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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A0ABCC43603 for ; Tue, 17 Dec 2019 19:39:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 786D02146E for ; Tue, 17 Dec 2019 19:39:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727773AbfLQTje (ORCPT ); Tue, 17 Dec 2019 14:39:34 -0500 Received: from www62.your-server.de ([213.133.104.62]:50978 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726612AbfLQTje (ORCPT ); Tue, 17 Dec 2019 14:39:34 -0500 Received: from sslproxy02.your-server.de ([78.47.166.47]) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1ihIgs-00037v-NF; Tue, 17 Dec 2019 20:39:30 +0100 Received: from [178.197.249.31] (helo=pc-9.home) by sslproxy02.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1ihIgs-000HxU-Dm; Tue, 17 Dec 2019 20:39:30 +0100 Subject: Re: [PATCH bpf-next v13 1/2] bpf: add new helper get_fd_path for mapping a file descriptor to a pathname To: Yonghong Song , Wenbo Zhang , "bpf@vger.kernel.org" Cc: "ast@kernel.org" , "bgregg@netflix.com" , "andrii.nakryiko@gmail.com" , "netdev@vger.kernel.org" References: <8f6b8979fb64bedf5cb406ba29146c5fa2539267.1576575253.git.ethercflow@gmail.com> From: Daniel Borkmann Message-ID: Date: Tue, 17 Dec 2019 20:39:29 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.101.4/25666/Tue Dec 17 10:54:52 2019) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 12/17/19 5:29 PM, Yonghong Song wrote: > On 12/17/19 1:47 AM, Wenbo Zhang wrote: [...] >> + * On failure, it is filled with zeroes. [...] >> */ >> #define __BPF_FUNC_MAPPER(FN) \ >> FN(unspec), \ >> @@ -2938,7 +2964,8 @@ union bpf_attr { >> FN(probe_read_user), \ >> FN(probe_read_kernel), \ >> FN(probe_read_user_str), \ >> - FN(probe_read_kernel_str), >> + FN(probe_read_kernel_str), \ >> + FN(get_fd_path), >> >> /* 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 e5ef4ae9edb5..43a6aa6ad967 100644 >> --- a/kernel/trace/bpf_trace.c >> +++ b/kernel/trace/bpf_trace.c >> @@ -762,6 +762,71 @@ static const struct bpf_func_proto bpf_send_signal_proto = { >> .arg1_type = ARG_ANYTHING, >> }; >> >> +BPF_CALL_3(bpf_get_fd_path, char *, dst, u32, size, int, fd) >> +{ >> + int ret = -EBADF; >> + struct file *f; >> + char *p; >> + >> + /* Ensure we're in user context which is safe for the helper to >> + * run. This helper has no business in a kthread. >> + */ >> + if (unlikely(in_interrupt() || >> + current->flags & (PF_KTHREAD | PF_EXITING))) { >> + ret = -EPERM; >> + goto error; >> + } >> + >> + /* Use fget_raw instead of fget to support O_PATH, and it doesn't >> + * have any sleepable code, so it's ok to be here. >> + */ >> + f = fget_raw(fd); >> + if (!f) >> + goto error; >> + >> + /* For unmountable pseudo filesystem, it seems to have no meaning >> + * to get their fake paths as they don't have path, and to be no >> + * way to validate this function pointer can be always safe to call >> + * in the current context. >> + */ >> + if (f->f_path.dentry->d_op && f->f_path.dentry->d_op->d_dname) { >> + ret = -EINVAL; >> + fput(f); >> + goto error; >> + } >> + >> + /* After filter unmountable pseudo filesytem, d_path won't call >> + * dentry->d_op->d_name(), the normally path doesn't have any >> + * sleepable code, and despite it uses the current macro to get >> + * fs_struct (current->fs), we've already ensured we're in user >> + * context, so it's ok to be here. >> + */ >> + p = d_path(&f->f_path, dst, size); >> + if (IS_ERR(p)) { >> + ret = PTR_ERR(p); >> + fput(f); >> + goto error; >> + } >> + >> + ret = strlen(p) + 1; >> + memmove(dst, p, ret); >> + fput(f); >> + return ret; >> + >> +error: >> + memset(dst, '0', size); You fill it with 0x30's ... >> + return ret; >> +}