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SubjectRe: [PATCH 1/5] Split wait_noreap_copyout()
At Mon, 11 May 2009 15:25:50 +0200, Vitaly Mayatskikh wrote:
>
> Move getrusage() and put_user() code from wait_noreap_copyout()
> to copy_wait_opts_to_user(). The same code is spreaded across all
> wait_task_*() routines, it's better to reuse one copy.
>
> Signed-off-by: Vitaly Mayatskikh <v.mayatskih@gmail.com>
> ---
> kernel/exit.c | 39 +++++++++++++++++++++++----------------
> 1 files changed, 23 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 25782da..9546362 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1123,27 +1123,34 @@ static int eligible_child(struct wait_opts *wo, struct task_struct *p)
> return 1;
> }
>
> -static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
> - pid_t pid, uid_t uid, int why, int status)
> +static int copy_wait_opts_to_user(struct wait_opts *wo, struct task_struct *p,
> + pid_t pid, uid_t uid, int why, int status, int signal)
> {
> - struct siginfo __user *infop;
> + struct siginfo __user *infop = wo->wo_info;
> int retval = wo->wo_rusage
> ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
>
> + if (!retval && infop) {
> + retval = put_user(signal, &infop->si_signo);
...
> +static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
> + pid_t pid, uid_t uid, int why, int status)
> +{
> + int retval = copy_wait_opts_to_user(wo, p, pid, uid, why, status, SIGCHLD);
> put_task_struct(p);
> - infop = wo->wo_info;
> - if (!retval)
> - retval = put_user(SIGCHLD, &infop->si_signo);
...

Oleg has pointed me to broken behaviour here. Previously
wait_noreap_copyout was doing unconditional put_user and was returning
EFAULT when infop is NULL. Now it uses copy_wait_opts_to_user, which
checks infop and return NULL in the same case. This change is visible
from userspace in waitid() function.

There're 2 opportunities how to deal with new behaviour:

1. Assume wait_task_zombie had a bug previously, and let this patch go.
2. Fix copy_wait_opts_to_user to old behaviour by something like:

if (!retval && (infop || WNOWAIT)) {

What's your opinion?

--
wbr, Vitaly


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