[PATCH v4] staging: pi433: fix race condition in pi433_ioctl

From: Hugo Lefeuvre
Date: Wed Jun 13 2018 - 21:04:52 EST

In the PI433_IOC_WR_TX_CFG case in pi433_ioctl, instance->tx_cfg is
modified via

copy_from_user(&instance->tx_cfg, argp, sizeof(struct pi433_tx_cfg)))

without any kind of synchronization. In the case where two threads
would execute this same command concurrently the tx_cfg field might
enter in an inconsistent state.

Additionally: if ioctl(PI433_IOC_WR_TX_CFG) and write() execute
concurrently the tx config might be modified while it is being
copied to the fifo, resulting in potential data corruption.

Fix: Get instance->tx_cfg_lock before modifying tx config in the
PI433_IOC_WR_TX_CFG case in pi433_ioctl.

Also, do not copy data directly from user space to instance->tx_cfg.
Instead use a temporary buffer allowing future checks for correctness
of copied data and simpler code.

Signed-off-by: Hugo Lefeuvre <hle@xxxxxxxxxx>
Changes in v4:
- Fix incorrect buffer name in memcpy.
drivers/staging/pi433/pi433_if.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/pi433/pi433_if.c b/drivers/staging/pi433/pi433_if.c
index b061f77dda41..94e0bfcec991 100644
--- a/drivers/staging/pi433/pi433_if.c
+++ b/drivers/staging/pi433/pi433_if.c
@@ -880,6 +880,7 @@ pi433_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
int retval = 0;
struct pi433_instance *instance;
struct pi433_device *device;
+ struct pi433_tx_cfg tx_cfg;
void __user *argp = (void __user *)arg;

/* Check type and command number */
@@ -902,9 +903,11 @@ pi433_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
return -EFAULT;
case PI433_IOC_WR_TX_CFG:
- if (copy_from_user(&instance->tx_cfg, argp,
- sizeof(struct pi433_tx_cfg)))
+ if (copy_from_user(&tx_cfg, argp, sizeof(struct pi433_tx_cfg)))
return -EFAULT;
+ mutex_lock(&device->tx_fifo_lock);
+ memcpy(&instance->tx_cfg, &tx_cfg, sizeof(struct pi433_tx_cfg));
+ mutex_unlock(&device->tx_fifo_lock);
case PI433_IOC_RD_RX_CFG:
if (copy_to_user(argp, &device->rx_cfg,

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