linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Christian Brauner <christian.brauner@ubuntu.com>
To: Sargun Dhillon <sargun@sargun.me>, oleg@redhat.com
Cc: linux-kernel@vger.kernel.org,
	containers@lists.linux-foundation.org, linux-api@vger.kernel.org,
	tycho@tycho.ws
Subject: Re: [RFC PATCH] ptrace: add PTRACE_GETFD request
Date: Fri, 6 Dec 2019 09:25:40 +0100	[thread overview]
Message-ID: <20191206082539.gmefytwu3ylixj5d@wittgenstein> (raw)
In-Reply-To: <20191205234450.GA26369@ircssh-2.c.rugged-nimbus-611.internal>

[+ Oleg, the maintainer. This needs to see his review before anything
 can happen to this series.]

On Thu, Dec 05, 2019 at 11:44:53PM +0000, Sargun Dhillon wrote:
> PTRACE_GETFD is a generic ptrace API that allows the tracer to
> get file descriptors from the traceee.
> 
> The primary reason to use this syscall is to allow sandboxers to
> take action on an FD on behalf of the tracee. For example, this
> can be combined with seccomp's user notification feature to extract
> a file descriptor and call privileged syscalls, like binding
> a socket to a privileged port.
> 
> Signed-off-by: Sargun Dhillon <sargun@sargun.me>
> ---
>  include/uapi/linux/ptrace.h |  5 +++++
>  kernel/ptrace.c             | 39 +++++++++++++++++++++++++++++++++++--
>  2 files changed, 42 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
> index a71b6e3b03eb..2b69f759826a 100644
> --- a/include/uapi/linux/ptrace.h
> +++ b/include/uapi/linux/ptrace.h
> @@ -101,6 +101,11 @@ struct ptrace_syscall_info {
>  	};
>  };
>  
> +/* This gets a file descriptor from a running process. It doesn't require the
> + * process to be stopped.
> + */
> +#define PTRACE_GETFD	0x420f
> +
>  /*
>   * These values are stored in task->ptrace_message
>   * by tracehook_report_syscall_* to describe the current syscall-stop.
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index cb9ddcc08119..a1d7b289fe8e 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -31,6 +31,7 @@
>  #include <linux/cn_proc.h>
>  #include <linux/compat.h>
>  #include <linux/sched/signal.h>
> +#include <linux/fdtable.h>
>  
>  #include <asm/syscall.h>	/* for syscall_get_* */
>  
> @@ -994,6 +995,37 @@ ptrace_get_syscall_info(struct task_struct *child, unsigned long user_size,
>  }
>  #endif /* CONFIG_HAVE_ARCH_TRACEHOOK */
>  
> +static int ptrace_getfd(struct task_struct *child, unsigned long fd)
> +{
> +	struct files_struct *files;
> +	struct file *file;
> +	int ret = 0;
> +
> +	files = get_files_struct(child);
> +	if (!files)
> +		return -ENOENT;
> +
> +	spin_lock(&files->file_lock);
> +	file = fcheck_files(files, fd);
> +	if (!file)
> +		ret = -EBADF;
> +	else
> +		get_file(file);
> +	spin_unlock(&files->file_lock);
> +	put_files_struct(files);
> +
> +	if (ret)
> +		goto out;
> +
> +	ret = get_unused_fd_flags(0);
> +	if (ret >= 0)
> +		fd_install(ret, file);
> +
> +	fput(file);
> +out:
> +	return ret;
> +}
> +
>  int ptrace_request(struct task_struct *child, long request,
>  		   unsigned long addr, unsigned long data)
>  {
> @@ -1222,7 +1254,9 @@ int ptrace_request(struct task_struct *child, long request,
>  	case PTRACE_SECCOMP_GET_METADATA:
>  		ret = seccomp_get_metadata(child, addr, datavp);
>  		break;
> -
> +	case PTRACE_GETFD:
> +		ret = ptrace_getfd(child, data);
> +		break;
>  	default:
>  		break;
>  	}
> @@ -1265,7 +1299,8 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
>  	}
>  
>  	ret = ptrace_check_attach(child, request == PTRACE_KILL ||
> -				  request == PTRACE_INTERRUPT);
> +				  request == PTRACE_INTERRUPT ||
> +				  request == PTRACE_GETFD);
>  	if (ret < 0)
>  		goto out_put_task_struct;
>  
> -- 
> 2.20.1
> 

  parent reply	other threads:[~2019-12-06  8:25 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-05 23:44 Sargun Dhillon
2019-12-06  2:38 ` Jann Horn
2019-12-06  6:16   ` Sargun Dhillon
2019-12-06  6:52     ` Aleksa Sarai
2019-12-06  8:25 ` Christian Brauner [this message]
2019-12-06 12:23   ` Oleg Nesterov
2019-12-06 14:10 ` Tycho Andersen
2019-12-06 19:03   ` Sargun Dhillon
2019-12-06 19:05     ` Jann Horn
2019-12-06 19:05       ` Jann Horn
2019-12-06 20:45 ` Andy Lutomirski

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191206082539.gmefytwu3ylixj5d@wittgenstein \
    --to=christian.brauner@ubuntu.com \
    --cc=containers@lists.linux-foundation.org \
    --cc=linux-api@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=oleg@redhat.com \
    --cc=sargun@sargun.me \
    --cc=tycho@tycho.ws \
    --subject='Re: [RFC PATCH] ptrace: add PTRACE_GETFD request' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).