2022-10-16 15:47:36

by Dawei Li

Subject: [PATCH] um: protect find_task_by_pid_ns() with rcu lock

find_task_by_pid_ns() is safe if and only if it's under protection
from rcu read lock, implements the protection.

base-commit: 193cb8372424184dde28088a4230a5fed0afb0ad

Signed-off-by: Dawei Li <[email protected]>
---
arch/um/drivers/mconsole_kern.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
index 5026e7b9adfe..6b80e766ae80 100644
--- a/arch/um/drivers/mconsole_kern.c
+++ b/arch/um/drivers/mconsole_kern.c
@@ -683,7 +683,10 @@ void mconsole_stack(struct mc_request *req)
return;
}

+ rcu_read_lock();
to = find_task_by_pid_ns(pid_requested, &init_pid_ns);
+ rcu_read_unlock();
+
if ((to == NULL) || (pid_requested == 0)) {
mconsole_reply(req, "Couldn't find that pid", 1, 0);
return;
--
2.25.1

2022-10-16 18:11:59

by Johannes Berg

Subject: Re: [PATCH] um: protect find_task_by_pid_ns() with rcu lock

On Sun, 2022-10-16 at 23:10 +0800, Dawei Li wrote:
> find_task_by_pid_ns() is safe if and only if it's under protection
> from rcu read lock, implements the protection.
>
> base-commit: 193cb8372424184dde28088a4230a5fed0afb0ad
>
> Signed-off-by: Dawei Li <[email protected]>
> ---
> arch/um/drivers/mconsole_kern.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
> index 5026e7b9adfe..6b80e766ae80 100644
> --- a/arch/um/drivers/mconsole_kern.c
> +++ b/arch/um/drivers/mconsole_kern.c
> @@ -683,7 +683,10 @@ void mconsole_stack(struct mc_request *req)
> return;
> }
>
> + rcu_read_lock();
> to = find_task_by_pid_ns(pid_requested, &init_pid_ns);
> + rcu_read_unlock();
> +
> if ((to == NULL) || (pid_requested == 0)) {
> mconsole_reply(req, "Couldn't find that pid", 1, 0);
> return;

This can't be right - the 'to' pointer is used later in the code (not in
the existing context), so the protection, if needed, would have to
include the later "with_console()" call?

johannes