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SubjectRe: [PATCH v3 05/11] rlimits: allow setrlimit to non-current tasks
On Mon, 10 May 2010 20:00:45 +0200
Jiri Slaby <jslaby@suse.cz> wrote:

> From: Jiri Slaby <jirislaby@gmail.com>
>
> Add locking to allow setrlimit accept task parameter other than
> current.
>
> Namely, lock tasklist_lock for read and check whether the task
> structure has sighand non-null. Do all the signal processing under
> that lock still held.
>
> Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> ---
> kernel/sys.c | 11 ++++++++++-
> 1 files changed, 10 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 7c76f84..eb21661 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1272,6 +1272,7 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,
>
> #endif
>
> +/* make sure you are allowed to change @tsk limits before calling this */
> int do_setrlimit(struct task_struct *tsk, unsigned int resource,
> struct rlimit *new_rlim)
> {
> @@ -1285,9 +1286,16 @@ int do_setrlimit(struct task_struct *tsk, unsigned int resource,
> if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open)
> return -EPERM;
>
> + /* protect tsk->signal and tsk->sighand from disappearing */
> + read_lock(&tasklist_lock);
> + if (!tsk->sighand) {
> + retval = -ESRCH;
> + goto out;
> + }
> +
> retval = security_task_setrlimit(tsk, resource, new_rlim);

I looked at the amount of code which exists under
security_task_setrlimit() and nearly died. Please convince me that it
is correct to do all that work under tasklist_lock, and that it is also
maintainable.

> update_rlimit_cpu(tsk, new_rlim->rlim_cur);
> out:
> + read_unlock(&tasklist_lock);

And this causes task-struct.sighand->siglock to be taken under
tasklist_lock. Was that a pre-existing ranking, or is it a new one?



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