From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2427DCA9EC7 for ; Wed, 30 Oct 2019 15:32:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F16872087F for ; Wed, 30 Oct 2019 15:32:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727319AbfJ3PcG (ORCPT ); Wed, 30 Oct 2019 11:32:06 -0400 Received: from www62.your-server.de ([213.133.104.62]:38936 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727201AbfJ3PcG (ORCPT ); Wed, 30 Oct 2019 11:32:06 -0400 Received: from [2a02:120b:2c12:c120:71a0:62dd:894c:fd0e] (helo=localhost) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1iPpx5-0004rK-TU; Wed, 30 Oct 2019 16:32:03 +0100 Date: Wed, 30 Oct 2019 16:32:03 +0100 From: Daniel Borkmann To: Andrii Nakryiko Cc: Wenbo Zhang , bpf , Yonghong Song , Networking Subject: Re: [PATCH bpf-next v4] bpf: add new helper fd2path for mapping a file descriptor to a pathname Message-ID: <20191030153203.GA2675@pc-63.home> References: <20191028141053.12267-1-ethercflow@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.101.4/25618/Wed Oct 30 09:54:22 2019) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Oct 29, 2019 at 11:48:44AM -0700, Andrii Nakryiko wrote: > On Mon, Oct 28, 2019 at 1:59 PM Wenbo Zhang wrote: > > > > When people want to identify which file system files are being opened, > > read, and written to, they can use this helper with file descriptor as > > input to achieve this goal. Other pseudo filesystems are also supported. > > > > This requirement is mainly discussed here: > > > > https://github.com/iovisor/bcc/issues/237 > > > > v3->v4: > > - fix missing fdput() > > - move fd2path from kernel/bpf/trace.c to kernel/trace/bpf_trace.c > > - move fd2path's test code to another patch > > > > v2->v3: > > - remove unnecessary LOCKDOWN_BPF_READ > > - refactor error handling section for enhanced readability > > - provide a test case in tools/testing/selftests/bpf > > > > v1->v2: > > - fix backward compatibility > > - add this helper description > > - fix signed-off name > > > > Signed-off-by: Wenbo Zhang > > --- > > include/uapi/linux/bpf.h | 14 +++++++++++- > > kernel/trace/bpf_trace.c | 40 ++++++++++++++++++++++++++++++++++ > > tools/include/uapi/linux/bpf.h | 14 +++++++++++- > > 3 files changed, 66 insertions(+), 2 deletions(-) > > > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > > index 4af8b0819a32..124632b2a697 100644 > > --- a/include/uapi/linux/bpf.h > > +++ b/include/uapi/linux/bpf.h > > @@ -2775,6 +2775,17 @@ union bpf_attr { > > * restricted to raw_tracepoint bpf programs. > > * Return > > * 0 on success, or a negative error in case of failure. > > + * > > + * int bpf_fd2path(char *path, u32 size, int fd) > > from what I can see, we don't have any BPF helper with this naming > approach(2 -> to, 4 -> for, etc). How about something like > bpf_get_file_path? > > > + * Description > > + * Get **file** atrribute from the current task by *fd*, then call > > + * **d_path** to get it's absolute path and copy it as string into > > + * *path* of *size*. The **path** also support pseudo filesystems > > + * (whether or not it can be mounted). The *size* must be strictly > > + * positive. On success, the helper makes sure that the *path* is > > + * NUL-terminated. On failure, it is filled with zeroes. > > + * Return > > + * 0 on success, or a negative error in case of failure. > > Mention that we actually return a positive number on success, which is > a size of the string + 1 for NUL byte (the +1 is not true right now, > but I think should be). > > > */ > > #define __BPF_FUNC_MAPPER(FN) \ > > FN(unspec), \ > > @@ -2888,7 +2899,8 @@ union bpf_attr { > > FN(sk_storage_delete), \ > > FN(send_signal), \ > > FN(tcp_gen_syncookie), \ > > - FN(skb_output), > > + FN(skb_output), \ > > + FN(fd2path), > > > > /* integer value in 'imm' field of BPF_CALL instruction selects which helper > > * function eBPF program intends to call > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > > index 571c25d60710..dd7b070df3d6 100644 > > --- a/kernel/trace/bpf_trace.c > > +++ b/kernel/trace/bpf_trace.c > > @@ -683,6 +683,44 @@ static const struct bpf_func_proto bpf_send_signal_proto = { > > .arg1_type = ARG_ANYTHING, > > }; > > > > +BPF_CALL_3(bpf_fd2path, char *, dst, u32, size, int, fd) > > +{ > > + struct fd f; > > + char *p; > > + int ret = -EINVAL; > > + > > + /* Use fdget_raw instead of fdget to support O_PATH */ > > + f = fdget_raw(fd); > > I haven't followed previous discussions, so sorry if this was asked > before. Can either fdget_raw or d_path sleep? Also, d_path seems to be > relying on current, which in the interrupt context might not be what > you really want. Have you considered these problems? > > > + if (!f.file) > > + goto error; > > + > > + p = d_path(&f.file->f_path, dst, size); > > + if (IS_ERR_OR_NULL(p)) { > > + ret = PTR_ERR(p); > > if p can really be NULL, you'd get ret == 0 here, which is probably > not what you want. > But reading d_path, it seems like it's either valid pointer or error, > so just use IS_ERR above? > > > + goto error; > > + } > > + > > + ret = strlen(p); > > + memmove(dst, p, ret); > > + dst[ret] = '\0'; > > I think returning number of useful bytes (including terminating NUL) > is good and follows bpf_probe_read_str() convention. So ret++ here? > > > + goto end; > > + > > +error: > > + memset(dst, '0', size); > > +end: > > + fdput(f); Also I'd prefer fdget_*()'s error path not calling fdput(f). > > + return ret; > > +} > > + > > [...]