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 BB533CA9EAE for ; Tue, 29 Oct 2019 18:48:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 88CF520830 for ; Tue, 29 Oct 2019 18:48:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="o51OCrY8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730531AbfJ2Ss5 (ORCPT ); Tue, 29 Oct 2019 14:48:57 -0400 Received: from mail-qt1-f195.google.com ([209.85.160.195]:33526 "EHLO mail-qt1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726861AbfJ2Ss5 (ORCPT ); Tue, 29 Oct 2019 14:48:57 -0400 Received: by mail-qt1-f195.google.com with SMTP id y39so16386848qty.0; Tue, 29 Oct 2019 11:48:56 -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; bh=WEodmOMeEny9ygdqiMPdutx+FkJbqkmU1sclkwCwk4w=; b=o51OCrY8DoAgX6WmDLslV1iyS3OX5KJMH/t71tl1Qgvj4dvhC6NHAohbNR/gEopfIq Z73Sq30X0hk9pEQ8ZelarHPwyOE2Rj1fX8/EbMEVhUXOpoo8SUqtOn6qtUsqxnP+B6Hm Tlzblkk4QGHnKy2ZL0dYr/MqEMug/XKz9vyhhBUY992tsfhNZoN8yXNMqRDUaMn35SKu R8cLqR7Vp/VR/lStjEX0TJjZkHJHnyrrwTnkqNiecrQAGIzy9lTJXXT9kqk9aP7pehJp a5rS57mQh9QYXskIgg9u6m5HcBK+r5j++HxbToyevYYSRCTXwu/IRBPo9PfDsZJOSHIF EYJQ== 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; bh=WEodmOMeEny9ygdqiMPdutx+FkJbqkmU1sclkwCwk4w=; b=GWQWGFFFskXvx94C3TuOYUc6YSRSFvFqcNZBVrLuXCEQ+gY4uIAAe3Bvq6CT4tObXT SajYSBlAQj8J0sk06pBDagHIJJHakOFPA1LwInxqpFMcNnko3jm/E0iP14bLGcTxHxbU EFVSXmbSLehbwiFdLilSiot/QyfqnguHdya6keZFmnk/XgZRBSMIah5Kvovy1CNCoOdu zqTDlzgSQA32oOiVDLwB9Awog7leByHgFDePRSOqstWNyw2DHmKZP6yJOR9touotUvxp cMoyvhOqc1cRMbv41F/J3Sa6L9i0cMsXk2ILJZePZGAjNs4FgKsj4Vm2Hez8AAaKasp6 rBxg== X-Gm-Message-State: APjAAAUybZuuPqAlzXkOmFGFd9UMCgm+4/25LKpf80GOeDuVETXknw+G izPIv6Fwx0qIY7OuM28LBz/ASiG6HhmGCsKxX9I= X-Google-Smtp-Source: APXvYqyKiUqMlNUZDWb62UhgBA1PgYyvvsfUiEFKLXRY4d4L7Vk35TTtwcXJP49nhuf0bt6nokQooKJcmto3kY0KFzQ= X-Received: by 2002:ac8:4890:: with SMTP id i16mr531582qtq.141.1572374935169; Tue, 29 Oct 2019 11:48:55 -0700 (PDT) MIME-Version: 1.0 References: <20191028141053.12267-1-ethercflow@gmail.com> In-Reply-To: <20191028141053.12267-1-ethercflow@gmail.com> From: Andrii Nakryiko Date: Tue, 29 Oct 2019 11:48:44 -0700 Message-ID: Subject: Re: [PATCH bpf-next v4] bpf: add new helper fd2path for mapping a file descriptor to a pathname To: Wenbo Zhang Cc: bpf , Yonghong Song , Daniel Borkmann , Networking Content-Type: text/plain; charset="UTF-8" Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org 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); > + return ret; > +} > + [...]