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=-11.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 9B094CA9ED2 for ; Sun, 3 Nov 2019 04:10:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B86F214DA for ; Sun, 3 Nov 2019 04:10:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="hmTT9LS/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726558AbfKCEKU (ORCPT ); Sun, 3 Nov 2019 00:10:20 -0400 Received: from mail-vk1-f195.google.com ([209.85.221.195]:44144 "EHLO mail-vk1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726083AbfKCEKU (ORCPT ); Sun, 3 Nov 2019 00:10:20 -0400 Received: by mail-vk1-f195.google.com with SMTP id o198so3058059vko.11; Sat, 02 Nov 2019 21:10:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=eXpTsU66lBUFg+QMEodac4wkDqyVDWl6oCipcHR7lyM=; b=hmTT9LS/Ibk5gPKcf+3EYrV1Q9XTupah9+UfKNDNX8I2IzzACyWbJtmn2f+WsUv4W3 AFwj/ZljyyODN1j4NLwI2GT3xvLHzLYKsg9hFMF6lPqRKvrE2eAZG/OnbqZnA/9CG2dc ZeNTb7adL78o6iKZaH8FKxkstzyvUuHE6CXlYOx0kKOraLv7xhxLAK2WzJRMq30Ap/rW dO1/250ToiErjVPP4BXbzkQremLT8Z5v0QKqZhjkLswSpbZ0lP2+tZdKqojIcqAIlFq/ 5waOolHmVYC1CnUYVEQ4y2bXtwvE2jbq0WhxeWi2m5kuvJk7DcCO5qPzyZIPDLMkLv3h m+hQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=eXpTsU66lBUFg+QMEodac4wkDqyVDWl6oCipcHR7lyM=; b=ksSV7aRSJJF110vaAtM1IQTelNTLHi3VFC4M1yQUCF7XGTxVo3Je/YQvJVSKjMZuNP LH1h/v2Xd0J34izU79LUh4SAnhE2nPHCxDliRvsHKGjiU7pXLjxHE12Kw7GYV60KC/ET tKC/7JNjvPDXcTia3z8a3Q5pc485zN0otVyKMS5aUbhtp8kknh3krAMYMIOKVOrZt2Qo dHeaz1gX8hOLG/6fRLdwVlr1Bsjx4zO6Ni8s1Tlz5hpAUevlfgg6c3VH4P3No0kz4Wzb aomojcqp+WDeGMux/5gU3f/sQuoZEAPUXyclc1JvejD0u82HUiNlRCu2Phv4EOugygT/ CeBA== X-Gm-Message-State: APjAAAUdk4q6eYiydnSnRkJv47XjquuI6dMKLaquYXskKKiUEKNUj1Ce dATmwt4dgOW+Cb9Ddvr2KmGcwqXX/l0fhEaJzp0= X-Google-Smtp-Source: APXvYqyqLk93V1xrcDCv2pELafOa0yIImCfWvjPfCyzz3T6+30cdIhqMuR54sMZgDXc1hoIt6MZXrVCkjH3XBjwYrSE= X-Received: by 2002:a1f:944a:: with SMTP id w71mr1041716vkd.60.1572754219108; Sat, 02 Nov 2019 21:10:19 -0700 (PDT) MIME-Version: 1.0 References: <20191028141053.12267-1-ethercflow@gmail.com> <20191030153203.GA2675@pc-63.home> In-Reply-To: <20191030153203.GA2675@pc-63.home> From: Wenbo Zhang Date: Sun, 3 Nov 2019 12:10:15 +0800 Message-ID: Subject: Re: [PATCH bpf-next v4] bpf: add new helper fd2path for mapping a file descriptor to a pathname To: Daniel Borkmann Cc: Andrii Nakryiko , bpf , Yonghong Song , Networking Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org > Also I'd prefer fdget_*()'s error path not calling fdput(f). Thank you, I've committed a new patch to fix this. Daniel Borkmann =E4=BA=8E2019=E5=B9=B410=E6=9C=8830= =E6=97=A5=E5=91=A8=E4=B8=89 =E4=B8=8B=E5=8D=8811:32=E5=86=99=E9=81=93=EF=BC= =9A > > On Tue, Oct 29, 2019 at 11:48:44AM -0700, Andrii Nakryiko wrote: > > On Mon, Oct 28, 2019 at 1:59 PM Wenbo Zhang wrot= e: > > > > > > When people want to identify which file system files are being opened= , > > > read, and written to, they can use this helper with file descriptor a= s > > > input to achieve this goal. Other pseudo filesystems are also support= ed. > > > > > > 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 s= tring into > > > + * *path* of *size*. The **path** also support pseudo fi= lesystems > > > + * (whether or not it can be mounted). The *size* must b= e 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 whic= h 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_sign= al_proto =3D { > > > .arg1_type =3D ARG_ANYTHING, > > > }; > > > > > > +BPF_CALL_3(bpf_fd2path, char *, dst, u32, size, int, fd) > > > +{ > > > + struct fd f; > > > + char *p; > > > + int ret =3D -EINVAL; > > > + > > > + /* Use fdget_raw instead of fdget to support O_PATH */ > > > + f =3D 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 =3D d_path(&f.file->f_path, dst, size); > > > + if (IS_ERR_OR_NULL(p)) { > > > + ret =3D PTR_ERR(p); > > > > if p can really be NULL, you'd get ret =3D=3D 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 =3D strlen(p); > > > + memmove(dst, p, ret); > > > + dst[ret] =3D '\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; > > > +} > > > + > > > > [...]