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Date:   Tue, 4 Apr 2017 23:57:31 +0900
From:   Akinobu Mita <akinobu.mita@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH v2] fault-inject: support systematic fault injection

2017-03-28 22:01 GMT+09:00 Dmitry Vyukov <dvyukov@...gle.com>:
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 6e8655845830..66001172249b 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1353,6 +1353,53 @@ static const struct file_operations proc_fault_inject_operations = {
>         .write          = proc_fault_inject_write,
>         .llseek         = generic_file_llseek,
>  };
> +
> +static ssize_t proc_fail_nth_write(struct file *file, const char __user *buf,
> +                                  size_t count, loff_t *ppos)
> +{
> +       struct task_struct *task;
> +       int err, n;
> +
> +       task = get_proc_task(file_inode(file));
> +       if (!task)
> +               return -ESRCH;
> +       put_task_struct(task);
> +       if (task != current)
> +               return -EPERM;
> +       err = kstrtoint_from_user(buf, count, 10, &n);
> +       if (err)
> +               return err;
> +       if (n < 0 || n == INT_MAX)
> +               return -EINVAL;
> +       current->fail_nth = n + 1;
> +       return len;
> +}
> +
> +static ssize_t proc_fail_nth_read(struct file *file, char __user *buf,
> +                                 size_t count, loff_t *ppos)
> +{
> +       struct task_struct *task;
> +       int err;
> +
> +       task = get_proc_task(file_inode(file));
> +       if (!task)
> +               return -ESRCH;
> +       put_task_struct(task);
> +       if (task != current)
> +               return -EPERM;
> +       if (count < 1)
> +               return -EINVAL;
> +       err = put_user((char)(current->fail_nth ? 'N' : 'Y'), buf);
> +       if (err)
> +               return err;
> +       current->fail_nth = 0;
> +       return 1;
> +}
> +
> +static const struct file_operations proc_fail_nth_operations = {
> +       .read           = proc_fail_nth_read,
> +       .write          = proc_fail_nth_write,
> +};
>  #endif
>
>
> @@ -3296,6 +3343,11 @@ static const struct pid_entry tid_base_stuff[] = {
>  #endif
>  #ifdef CONFIG_FAULT_INJECTION
>         REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
> +       /*
> +        * Operations on the file check that the task is current,
> +        * so we create it with 0666 to support testing under unprivileged user.
> +        */
> +       REG("fail-nth", 0666, proc_fail_nth_operations),
>  #endif

This file is owned by the currnet user.  So we can create it with 0644
and just allow unprivileged user to write it.  And it enables to remove
the check that the task is current or not in read/write operations.

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