Re: [Qemu-trivial] [Qemu-devel] [PATCH for 2.10 27/35] syscall: fix dereference of undefined pointer

[Peter Maydell]

On 24 July 2017 at 19:27, Philippe Mathieu-Daudé <address@hidden> wrote:
> Clang's scan-build-5.0 reports:
>
> linux-user/syscall.c:5581:9: warning: Dereference of undefined pointer value
>     if (*host_rt_dev_ptr != 0) {
>         ^~~~~~~~~~~~~~~~
>
> Reported-by: Clang Static Analyzer
> Suggested-by: Laurent Vivier <address@hidden>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>  linux-user/syscall.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index fcd20fa276..e79b5baec4 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -5524,7 +5524,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, 
> uint8_t *buf_temp,
>      int target_size;
>      void *argptr;
>      abi_ulong *target_rt_dev_ptr;
> -    unsigned long *host_rt_dev_ptr;
> +    unsigned long *host_rt_dev_ptr = NULL;
>      abi_long ret;
>      int i;
>
> @@ -5570,6 +5570,7 @@ static abi_long do_ioctl_rt(const IOCTLEntry *ie, 
> uint8_t *buf_temp,
>      unlock_user(argptr, arg, 0);
>
>      ret = get_errno(safe_ioctl(fd, ie->host_cmd, buf_temp));
> +    assert(host_rt_dev_ptr);

There's not much point in this assert because it doesn't
tell us anything we're not about to find out immediately
by dereferencing the pointer...

>      if (*host_rt_dev_ptr != 0) {
>          unlock_user((void *)*host_rt_dev_ptr,
>                      *target_rt_dev_ptr, 0);
> --
> 2.13.3

thanks
-- PMM