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Apache NuttX is a mature, real-time embedded operating system (RTOS)
https://nuttx.apache.org/
b82ceb62a7
An unchecked integer assignment in the CAN driver may result in a division-by-zero which would result in a kernel crash (denial of service).
Tested locally, builds fine.
An unchecked integer assignment in the CAN driver may result in a division-by-zero which would result in a kernel crash (denial of service).
The CAN driver `can_ioctl` function, shown below (drivers/can/can.c), receives commands from user processes. Its received arguments `cmd` and content of `arg` are under attacker's control. In the CAN driver, some `ioctl` commands are hardware specific and are processed by calling `dev_ioctl()`. Subsequently, depending on the hardware (STM32 or AT32), this function calls `fdcan_ioctl` or `at32can_ioctl`, as shown in the snippets that follow.
```c
static int can_ioctl(FAR struct file *filep, int cmd, unsigned long arg)
{
FAR struct inode *inode = filep->f_inode;
FAR struct can_dev_s *dev = inode->i_private;
FAR struct can_reader_s *reader = filep->f_priv;
...
flags = enter_critical_section();
/* Handle built-in ioctl commands */
switch (cmd)
{
...
/* Not a "built-in" ioctl command.. perhaps it is unique to this
* lower-half, device driver. */
default:
{
ret = dev_ioctl(dev, cmd, arg);
}
break;
}
leave_critical_section(flags);
return ret;
}
```
There are a few instances where the user can trigger a kernel crash, caused by a division by zero on `CANIOC_SET_BITTIMING` command. On STM32 platforms (arch/arm/src/stm32/stm32_fdcan.c), while there is a `DEBUGASSERT` assertion for `bt->bt_baud`, the check does not cover value `0`.
```c
static const struct can_ops_s g_fdcanops =
{
...
.co_ioctl = fdcan_ioctl,
...
};
static int fdcan_ioctl(struct can_dev_s *dev, int cmd, unsigned long arg)
{
...
switch (cmd)
{
...
case CANIOC_SET_BITTIMING:
{
const struct canioc_bittiming_s *bt = (const struct canioc_bittiming_s *)arg;
uint32_t nbrp;
uint32_t ntseg1;
uint32_t ntseg2;
uint32_t nsjw;
uint32_t ie;
uint8_t state;
DEBUGASSERT(bt != NULL);
DEBUGASSERT(bt->bt_baud < STM32_FDCANCLK_FREQUENCY); // <- not valid
DEBUGASSERT(bt->bt_sjw > 0 && bt->bt_sjw <= 16);
DEBUGASSERT(bt->bt_tseg1 > 1 && bt->bt_tseg1 <= 64);
DEBUGASSERT(bt->bt_tseg2 > 0 && bt->bt_tseg2 <= 16);
/* Extract bit timing data */
ntseg1 = bt->bt_tseg1 - 1;
ntseg2 = bt->bt_tseg2 - 1;
nsjw = bt->bt_sjw - 1;
nbrp = (uint32_t)
( ((float) STM32_FDCANCLK_FREQUENCY /
((float)(ntseg1 + ntseg2 + 3) * (float)bt->bt_baud)) - 1 ); // <- div by 0
```
Similarly, another division by zero was found in Artery Technology AT32 (arch/arm/src/stm32/stm32_can.c) driver:
```c
static const struct can_ops_s g_canops =
{
...
.co_ioctl = at32can_ioctl,
...
};
static int at32can_ioctl(struct can_dev_s *dev, int cmd, unsigned long arg)
{
...
/* Handle the command */
switch (cmd)
{
...
case CANIOC_SET_BITTIMING:
{
const struct canioc_bittiming_s *bt = (const struct canioc_bittiming_s *)arg;
...
uint32_t tmp;
uint32_t regval;
DEBUGASSERT(bt != NULL);
DEBUGASSERT(bt->bt_baud < AT32_PCLK1_FREQUENCY); // <- not valid
DEBUGASSERT(bt->bt_sjw > 0 && bt->bt_sjw <= 4);
DEBUGASSERT(bt->bt_tseg1 > 0 && bt->bt_tseg1 <= 16);
DEBUGASSERT(bt->bt_tseg2 > 0 && bt->bt_tseg2 <= 8);
regval = at32can_getreg(priv, AT32_CAN_BTMG_OFFSET);
/* Extract bit timing data tmp is in clocks per bit time */
tmp = AT32_PCLK1_FREQUENCY / bt->bt_baud; // <- div by 0
```
Instances found are listed in the *Location* section below. They are not shown in detail to reduce the length of the issue.
Ensure the attacker-controlled data is properly validated before use, to stop division by zero situations. For instance:
```c
DEBUGASSERT(bt->bt_baud > 0 && bt->bt_baud < AT32_PCLK1_FREQUENCY);
```
* arch/arm/src/stm32/stm32_fdcan.c
* arch/arm/src/stm32/stm32_can.c
* arch/arm/src/sama5/sam_mcan.c
* arch/arm/src/at32/at32_can.c
* arch/arm/src/samv7/sam_mcan.c
* arch/arm/src/stm32f0l0g0/stm32_fdcan.c
* arch/arm/src/stm32f7/stm32_can.c
* arch/arm/src/stm32h5/stm32_fdcan.c
* arch/arm/src/stm32l4/stm32l4_can.c
* arch/arm/src/tiva/common/tiva_can.c
* drivers/can/mcp2515.c
Signed-off-by: Catalin Visinescu <catalin_visinescu@yahoo.com>
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Apache NuttX is a real-time operating system (RTOS) with an emphasis on standards compliance and small footprint. Scalable from 8-bit to 64-bit microcontroller environments, the primary governing standards in NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and other common RTOSs (such as VxWorks) are adopted for functionality not available under these standards, or for functionality that is not appropriate for deeply-embedded environments (such as fork()).
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