linux-ext4 - Re: [PATCH] misc/fsck.c: Processes may kill other processes.

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Date:   Mon, 10 Oct 2022 09:17:25 +0200
From:   Lukas Czerner <lczerner@...hat.com>
To:     zhanchengbin <zhanchengbin1@...wei.com>
Cc:     Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
        liuzhiqiang26@...wei.com, linfeilong <linfeilong@...wei.com>
Subject: Re: [PATCH] misc/fsck.c: Processes may kill other processes.

On Sat, Oct 08, 2022 at 11:05:48AM +0800, zhanchengbin wrote:
> If run the fsck -N command, processes don't execute, just show what
> would be done. However, the pid whose value is -1 is added to the
> instance_list list in the execute function,if the kill_all function
> is called later, kill(-1, signum) is executed, Signals are sent to
> all processes except the number one process and itself. Other
> processes will be killed if they use the default signal processing
> function.
> 
> Signed-off-by: zhanchengbin <zhanchengbin1@...wei.com>
> ---
>  misc/fsck.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/misc/fsck.c b/misc/fsck.c
> index 4efe10ec..faf7789d 100644
> --- a/misc/fsck.c
> +++ b/misc/fsck.c
> @@ -546,6 +546,8 @@ static int kill_all(int signum)
>  	for (inst = instance_list; inst; inst = inst->next) {
>  		if (inst->flags & FLAG_DONE)
>  			continue;
> +		if (inst->pid == -1)
> +			continue;

That works, but I think we can afford to be a little defensive here.
Anything <= 0 is a bug and can have unexpected consequences if we
actually call the kill().

		if (inst->pid <= 0)
			continue;


Also as Darrick pointed out we need to send the patch to util-linux
(disk-utils/fsck.c) as well if you haven't already.

-Lukas


>  		kill(inst->pid, signum);
>  		n++;
>  	}
> -- 
> 2.27.0
>