Re: [PATCH 8/9] signal/task_exit: Use start_task_exit in place of do_exit

Kees Cook
2021-06-26T05:56:28Z

On Thu, Jun 24, 2021 at 02:03:25PM -0500, Eric W. Biederman wrote:
>
> Reuse start_task_exit_locked to implement start_task_exit.
>
> Simplify the exit logic by having all exits go through get_signal.
> This simplifies the analysis of syncrhonization during exit and
> gurantees a full set of registers will be available for ptrace to
> examine at PTRACE_EVENT_EXIT.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
> include/linux/sched/signal.h | 1 +
> kernel/exit.c | 4 +++-
> kernel/seccomp.c | 2 +-
> kernel/signal.c | 12 ++++++++++++
> 4 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
> index a958381ba4a9..3f4e69c019b7 100644
> --- a/include/linux/sched/signal.h
> +++ b/include/linux/sched/signal.h
> @@ -430,6 +430,7 @@ static inline void ptrace_signal_wake_up(struct task_struct *t, bool resume)
>
> void start_group_exit(int exit_code);
> void start_task_exit_locked(struct task_struct *task, int exit_code);
> +void start_task_exit(int exit_code);
>
> void task_join_group_stop(struct task_struct *task);
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 635f434122b7..51e0c82b3f7d 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -889,7 +889,9 @@ EXPORT_SYMBOL(complete_and_exit);
>
> SYSCALL_DEFINE1(exit, int, error_code)
> {
> - do_exit((error_code&0xff)<<8);
> + start_task_exit((error_code&0xff)<<8);
> + /* get_signal will call do_exit */
> + return 0;
> }
>
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index b1c06fd1b205..e0c4c123a8bf 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -1248,7 +1248,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
> force_sig_seccomp(this_syscall, data, true);
> } else {
> if (action == SECCOMP_RET_KILL_THREAD)
> - do_exit(SIGSYS);
> + start_task_exit(SIGSYS);
> else
> start_group_exit(SIGSYS);
> }

Looks good, yeah.

> diff --git a/kernel/signal.c b/kernel/signal.c
> index afbc001220dd..63fda9b6bbf9 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1424,6 +1424,18 @@ void start_task_exit_locked(struct task_struct *task, int exit_code)
> }
> }
>
> +void start_task_exit(int exit_code)
> +{
> + struct task_struct *task = current;
> + if (!fatal_signal_pending(task)) {
> + struct sighand_struct *const sighand = task->sighand;
> + spin_lock_irq(&sighand->siglock);
> + if (!fatal_signal_pending(current))

efficiency nit: "task" instead of "current" here, yes?

> + start_task_exit_locked(task, exit_code);
> + spin_unlock_irq(&sighand->siglock);
> + }
> +}
> +
> struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
> unsigned long *flags)
> {
> --
> 2.20.1
>

--
Kees Cook