[PATCH 5.17 0676/1126] can: isotp: support MSG_TRUNC flag when reading from socket

Greg Kroah-Hartman
2022-04-05T08:36:22Z

From: Oliver Hartkopp <socketcan@hartkopp.net>

[ Upstream commit 42bf50a1795a1854d48717b7361dbdbce496b16b ]

When providing the MSG_TRUNC flag via recvmsg() syscall the return value
provides the real length of the packet or datagram, even when it was longer
than the passed buffer.

Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Link: https://github.com/linux-can/can-utils/issues/347#issuecomment-1065932671
Link: https://lore.kernel.org/all/20220316164258.54155-3-socketcan@hartkopp.net
Suggested-by: Derek Will <derekrobertwill@gmail.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/can/isotp.c | 27 +++++++++++++++------------
1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/net/can/isotp.c b/net/can/isotp.c
index 8966f06e0660..ad61342d2e16 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -1006,29 +1006,28 @@ static int isotp_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
struct sock *sk = sock->sk;
struct sk_buff *skb;
struct isotp_sock *so = isotp_sk(sk);
- int err = 0;
- int noblock;
+ int noblock = flags & MSG_DONTWAIT;
+ int ret = 0;

- noblock = flags & MSG_DONTWAIT;
- flags &= ~MSG_DONTWAIT;
+ if (flags & ~(MSG_DONTWAIT | MSG_TRUNC))
+ return -EINVAL;

if (!so->bound)
return -EADDRNOTAVAIL;

- skb = skb_recv_datagram(sk, flags, noblock, &err);
+ flags &= ~MSG_DONTWAIT;
+ skb = skb_recv_datagram(sk, flags, noblock, &ret);
if (!skb)
- return err;
+ return ret;

if (size < skb->len)
msg->msg_flags |= MSG_TRUNC;
else
size = skb->len;

- err = memcpy_to_msg(msg, skb->data, size);
- if (err < 0) {
- skb_free_datagram(sk, skb);
- return err;
- }
+ ret = memcpy_to_msg(msg, skb->data, size);
+ if (ret < 0)
+ goto out_err;

sock_recv_timestamp(msg, sk, skb);

@@ -1038,9 +1037,13 @@ static int isotp_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
memcpy(msg->msg_name, skb->cb, msg->msg_namelen);
}

+ /* set length of return value */
+ ret = (flags & MSG_TRUNC) ? skb->len : size;
+
+out_err:
skb_free_datagram(sk, skb);

- return size;
+ return ret;
}

static int isotp_release(struct socket *sock)
--
2.34.1