Data read from a DbC device may be corrupted due to a race between ongoing write and write request completion handler both queuing new transfer blocks (TRBs) if there are remining data in the kfifo.

TRBs may be in incorrct order compared to the data in the kfifo.

Driver fails to keep lock between reading data from kfifo into a dbc request buffer, and queuing the request to the transfer ring.

This allows completed request to re-queue itself in the middle of an ongoing transfer loop, forcing itself between a kfifo read and request TRB write of another request

cpu0 cpu1 (re-queue completed req2)

lock(port_lock) dbc_start_tx() kfifo_out(fifo, req1->buffer) unlock(port_lock) lock(port_lock) dbc_write_complete(req2) dbc_start_tx() kfifo_out(fifo, req2->buffer) unlock(port_lock) lock(port_lock) req2->trb = ring->enqueue; ring->enqueue++ unlock(port_lock) lock(port_lock) req1->trb = ring->enqueue; ring->enqueue++ unlock(port_lock)

In the above scenario a kfifo containing "12345678" would read "1234" to req1 and "5678" to req2, but req2 is queued before req1 leading to data being transmitted as "56781234"

Solve this by adding a flag that prevents starting a new tx if we are already mid dbc_start_tx() during the unlocked part.

The already running dbc_do_start_tx() will make sure the newly completed request gets re-queued as it is added to the request write_pool while holding the lock.

Cc: stable@vger.kernel.org Fixes: dfba2174dc42 ("usb: xhci: Add DbC support in xHCI driver") Tested-by: Łukasz Bartosik ukaszb@chromium.org Signed-off-by: Mathias Nyman mathias.nyman@linux.intel.com --- drivers/usb/host/xhci-dbgcap.h | 1 + drivers/usb/host/xhci-dbgtty.c | 17 ++++++++++++++++- 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci-dbgcap.h b/drivers/usb/host/xhci-dbgcap.h index 47ac72c2286d..5426c971d2d3 100644 --- a/drivers/usb/host/xhci-dbgcap.h +++ b/drivers/usb/host/xhci-dbgcap.h @@ -114,6 +114,7 @@ struct dbc_port { unsigned int tx_boundary;

bool registered; + bool tx_running; };

struct dbc_driver { diff --git a/drivers/usb/host/xhci-dbgtty.c b/drivers/usb/host/xhci-dbgtty.c index d894081d8d15..b7f95565524d 100644 --- a/drivers/usb/host/xhci-dbgtty.c +++ b/drivers/usb/host/xhci-dbgtty.c @@ -47,7 +47,7 @@ dbc_kfifo_to_req(struct dbc_port *port, char *packet) return len; }

-static int dbc_start_tx(struct dbc_port *port) +static int dbc_do_start_tx(struct dbc_port *port) __releases(&port->port_lock) __acquires(&port->port_lock) { @@ -57,6 +57,8 @@ static int dbc_start_tx(struct dbc_port *port) bool do_tty_wake = false; struct list_head *pool = &port->write_pool;

+ port->tx_running = true; + while (!list_empty(pool)) { req = list_entry(pool->next, struct dbc_request, list_pool); len = dbc_kfifo_to_req(port, req->buf); @@ -77,12 +79,25 @@ static int dbc_start_tx(struct dbc_port *port) } }

+ port->tx_running = false; + if (do_tty_wake && port->port.tty) tty_wakeup(port->port.tty);

return status; }

+/* must be called with port->port_lock held */ +static int dbc_start_tx(struct dbc_port *port) +{ + lockdep_assert_held(&port->port_lock); + + if (port->tx_running) + return -EBUSY; + + return dbc_do_start_tx(port); +} + static void dbc_start_rx(struct dbc_port *port) __releases(&port->port_lock) __acquires(&port->port_lock)