syzkaller.appspotmail.com
Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Signed-off-by: Ziyang Xuan <redacted>
---
 net/can/isotp.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index caaa532ece94..2ac29c2b2ca6 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c

@@ -865,7 +865,9 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 			return -EAGAIN;
 
 		/* wait for complete transmission of current pdu */
-		wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE);
+		err = wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE);
+		if (err)
+			return err;
 	}
 
 	if (!size || size > MAX_MSG_LENGTH)

-- 
2.25.1

When isotp_sendmsg() concurrent, tx.state of all tx processes can be
ISOTP_IDLE. The conditions so->tx.state != ISOTP_IDLE and
wq_has_sleeper(&so->wait) can not protect tx buffer from being accessed
by multiple tx processes.

We can use cmpxchg() to try to modify tx.state to ISOTP_SENDING firstly.
If the modification of the previous process succeed, the later process
must wait tx.state to ISOTP_IDLE firstly. Thus, we can ensure tx buffer
is accessed by only one process at the same time. And we should also
restore the original tx.state at the subsequent error processes.

Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Signed-off-by: Ziyang Xuan <redacted>
---
 net/can/isotp.c | 46 +++++++++++++++++++++++++++++++---------------
 1 file changed, 31 insertions(+), 15 deletions(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index 2ac29c2b2ca6..d1f54273c0bb 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c

@@ -121,7 +121,7 @@ enum {
 struct tpcon {
 	int idx;
 	int len;
-	u8 state;
+	u32 state;
 	u8 bs;
 	u8 sn;
 	u8 ll_dl;

@@ -848,6 +848,7 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 {
 	struct sock *sk = sock->sk;
 	struct isotp_sock *so = isotp_sk(sk);
+	u32 old_state = so->tx.state;
 	struct sk_buff *skb;
 	struct net_device *dev;
 	struct canfd_frame *cf;

@@ -860,47 +861,55 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 		return -EADDRNOTAVAIL;
 
 	/* we do not support multiple buffers - for now */
-	if (so->tx.state != ISOTP_IDLE || wq_has_sleeper(&so->wait)) {
-		if (msg->msg_flags & MSG_DONTWAIT)
-			return -EAGAIN;
+	if (cmpxchg(&so->tx.state, ISOTP_IDLE, ISOTP_SENDING) != ISOTP_IDLE ||
+	    wq_has_sleeper(&so->wait)) {
+		if (msg->msg_flags & MSG_DONTWAIT) {
+			err = -EAGAIN;
+			goto err_out;
+		}
 
 		/* wait for complete transmission of current pdu */
 		err = wait_event_interruptible(so->wait, so->tx.state == ISOTP_IDLE);
 		if (err)
-			return err;
+			goto err_out;
 	}
 
-	if (!size || size > MAX_MSG_LENGTH)
-		return -EINVAL;
+	if (!size || size > MAX_MSG_LENGTH) {
+		err = -EINVAL;
+		goto err_out;
+	}
 
 	/* take care of a potential SF_DL ESC offset for TX_DL > 8 */
 	off = (so->tx.ll_dl > CAN_MAX_DLEN) ? 1 : 0;
 
 	/* does the given data fit into a single frame for SF_BROADCAST? */
 	if ((so->opt.flags & CAN_ISOTP_SF_BROADCAST) &&
-	    (size > so->tx.ll_dl - SF_PCI_SZ4 - ae - off))
-		return -EINVAL;
+	    (size > so->tx.ll_dl - SF_PCI_SZ4 - ae - off)) {
+		err = -EINVAL;
+		goto err_out;
+	}
 
 	err = memcpy_from_msg(so->tx.buf, msg, size);
 	if (err < 0)
-		return err;
+		goto err_out;
 
 	dev = dev_get_by_index(sock_net(sk), so->ifindex);
-	if (!dev)
-		return -ENXIO;
+	if (!dev) {
+		err = -ENXIO;
+		goto err_out;
+	}
 
 	skb = sock_alloc_send_skb(sk, so->ll.mtu + sizeof(struct can_skb_priv),
 				  msg->msg_flags & MSG_DONTWAIT, &err);
 	if (!skb) {
 		dev_put(dev);
-		return err;
+		goto err_out;
 	}
 
 	can_skb_reserve(skb);
 	can_skb_prv(skb)->ifindex = dev->ifindex;
 	can_skb_prv(skb)->skbcnt = 0;
 
-	so->tx.state = ISOTP_SENDING;
 	so->tx.len = size;
 	so->tx.idx = 0;
 

@@ -956,7 +965,7 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	if (err) {
 		pr_notice_once("can-isotp: %s: can_send_ret %pe\n",
 			       __func__, ERR_PTR(err));
-		return err;
+		goto err_out;
 	}
 
 	if (wait_tx_done) {

@@ -965,6 +974,13 @@ static int isotp_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	}
 
 	return size;
+
+err_out:
+	so->tx.state = old_state;
+	if (so->tx.state == ISOTP_IDLE)
+		wake_up_interruptible(&so->wait);
+
+	return err;
 }
 
 static int isotp_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,

-- 
2.25.1

On 09.10.21 09:40, Ziyang Xuan wrote:

Using wait_event_interruptible() to wait for complete transmission,
but do not check the result of wait_event_interruptible() which can
be interrupted. It will result in tx buffer has multiple accessers
and the later process interferes with the previous process.

Following is one of the problems reported by syzbot.

=============================================================
WARNING: CPU: 0 PID: 0 at net/can/isotp.c:840 isotp_tx_timer_handler+0x2e0/0x4c0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.13.0-rc7+ #68
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014
RIP: 0010:isotp_tx_timer_handler+0x2e0/0x4c0
Call Trace:
  <IRQ>
  ? isotp_setsockopt+0x390/0x390
  __hrtimer_run_queues+0xb8/0x610
  hrtimer_run_softirq+0x91/0xd0
  ? rcu_read_lock_sched_held+0x4d/0x80
  __do_softirq+0xe8/0x553
  irq_exit_rcu+0xf8/0x100
  sysvec_apic_timer_interrupt+0x9e/0xc0
  </IRQ>
  asm_sysvec_apic_timer_interrupt+0x12/0x20

Add result check for wait_event_interruptible() in isotp_sendmsg()
to avoid multiple accessers for tx buffer.

Reported-by: syzbot+78bab6958a614b0c80b9@syzkaller.appspotmail.com
Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Signed-off-by: Ziyang Xuan <redacted>

Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>

Many thanks!
Oliver

On 09.10.21 09:40, Ziyang Xuan wrote:

When isotp_sendmsg() concurrent, tx.state of all tx processes can be
ISOTP_IDLE. The conditions so->tx.state != ISOTP_IDLE and
wq_has_sleeper(&so->wait) can not protect tx buffer from being accessed
by multiple tx processes.

We can use cmpxchg() to try to modify tx.state to ISOTP_SENDING firstly.
If the modification of the previous process succeed, the later process
must wait tx.state to ISOTP_IDLE firstly. Thus, we can ensure tx buffer
is accessed by only one process at the same time. And we should also
restore the original tx.state at the subsequent error processes.

Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Signed-off-by: Ziyang Xuan <redacted>

Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>

Many thanks!
Oliver

On 09.10.2021 15:40:08, Ziyang Xuan wrote:

Fix tx buffer concurrent access protection in isotp_sendmsg().

v2:
 - Change state of struct tpcon to u32 for cmpxchg just support 4-byte
   and 8-byte in some architectures.

Ziyang Xuan (2):
  can: isotp: add result check for wait_event_interruptible()
  can: isotp: fix tx buffer concurrent access in isotp_sendmsg()

Applied to linux-can/testing, added stable on Cc.

Thanks,
Marc

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