Re: [PATCH] linux-user: Fix Coverity CID 1430271 / CID 1430272

[Peter Maydell]

On Thu, 9 Jul 2020 at 21:00, Laurent Vivier <laurent@vivier.eu> wrote:
>
> In new functions print_ioctl() and print_syscall_ret_ioctl(), we don't
> check if lock_user() returns NULL and this would cause a segfault in
> thunk_print().
>
> If lock_user() returns NULL don't call thunk_print() but prints only the
> value of the (invalid) pointer.
>
> Tested with:
>
>     # cat ioctl.c
>     #include <unistd.h>
>     #include <sys/ioctl.h>
>
>     int main(void)
>     {
>         int ret;
>
>         ret = ioctl(STDOUT_FILENO, TCGETS, 0xdeadbeef);
>         ret = ioctl(STDOUT_FILENO, TCSETSF, 0xdeadbeef);
>         return 0;
>     }
>     # QEMU_STRACE= ./ioctl
>     ...
>     578 ioctl(1,TCGETS,0xdeadbeef) = -1 errno=2 (Bad address)
>     578 ioctl(1,TCSETSF,0xdeadbeef) = -1 errno=2 (Bad address)
>     ...
>     # QEMU_STRACE= passwd
>     ...
>     623 ioctl(0,TCGETS,0x3fffed04) = 0 ({})
>     623 ioctl(0,TCSETSF,{}) = 0
>     ...
>
> Reported-by: Peter Maydell <peter.maydell@linaro.org>
> Fixes: 79482e5987c8 ("linux-user: Add strace support for printing arguments 
> of ioctl()")
> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
> ---
>  linux-user/strace.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/linux-user/strace.c b/linux-user/strace.c
> index 5235b2260cdd..39554d903911 100644
> --- a/linux-user/strace.c
> +++ b/linux-user/strace.c
> @@ -889,8 +889,12 @@ print_syscall_ret_ioctl(const struct syscallname *name, 
> abi_long ret,
>              arg_type++;
>              target_size = thunk_type_size(arg_type, 0);
>              argptr = lock_user(VERIFY_READ, arg2, target_size, 1);
> -            thunk_print(argptr, arg_type);
> -            unlock_user(argptr, arg2, target_size);
> +            if (argptr) {
> +                thunk_print(argptr, arg_type);
> +                unlock_user(argptr, arg2, target_size);
> +            } else {
> +                print_pointer(arg2, 1);
> +            }
>              qemu_log(")");
>          }
>      }
> @@ -3119,8 +3123,12 @@ print_ioctl(const struct syscallname *name,
>                      arg_type++;
>                      target_size = thunk_type_size(arg_type, 0);
>                      argptr = lock_user(VERIFY_READ, arg2, target_size, 1);
> -                    thunk_print(argptr, arg_type);
> -                    unlock_user(argptr, arg2, target_size);
> +                    if (argptr) {
> +                        thunk_print(argptr, arg_type);
> +                        unlock_user(argptr, arg2, target_size);
> +                    } else {
> +                        print_pointer(arg2, 1);
> +                    }
>                      break;
>                  }
>                  break;

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM