On Fri, Sep 06, 2024 at 10:11:03PM +0800, Edward Adam Davis wrote:
> The syzbot reported a kernel-usb-infoleak in usbtmc_write.
>
> The expression "aligned = (transfersize + (USBTMC_HEADER_SIZE + 3)) & ~3;"
> in usbtmcw_write() follows the following pattern:
>
> aligned = (1 + 12 + 3) & ~3 = 16 // 3 bytes have not been initialized
> aligned = (2 + 12 + 3) & ~3 = 16 // 2 bytes have not been initialized
> aligned = (3 + 12 + 3) & ~3 = 16 // 1 byte has not been initialized
> aligned = (4 + 12 + 3) & ~3 = 16 // All bytes have been initialized
> aligned = (5 + 12 + 3) & ~3 = 20 // 3 bytes have not been initialized
> aligned = (6 + 12 + 3) & ~3 = 20 // 2 bytes have not been initialized
> aligned = (7 + 12 + 3) & ~3 = 20 // 1 byte has not been initialized
> aligned = (8 + 12 + 3) & ~3 = 20 // All bytes have been initialized
> aligned = (9 + 12 + 3) & ~3 = 24
> ...
What is the purpose of aligned? Why doesn't the driver simply use
USBTMC_HEADER_SIZE + transfersize instead of rounding it up to a
multiple of 4?
> Note: #define USBTMC_HEADER_SIZE 12
>
> This results in the buffer[USBTMC_SEAD_SIZE+transfersize] and its
> subsequent memory not being initialized.
>
> The condition aligned < buflen is used to avoid out of bounds access to
> the buffer[USBTMC_HEADER_SIZE + transfersize] when "transfersize =
> buflen - USBTMC_HEADER_SIZE".
>
> Fixes: 4ddc645f40e9 ("usb: usbtmc: Add ioctl for vendor specific write")
> Reported-and-tested-by: syzbot+9d34f80f841e948c3fdb@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=9d34f80f841e948c3fdb
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
> ---
> drivers/usb/class/usbtmc.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/usb/class/usbtmc.c b/drivers/usb/class/usbtmc.c
> index 6bd9fe565385..faf8c5508997 100644
> --- a/drivers/usb/class/usbtmc.c
> +++ b/drivers/usb/class/usbtmc.c
> @@ -1591,6 +1591,10 @@ static ssize_t usbtmc_write(struct file *filp, const char __user *buf,
> goto exit;
> }
>
> + if (aligned < buflen && (transfersize % 4))
Shouldn't this be
if (USBTMC_HEADER_SIZE + transfersize < aligned)
?
Alan Stern
> + memset(&buffer[USBTMC_HEADER_SIZE + transfersize], 0,
> + aligned - USBTMC_HEADER_SIZE - transfersize);
> +
> dev_dbg(&data->intf->dev, "%s(size:%u align:%u)\n", __func__,
> (unsigned int)transfersize, (unsigned int)aligned);
>
> --
> 2.43.0
