From: Lukas Wunner lukas@wunner.de

hi3110_get_berr_counter() may run concurrently to the rest of the driver but neglects to acquire the lock protecting access to the SPI device. As a result, it and the rest of the driver may clobber each other's tx and rx buffers.

We became aware of this issue because transmission of packets with "cangen -g 0 -i -x" frequently hung. It turns out that agetty executes ->do_get_berr_counter every few seconds via the following call stack:

CPU: 2 PID: 1605 Comm: agetty [<7f3f7500>] (hi3110_get_berr_counter [hi311x]) [<7f130204>] (can_fill_info [can_dev]) [<80693bc0>] (rtnl_fill_ifinfo) [<806949ec>] (rtnl_dump_ifinfo) [<806b4834>] (netlink_dump) [<806b4bc8>] (netlink_recvmsg) [<8065f180>] (sock_recvmsg) [<80660f90>] (___sys_recvmsg) [<80661e7c>] (__sys_recvmsg) [<80661ec0>] (SyS_recvmsg) [<80108b20>] (ret_fast_syscall+0x0/0x1c)

agetty listens to netlink messages in order to update the login prompt when IP addresses change (if /etc/issue contains \4 or \6 escape codes): https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/commit/?id=e3...

It's a useful feature, though it seems questionable that it causes CAN bit error statistics to be queried.

Be that as it may, if hi3110_get_berr_counter() is invoked while a frame is sent by hi3110_hw_tx(), bogus SPI transfers like the following may occur:

=> 12 00 (hi3110_get_berr_counter() wanted to transmit EC 00 to query the transmit error counter, but the first byte was overwritten by hi3110_hw_tx_frame())

=> EA 00 3E 80 01 FB (hi3110_hw_tx_frame() wanted to transmit a frame, but the first byte was overwritten by hi3110_get_berr_counter() because it wanted to query the receive error counter)

This sequence hangs the transmission because the driver believes it has sent a frame and waits for the interrupt signaling completion, but in reality the chip has never sent away the frame since the commands it received were malformed.

Fix by acquiring the SPI lock in hi3110_get_berr_counter().

I've scrutinized the entire driver for further unlocked SPI accesses but found no others.

Cc: Mathias Duckeck m.duckeck@kunbus.de Cc: Akshay Bhat akshay.bhat@timesys.com Cc: Casey Fitzpatrick casey.fitzpatrick@timesys.com Cc: Stef Walter stefw@redhat.com Cc: Karel Zak kzak@redhat.com Cc: stable@vger.kernel.org # v4.12+ Signed-off-by: Lukas Wunner lukas@wunner.de Reviewed-by: Akshay Bhat akshay.bhat@timesys.com Signed-off-by: Marc Kleine-Budde mkl@pengutronix.de --- drivers/net/can/spi/hi311x.c | 2 ++ 1 file changed, 2 insertions(+)

diff --git a/drivers/net/can/spi/hi311x.c b/drivers/net/can/spi/hi311x.c index 5590c559a8ca..c2cf254e4e95 100644 --- a/drivers/net/can/spi/hi311x.c +++ b/drivers/net/can/spi/hi311x.c @@ -427,8 +427,10 @@ static int hi3110_get_berr_counter(const struct net_device *net, struct hi3110_priv *priv = netdev_priv(net); struct spi_device *spi = priv->spi;

+ mutex_lock(&priv->hi3110_lock); bec->txerr = hi3110_read(spi, HI3110_READ_TEC); bec->rxerr = hi3110_read(spi, HI3110_READ_REC); + mutex_unlock(&priv->hi3110_lock);

return 0; }