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 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 57E71C61DA4 for ; Tue, 14 Feb 2023 14:29:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1676384957; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:list-id:list-help: list-unsubscribe:list-subscribe:list-post; bh=ErJJdHsOe2XH2fbvs9MNs2aOolU46sXqyayGoKKybfU=; b=gjLWHvmQ4A3Fn7uuaSLUX5/nuu3qGJBHyPNxFnmaCGhnx1SbxszGd6YYUxY9qtr2RjLK2u nVC2ef1dIgSRucAuEvZwswbhlUNfYgVLodspKT3VFGDaC1DDmCVrkLlBnB2tS2iH+SQAMP lltyl6uQlck81H2GY3f7M7DRaEwniCc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-612-OWiy2Oy0NdKateOoeagQ7Q-1; Tue, 14 Feb 2023 09:29:14 -0500 X-MC-Unique: OWiy2Oy0NdKateOoeagQ7Q-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 989D9971081; Tue, 14 Feb 2023 14:29:12 +0000 (UTC) Received: from mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com [10.30.29.100]) by smtp.corp.redhat.com (Postfix) with ESMTP id D564B492B03; Tue, 14 Feb 2023 14:29:09 +0000 (UTC) Received: from mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (localhost [IPv6:::1]) by mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (Postfix) with ESMTP id AB915194658C; Tue, 14 Feb 2023 14:29:04 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) by mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (Postfix) with ESMTP id E278B1946588 for ; Tue, 14 Feb 2023 14:29:03 +0000 (UTC) Received: by smtp.corp.redhat.com (Postfix) id CE5C91415108; Tue, 14 Feb 2023 14:29:03 +0000 (UTC) Received: from x2.localnet (unknown [10.22.9.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A8A94140EBF6; Tue, 14 Feb 2023 14:29:03 +0000 (UTC) From: Steve Grubb To: linux-audit@redhat.com Subject: Re: Clarification Around File System Auditing Date: Tue, 14 Feb 2023 09:29:03 -0500 Message-ID: <4814542.31r3eYUQgx@x2> Organization: Red Hat In-Reply-To: References: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 X-BeenThere: linux-audit@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux Audit Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Amjad Gabbar Errors-To: linux-audit-bounces@redhat.com Sender: "Linux-audit" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Hello, On Monday, February 13, 2023 4:24:02 PM EST Amjad Gabbar wrote: > I wanted some help in better understanding the workflow of file system > auditing(watch rules) vs Syscall Auditing(syscall rules). I know in general > file system auditing does not have the same performance impact as syscall > auditing, even though both make use of syscall exits for their evaluation. > > > From the manpage - "Unlike most syscall auditing rules, watches do not > impact performance based on the number of rules sent to the kernel." > > From a previous thread, I found this excerpt regarding file watch rules vs > sycall rules - > > "The reason it doesn't have performance impact like normal syscall rules is > because it gets moved to a list that is not evaluated every syscall. A > normal syscall rule will get evaluated for every syscall because it has to > see if the syscall number is of interest and then it checks the next > rule." > > Based on this I had a couple of questions: > > For normal syscall rules, the evaluation happens as __audit_syscall_exit > > calls audit_filter_syscall > (https://elixir.bootlin.com/linux/v6.1.10/source/kernel/auditsc.c#L841) > > Here, we check if the syscall is of interest or not in the audit_in_mask > function. > Only if the syscall is of interest do we proceed with examining the task > and return on the first rule match. > > 1. What is the process or code path for watch rules? audit_filter_syscall > is > called for watch rules as well. Then how is it that these are not called > for every syscall? Could you point me to the code where the evaluation > happens only once? There is a file, kernel/audit_watch.c, that implements the interface between audit and fsnotify. You would want to learn how fsnotify works to understand how it avoids the syscall filter. > 2. Also, do file watches only involve the open system call family (open, > openat etc). The man page implies the same, so just wanted to confirm. > > I assume -w /etc -p wa is the same as -a always,exit -S open -S openat -F > dir=/etc? It depends on the flag passed for perm as to what syscall it wants. See: include/asm-generic/audit_*.h -Steve -- Linux-audit mailing list Linux-audit@redhat.com https://listman.redhat.com/mailman/listinfo/linux-audit