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Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp filters

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On 10/20, Tycho Andersen wrote:
>
> +long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
> +			void __user *data)
> +{
> +	struct seccomp_filter *filter;
> +	struct sock_fprog_kern *fprog;
> +	long ret;
> +	unsigned long count = 0;
> +
> +	if (!capable(CAP_SYS_ADMIN) ||
> +	    current->seccomp.mode != SECCOMP_MODE_DISABLED) {
> +		return -EACCES;
> +	}
> +
> +	spin_lock_irq(&task->sighand->siglock);
> +	if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
> +		ret = -EINVAL;
> +		goto out_task;
> +	}
> +
> +	filter = task->seccomp.filter;
> +	while (filter) {
> +		filter = filter->prev;
> +		count++;
> +	}
> +
> +	if (filter_off >= count) {
> +		ret = -ENOENT;
> +		goto out_task;
> +	}
> +	count -= filter_off;
> +
> +	filter = task->seccomp.filter;
> +	while (filter && count > 1) {
> +		filter = filter->prev;
> +		count--;
> +	}
> +
> +	if (WARN_ON(count != 1)) {
> +		/* The filter tree shouldn't shrink while we're using it. */
> +		ret = -ENOENT;
> +		goto out_task;
> +	}
> +
> +	fprog = filter->prog->orig_prog;
> +	if (!fprog) {
> +		/* This must be a new non-cBPF filter, since we save every
> +		 * every cBPF filter's orig_prog above when
> +		 * CONFIG_CHECKPOINT_RESTORE is enabled.
> +		 */
> +		ret = -EMEDIUMTYPE;
> +		goto out_task;
> +	}
> +
> +	ret = fprog->len;
> +	if (!data)
> +		goto out_task;
> +
> +	if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog))) {
> +		ret = -EFAULT;
> +		goto out_task;
> +	}

Oh wait, I didn't notice this when I looked at v7.

No, you can't do copy_to_user() from atomic context. You need to pin this
filter, drop the lock/irq, then copy_to_user().

Oleg.

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v8 of seccomp filter c/r Tycho Andersen <tycho.andersen@canonical.com> - 2015-10-20 22:00 +0200
  [PATCH v8] seccomp, ptrace: add support for dumping seccomp filters Tycho Andersen <tycho.andersen@canonical.com> - 2015-10-20 22:00 +0200
    Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp filters Kees Cook <keescook@chromium.org> - 2015-10-20 22:30 +0200
      Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Tycho Andersen <tycho.andersen@canonical.com> - 2015-10-20 22:40 +0200
    Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Oleg Nesterov <oleg@redhat.com> - 2015-10-20 22:30 +0200
      Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Tycho Andersen <tycho.andersen@canonical.com> - 2015-10-21 00:10 +0200
        Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Oleg Nesterov <oleg@redhat.com> - 2015-10-21 21:00 +0200
          Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Tycho Andersen <tycho.andersen@canonical.com> - 2015-10-21 21:20 +0200
            Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp filters Kees Cook <keescook@chromium.org> - 2015-10-21 22:20 +0200
              Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp filters Daniel Borkmann <daniel@iogearbox.net> - 2015-10-21 22:20 +0200
                Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Tycho Andersen <tycho.andersen@canonical.com> - 2015-10-21 22:40 +0200
            Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Oleg Nesterov <oleg@redhat.com> - 2015-10-21 23:20 +0200
              Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp filters Kees Cook <keescook@chromium.org> - 2015-10-21 23:30 +0200
              Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Tycho Andersen <tycho.andersen@canonical.com> - 2015-10-21 23:40 +0200
                Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Oleg Nesterov <oleg@redhat.com> - 2015-10-25 15:50 +0100
                Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp filters Kees Cook <keescook@chromium.org> - 2015-10-26 07:50 +0100
                Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp filters Kees Cook <keescook@chromium.org> - 2015-10-26 08:10 +0100
                Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp  filters Tycho Andersen <tycho.andersen@canonical.com> - 2015-10-27 01:10 +0100
                Re: [PATCH v8] seccomp, ptrace: add support for dumping seccomp filters Daniel Borkmann <daniel@iogearbox.net> - 2015-10-27 01:20 +0100

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