Re: [PATCH] signal: avoid shared siginfo namespace rewrites

[Oleg Nesterov]

On 06/22, Bradley Morgan wrote:
>
> send_signal_locked() rewrites sender ids for the target namespace.
> Group sends reuse the same siginfo, so one recipient can affect the
> next.

Hmm... I'll re-read this change tomorrow after sleep, but I am almost sure
you are you are right anyway...

I am wondering if we can conditionalize the "swap(rewritten, info)" logic
with your patch, most probably this makes no sense...

May I suggest another change on top of your fix? Make the "kernel_siginfo *info"
arg of send_signal_locked() "const". To make it more clear. Yes, the signature
of has_si_pid_and_uid() should be changed too. Up to you.

Thanks,

Oleg.

> Copy the siginfo before changing it.
>
> Fixes: 7a0cf094944e ("signal: Correct namespace fixups of si_pid and si_uid")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Bradley Morgan <include@xxxxxxxxx>
> ---
>  kernel/signal.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/kernel/signal.c b/kernel/signal.c
> index b9fc7be1a169..d72d9be3a992 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -1181,6 +1181,7 @@ static inline bool has_si_pid_and_uid(struct kernel_siginfo *info)
>  int send_signal_locked(int sig, struct kernel_siginfo *info,
>  		       struct task_struct *t, enum pid_type type)
>  {
> +	struct kernel_siginfo rewritten;
>  	/* Should SIGKILL or SIGSTOP be received by a pid namespace init? */
>  	bool force = false;
> 
> @@ -1194,6 +1195,9 @@ int send_signal_locked(int sig, struct kernel_siginfo *info,
>  		/* SIGKILL and SIGSTOP is special or has ids */
>  		struct user_namespace *t_user_ns;
> 
> +		rewritten = *info;
> +		info = &rewritten;
> +
>  		rcu_read_lock();
>  		t_user_ns = task_cred_xxx(t, user_ns);
>  		if (current_user_ns() != t_user_ns) {
> --
> 2.53.0
>