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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 B9B08C282C3 for ; Thu, 24 Jan 2019 19:57:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 88C5B21726 for ; Thu, 24 Jan 2019 19:57:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548359866; bh=mv9SVDBEnZXZxobwT4Cpu2wS+OzU/G0wETOEeo38ZDA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=wAVXxworkUr4msDVwmbjDa0ETTUu662l7cUvMf8bLwUclFNggtA5tw4v2PGzU88iE a3dr6juQdFAh/dUkVP4k5B473eeudV6CjlGgbCnuyvSIS9uxhhYYHBv8DwIdeAsvXq seXSFeEFjGb9tdEUr++JC4f0hg+Fm3OB/2IadXZs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729789AbfAXTfA (ORCPT ); Thu, 24 Jan 2019 14:35:00 -0500 Received: from mail.kernel.org ([198.145.29.99]:34808 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731468AbfAXTe6 (ORCPT ); Thu, 24 Jan 2019 14:34:58 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 14397218FC; Thu, 24 Jan 2019 19:34:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548358497; bh=mv9SVDBEnZXZxobwT4Cpu2wS+OzU/G0wETOEeo38ZDA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=T4EhKNcfrmcmPJhJ1kzZY9EBVcb/HnmSv3pkD48cvrRam3Ds/Jd7hglhUtU+Uir9k 4n3bZ89raWus6Ze8MftL8UXJ35ki6njDPhh0hQhVw1BLu4qBPlkexALyakJOQOxbgj KtiI24XJG2aM8g8QlOTLWbXjgxd7cRft8RRGI2UE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Daniel T. Lee" , Daniel Borkmann , Sasha Levin Subject: [PATCH 4.19 030/106] samples: bpf: fix: error handling regarding kprobe_events Date: Thu, 24 Jan 2019 20:19:47 +0100 Message-Id: <20190124190208.284098390@linuxfoundation.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190124190206.342411005@linuxfoundation.org> References: <20190124190206.342411005@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 4.19-stable review patch. If anyone has any objections, please let me know. ------------------ [ Upstream commit 5a863813216ce79e16a8c1503b2543c528b778b6 ] Currently, kprobe_events failure won't be handled properly. Due to calling system() indirectly to write to kprobe_events, it can't be identified whether an error is derived from kprobe or system. // buf = "echo '%c:%s %s' >> /s/k/d/t/kprobe_events" err = system(buf); if (err < 0) { printf("failed to create kprobe .."); return -1; } For example, running ./tracex7 sample in ext4 partition, "echo p:open_ctree open_ctree >> /s/k/d/t/kprobe_events" gets 256 error code system() failure. => The error comes from kprobe, but it's not handled correctly. According to man of system(3), it's return value just passes the termination status of the child shell rather than treating the error as -1. (don't care success) Which means, currently it's not working as desired. (According to the upper code snippet) ex) running ./tracex7 with ext4 env. # Current Output sh: echo: I/O error failed to open event open_ctree # Desired Output failed to create kprobe 'open_ctree' error 'No such file or directory' The problem is, error can't be verified whether from child ps or system. But using write() directly can verify the command failure, and it will treat all error as -1. So I suggest using write() directly to 'kprobe_events' rather than calling system(). Signed-off-by: Daniel T. Lee Signed-off-by: Daniel Borkmann Signed-off-by: Sasha Levin --- samples/bpf/bpf_load.c | 33 ++++++++++++++++++++++++--------- 1 file changed, 24 insertions(+), 9 deletions(-) diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c index 904e775d1a44..cf40a8284a38 100644 --- a/samples/bpf/bpf_load.c +++ b/samples/bpf/bpf_load.c @@ -55,6 +55,23 @@ static int populate_prog_array(const char *event, int prog_fd) return 0; } +static int write_kprobe_events(const char *val) +{ + int fd, ret, flags; + + if ((val != NULL) && (val[0] == '\0')) + flags = O_WRONLY | O_TRUNC; + else + flags = O_WRONLY | O_APPEND; + + fd = open("/sys/kernel/debug/tracing/kprobe_events", flags); + + ret = write(fd, val, strlen(val)); + close(fd); + + return ret; +} + static int load_and_attach(const char *event, struct bpf_insn *prog, int size) { bool is_socket = strncmp(event, "socket", 6) == 0; @@ -166,10 +183,9 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size) #ifdef __x86_64__ if (strncmp(event, "sys_", 4) == 0) { - snprintf(buf, sizeof(buf), - "echo '%c:__x64_%s __x64_%s' >> /sys/kernel/debug/tracing/kprobe_events", - is_kprobe ? 'p' : 'r', event, event); - err = system(buf); + snprintf(buf, sizeof(buf), "%c:__x64_%s __x64_%s", + is_kprobe ? 'p' : 'r', event, event); + err = write_kprobe_events(buf); if (err >= 0) { need_normal_check = false; event_prefix = "__x64_"; @@ -177,10 +193,9 @@ static int load_and_attach(const char *event, struct bpf_insn *prog, int size) } #endif if (need_normal_check) { - snprintf(buf, sizeof(buf), - "echo '%c:%s %s' >> /sys/kernel/debug/tracing/kprobe_events", - is_kprobe ? 'p' : 'r', event, event); - err = system(buf); + snprintf(buf, sizeof(buf), "%c:%s %s", + is_kprobe ? 'p' : 'r', event, event); + err = write_kprobe_events(buf); if (err < 0) { printf("failed to create kprobe '%s' error '%s'\n", event, strerror(errno)); @@ -520,7 +535,7 @@ static int do_load_bpf_file(const char *path, fixup_map_cb fixup_map) return 1; /* clear all kprobes */ - i = system("echo \"\" > /sys/kernel/debug/tracing/kprobe_events"); + i = write_kprobe_events(""); /* scan over all elf sections to get license and map info */ for (i = 1; i < ehdr.e_shnum; i++) { -- 2.19.1