linux-kernel - Re: [PATCH 2/2] ptrace: Return the signal to continue with from ptrace

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Date:   Thu, 17 Mar 2022 12:13:09 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexey Gladkov <legion@...nel.org>,
        Kyle Huey <me@...ehuey.com>, Oleg Nesterov <oleg@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>, linux-api@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 2/2] ptrace: Return the signal to continue with from
 ptrace_stop

On Tue, Mar 15, 2022 at 06:22:26PM -0500, Eric W. Biederman wrote:
> 
> The signal a task should continue with after a ptrace stop is
> inconsistently read, cleared, and sent.  Solve this by reading and
> clearing the signal to be sent in ptrace_stop.
> 
> In an ideal world everything except ptrace_signal would share a common
> implementation of continuing with the signal, so ptracers could count
> on the signal they ask to continue with actually being delivered.  For
> now retain bug compatibility and just return with the signal number
> the ptracer requested the code continue with.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>  include/linux/ptrace.h | 12 ++++++------
>  kernel/signal.c        | 31 ++++++++++++++++++-------------
>  2 files changed, 24 insertions(+), 19 deletions(-)
> 
> diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
> index 3e6b46e2b7be..15b3d176b6b4 100644
> --- a/include/linux/ptrace.h
> +++ b/include/linux/ptrace.h
> @@ -60,7 +60,7 @@ extern int ptrace_writedata(struct task_struct *tsk, char __user *src, unsigned
>  extern void ptrace_disable(struct task_struct *);
>  extern int ptrace_request(struct task_struct *child, long request,
>  			  unsigned long addr, unsigned long data);
> -extern void ptrace_notify(int exit_code, unsigned long message);
> +extern int ptrace_notify(int exit_code, unsigned long message);
> [...]
> -static void ptrace_stop(int exit_code, int why, int clear_code,
> +static int ptrace_stop(int exit_code, int why, int clear_code,
>  			unsigned long message, kernel_siginfo_t *info)
> [...]
> -static void ptrace_do_notify(int signr, int exit_code, int why, unsigned long message)
> +static int ptrace_do_notify(int signr, int exit_code, int why, unsigned long message)
> [...]
> -void ptrace_notify(int exit_code, unsigned long message)
> +int ptrace_notify(int exit_code, unsigned long message)

Just for robustness, how about marking the functions that have switched
from void to int return as __must_check (or at least just ptrace_notify)?

With that and the style nit Oleg already mentioned, yeah, this looks
good too.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook