On Mon, Apr 22, 2024 at 11:41:40PM +0700, Bui Quang Minh wrote:
> Currently, we allocate a lbuf-sized kernel buffer and copy lbuf from
> userspace to that buffer. Later, we use scanf on this buffer but we don't
> ensure that the string is terminated inside the buffer, this can lead to
> OOB read when using scanf. Fix this issue by allocating 1 more byte to at
> the end of buffer and write NULL terminator to the end of buffer after
> userspace copying.
>
> Fixes: a4f17cc72671 ("s390/cio: add CRW inject functionality")
> Signed-off-by: Bui Quang Minh <minhquangbui99@xxxxxxxxx>
> ---
> drivers/s390/cio/cio_inject.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/s390/cio/cio_inject.c b/drivers/s390/cio/cio_inject.c
> index 8613fa937237..9b69fbf49f60 100644
> --- a/drivers/s390/cio/cio_inject.c
> +++ b/drivers/s390/cio/cio_inject.c
> @@ -95,10 +95,11 @@ static ssize_t crw_inject_write(struct file *file, const char __user *buf,
> return -EINVAL;
> }
>
> - buffer = vmemdup_user(buf, lbuf);
> + buffer = vmemdup_user(buf, lbuf + 1);
> if (IS_ERR(buffer))
> return -ENOMEM;
>
> + buffer[lbuf] = '\0';
This would read one byte too much from user space, and could potentially
fault.
Why isn't this simply memdup_user_nul() like all others, which would do the
right thing?
