From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by passt.top (Postfix) with ESMTP id B71A45A005E for ; Thu, 17 Nov 2022 16:49:36 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668700175; h=from:from: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; bh=jxA5mV/ZAm9DCYhHY9xevzF8IF+giMKS5N6RT4wcVE0=; b=Ee4HY+tGKZfXaoysAJlbmGFqu5I6AmGs3Q7RoZBNlo3MzSySOr5eo5rwAFMnuO0sq+Ukpr t/0yy3I0GLtCQCWYlxVVE2HHqdblTflEsbHLmW8fR+N3o5m8E8y0N/35MAyMiaLRutS8Xd QfJ6Dize2YCcSSN/USmmGD3Qmgfm/xo= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-241-6X97PMtTPoK8gH66AhQkcg-1; Thu, 17 Nov 2022 10:49:34 -0500 X-MC-Unique: 6X97PMtTPoK8gH66AhQkcg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id F126E1C004F9 for ; Thu, 17 Nov 2022 15:49:33 +0000 (UTC) Received: from maya.cloud.tilaa.com (ovpn-208-8.brq.redhat.com [10.40.208.8]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C53F82166B29; Thu, 17 Nov 2022 15:49:33 +0000 (UTC) Date: Thu, 17 Nov 2022 16:49:31 +0100 From: Stefano Brivio To: "Richard W.M. Jones" Subject: Re: [PATCH v2 3/5] passt, tap: Add --fd option Message-ID: <20221117164931.5585f60f@elisabeth> In-Reply-To: <20221117153306.GF7636@redhat.com> References: <20221117122614.1269214-4-rjones@redhat.com> <20221117152640.2535159-1-sbrivio@redhat.com> <20221117153306.GF7636@redhat.com> Organization: Red Hat MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: CY6MWIQ7YFAWBHFDW4VDEZ4TLBI3ZJ4E X-Message-ID-Hash: CY6MWIQ7YFAWBHFDW4VDEZ4TLBI3ZJ4E X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top X-Mailman-Version: 3.3.3 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Thu, 17 Nov 2022 15:33:06 +0000 "Richard W.M. Jones" wrote: > On Thu, Nov 17, 2022 at 04:26:40PM +0100, Stefano Brivio wrote: > > From: "Richard W.M. Jones" > > > > This passes a fully connected stream socket to passt. > > > > Signed-off-by: Richard W.M. Jones > > [sbrivio: reuse fd_tap instead of adding a new descriptor, > > imply --one-off on --fd, add to optstring and usage()] > > Signed-off-by: Stefano Brivio > > --- > > v2: > > - reuse fd_tap, we don't need a separate file descriptor > > - add F to optstring and usage(), for both passt and pasta > > - imply --one-off, we can't do much once the socket is closed > > > > With this, the trick from 5/5 goes a bit further: passt reads > > from the file descriptor passed by the wrapper. > > Thanks for the v2 .. I'll add it to my series and play with it. > > > However, we get EPOLLRDHUP right away, from the close() on > > one end of the socket pair I guess. Should we just ignore > > all EPOLLRDHUP events, just the first one...? > > Does it see the event out-of-band or does it get an in-band > read(2) == 0 after finishing reading the data? Out-of-band, so to speak: we won't even recv() if we get EPOLLRDHUP (that's handled in tap_handler()). If I do this on top of this patch: --- a/tap.c +++ b/tap.c @@ -1073,7 +1073,7 @@ void tap_sock_init(struct ctx *c) struct epoll_event ev = { 0 }; ev.data.fd = c->fd_tap; - ev.events = EPOLLIN | EPOLLET | EPOLLRDHUP; + ev.events = EPOLLIN | EPOLLET; Then it gets those four bytes: [pid 2538704] epoll_wait(5, 0x7ffedc4a6320, 8, 1000) = 1 [pid 2538704] recvfrom(4, 0x560797677000, 8323069, MSG_DONTWAIT, NULL, NULL) = 4 [pid 2538704] epoll_wait(5, [], 8, 1000) = 0 [pid 2538704] epoll_wait(5, 0x7ffedc4a6320, 8, 1000) = -1 EINTR (Interrupted system call) and does nothing with them, as expected. Two epoll_wait() calls later, the syscall is interrupted, I'm not sure why and how we should react (in main(), passt.c) in that case. > Ideally what should happen is that passt reads and parses all or as > much of the data as it can, and then it responds to the closed socket > by exiting. The reason for this is so that we have as much > opportunity as possible to break the parser and crash passt. So probably ignoring EPOLLRDHUP is safe. If the socket is closed we should get EPOLLHUP. > If passt was exiting before fully reading/parsing everything that it > could, then we wouldn't be fuzzing the parser as deeply as we can. We would process a EPOLLRDHUP or EPOLLHUP before doing anything, yes (also in tap_handler()). But if we get a EPOLLIN event first, then it's fine, we'll read everything. > Note that the fuzzer will (quite routinely and normally) create test > cases which are total nonsense, eg. packets with incorrect length > field, truncated final packet, etc. Yes yes, I can imagine. :) -- Stefano