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 5944FC636D6 for ; Fri, 17 Feb 2023 21:50:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1676670623; 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=CW4KX0/4eiZ6kaufyMkdQgxpUKZFkjNSO3ns8ppkk60=; b=Eb2LwWib38Aggq2ydFEI5dKv/7deMtI7uEfOYPZUIR3rTZGX9kYQEulYqSVyFbVNgtTzfi fAFpcPwBTQMprjRQtWSUZ/4S2M10kF+3oFL9fQ3RKE7nXIFJpdXjiEMYT78GXHnxCSegN1 Cb4lizA2vSG9G9UCQiwsk3rXREQEnbY= 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-634-bqcrFse3OvKRxLz629DDeg-1; Fri, 17 Feb 2023 16:50:20 -0500 X-MC-Unique: bqcrFse3OvKRxLz629DDeg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CFCD8811E6E; Fri, 17 Feb 2023 21:50:18 +0000 (UTC) Received: from mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (unknown [10.30.29.100]) by smtp.corp.redhat.com (Postfix) with ESMTP id 33A44C15BA0; Fri, 17 Feb 2023 21:50:17 +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 09C491946589; Fri, 17 Feb 2023 21:50:17 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) by mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (Postfix) with ESMTP id C0ED4194658D for ; Fri, 17 Feb 2023 21:50:16 +0000 (UTC) Received: by smtp.corp.redhat.com (Postfix) id 7D36D2026D68; Fri, 17 Feb 2023 21:50:16 +0000 (UTC) Received: from x2.localnet (unknown [10.22.33.88]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 449912026D4B; Fri, 17 Feb 2023 21:50:16 +0000 (UTC) From: Steve Grubb To: Amjad Gabbar Subject: Re: Clarification Around File System Auditing Date: Fri, 17 Feb 2023 16:50:15 -0500 Message-ID: <2289859.ElGaqSPkdT@x2> Organization: Red Hat In-Reply-To: References: <4814542.31r3eYUQgx@x2> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 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: linux-audit@redhat.com Errors-To: linux-audit-bounces@redhat.com Sender: "Linux-audit" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Hello, On Tuesday, February 14, 2023 3:55:58 PM EST Amjad Gabbar wrote: > Thanks for the reply. > I was trying to evaluate the same via Flamegraphs and what I noticed was > that : > > 1. Despite deleting all rules (auditctl -D), there were still calls to > audit_filter_syscall() on each syscall. I assume this is because syscall > auditing is enabled and despite no rules, there still will be some > performance impact and calls to syscall filtering functions on each > syscall. Yes. > 2. For a single watch rule as well without any syscall rules, I could see > calls to audit_filter_syscall() followed by audit_filter_rules() for > unrelated syscalls such as futex() and recvmsg() - not present in > include/asm-generic/audit_*.h > Why would these functions be called for a single watch rule for syscalls > unrelated to the permissions? If auditing is enabled, it will go into the syscall filter for *any* syscall. It will go into __audit_syscall_exit for every syscall. If there is an audit context, it will go into audit_filter_syscall. The documentation in the comments above these functions is informative. My guess is that this code path might benefit from adding a list_empty check. A long time ago, I think we kept a variable that denoted if there were any rules and short-circuited if none. -Steve > On Tue, Feb 14, 2023 at 8:29 AM Steve Grubb wrote: > > 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