From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [63.128.21.124]) by sourceware.org (Postfix) with ESMTP id 7FB4F3890405 for ; Sun, 17 Jan 2021 08:30:19 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 7FB4F3890405 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-494-pcWE-rsiO4CBR3H2ghlTOw-1; Sun, 17 Jan 2021 03:30:15 -0500 X-MC-Unique: pcWE-rsiO4CBR3H2ghlTOw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B1EC5180A092; Sun, 17 Jan 2021 08:30:14 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-112-110.ams2.redhat.com [10.36.112.110]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E278B10023B1; Sun, 17 Jan 2021 08:30:13 +0000 (UTC) From: Florian Weimer To: Andreas Fink via Libc-help Subject: Re: Hooking execve for an LD_PRELOAD library References: <1MiMEW-1lf4081KQ2-00fS4y@smtp.web.de> Date: Sun, 17 Jan 2021 09:30:10 +0100 In-Reply-To: <1MiMEW-1lf4081KQ2-00fS4y@smtp.web.de> (Andreas Fink via Libc-help's message of "Sun, 17 Jan 2021 08:07:32 +0100") Message-ID: <878s8srmnh.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Spam-Status: No, score=-6.7 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, KAM_SHORT, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-help@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-help mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 17 Jan 2021 08:30:21 -0000 * Andreas Fink via Libc-help: > Now I would like the same for execvp to happen. Reading the man page of > execvp it is mentioned that exec-family functions are just > frontends to execve, so I replaced in my executable source code the > explicit call to execve with a call to execvp. I expected that this > would just work, as execvp would in turn call execve and this would be > caught by the hook, then logged and forwarded to the real > implementation. But to my surprise no such thing happened. execvp would > run successfully, but my hook would never be called. > Why is the hook not called, what did I miss? Most internal function calls are implemented as direct function call, and it is not possible to use symbol interposition to redirect them. An exception is the malloc family of functions: Replacing malloc If you want to modify the behavior of execve, you should consider a kernel-based mechanism. This will likely make it easier to achieve correct behavior after vfork, too. Thanks, Florian -- Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn, Commercial register: Amtsgericht Muenchen, HRB 153243, Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill