[2/2] linux: clock_settime: Return proper value when passing NULL pointer

  When in __clock_settime function (__TIMESIZE != 64) the const struct
timespec's *tp pointer is NULL, the Linux kernel syscall returns
-EFAULT.
Without this patch the glibc crashes (when dereferencing NULL pointer)
as the Linux kernel syscall is not reached at all.

There is no need for such check in the __clock_settime64, as this
pointer either goes directly to Linux kernel or the pointer to local
copy is used (ts64).
---
 sysdeps/unix/sysv/linux/clock_settime.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
  

On Fri, Nov 8, 2019 at 7:34 AM Lukasz Majewski <lukma@denx.de> wrote:
>
> When in __clock_settime function (__TIMESIZE != 64) the const struct
> timespec's *tp pointer is NULL, the Linux kernel syscall returns
> -EFAULT.
> Without this patch the glibc crashes (when dereferencing NULL pointer)
> as the Linux kernel syscall is not reached at all.
>
> There is no need for such check in the __clock_settime64, as this
> pointer either goes directly to Linux kernel or the pointer to local
> copy is used (ts64).

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  sysdeps/unix/sysv/linux/clock_settime.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/sysdeps/unix/sysv/linux/clock_settime.c b/sysdeps/unix/sysv/linux/clock_settime.c
> index 6706dbb31f..e358a18998 100644
> --- a/sysdeps/unix/sysv/linux/clock_settime.c
> +++ b/sysdeps/unix/sysv/linux/clock_settime.c
> @@ -51,7 +51,14 @@ __clock_settime64 (clockid_t clock_id, const struct __timespec64 *tp)
>  int
>  __clock_settime (clockid_t clock_id, const struct timespec *tp)
>  {
> -  struct __timespec64 ts64 = valid_timespec_to_timespec64 (*tp);
> +  struct __timespec64 ts64;
> +
> +  if (tp == NULL)
> +    {
> +      __set_errno (EFAULT);
> +      return -1;
> +    }
> +  ts64 = valid_timespec_to_timespec64 (*tp);
>
>    return __clock_settime64 (clock_id, &ts64);
>  }
> --
> 2.20.1
>
  

On Fri, 8 Nov 2019, Alistair Francis wrote:

> On Fri, Nov 8, 2019 at 7:34 AM Lukasz Majewski <lukma@denx.de> wrote:
> >
> > When in __clock_settime function (__TIMESIZE != 64) the const struct
> > timespec's *tp pointer is NULL, the Linux kernel syscall returns
> > -EFAULT.
> > Without this patch the glibc crashes (when dereferencing NULL pointer)
> > as the Linux kernel syscall is not reached at all.
> >
> > There is no need for such check in the __clock_settime64, as this
> > pointer either goes directly to Linux kernel or the pointer to local
> > copy is used (ts64).
> 
> Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

This patch is contrary to glibc conventions.  There is explicitly no 
guarantee of whether a segfault or EFAULT occurs when a function is called 
with invalid arguments.  There should be no explicit checks for NULL 
pointers in cases where a segfault will reliably occur otherwise and any 
existing such checks should be removed from glibc.

https://sourceware.org/glibc/wiki/Style_and_Conventions#Invalid_pointers

(And note the POSIX specification of EFAULT, "The reliable detection of 
this error cannot be guaranteed, and when not detected may result in the 
generation of a signal, indicating an address violation, which is sent to 
the process.".)