Re: [patch V2 01/38] posix-cpu-timers: Provide task validation functions

[Frederic Weisbecker]

On Wed, Aug 21, 2019 at 09:08:48PM +0200, Thomas Gleixner wrote:
> The code contains three slightly different copies of validating whether a
> given clock resolves to a valid task and whether the current caller has
> permissions to access it.
> 
> Create central functions. Replace check_clock() as a first step and rename
> it to something sensible.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>  kernel/time/posix-cpu-timers.c |   65 +++++++++++++++++++++++++++--------------
>  1 file changed, 44 insertions(+), 21 deletions(-)
> 
> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -35,27 +35,52 @@ void update_rlimit_cpu(struct task_struc
>  	spin_unlock_irq(&task->sighand->siglock);
>  }
>  
> -static int check_clock(const clockid_t which_clock)
> +/*
> + * Functions for validating access to tasks.
> + */
> +static struct task_struct *lookup_task(const pid_t pid, bool thread)
>  {
> -	int error = 0;
>  	struct task_struct *p;
> -	const pid_t pid = CPUCLOCK_PID(which_clock);
>  
> -	if (CPUCLOCK_WHICH(which_clock) >= CPUCLOCK_MAX)
> -		return -EINVAL;
> +	if (!pid)
> +		return thread ? current : current->group_leader;
>  
> -	if (pid == 0)
> -		return 0;
> +	p = find_task_by_vpid(pid);
> +	if (!p || p == current)
> +		return p;

What if (p == current && !thread && !has_group_leader_pid(p)) ?

> +	if (thread)
> +		return same_thread_group(p, current) ? p : NULL;
> +	if (p == current)
> +		return p;

You already checked that above.

> +	return has_group_leader_pid(p) ? p : NULL;
> +}