From patchwork Mon Jun 8 09:31:11 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Max Reitz X-Patchwork-Id: 281187 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=-6.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS autolearn=ham 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 AC5B6C433E0 for ; Mon, 8 Jun 2020 09:32:34 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7104F206A4 for ; Mon, 8 Jun 2020 09:32:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="YPKqKnew" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7104F206A4 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:34284 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jiE8u-00036I-Ka for qemu-devel@archiver.kernel.org; Mon, 08 Jun 2020 05:32:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49068) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jiE7p-00029U-TT for qemu-devel@nongnu.org; Mon, 08 Jun 2020 05:31:25 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:49046 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jiE7o-0000oX-Kk for qemu-devel@nongnu.org; Mon, 08 Jun 2020 05:31:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591608682; 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; bh=Ojp+Pake/wRUXE1XQtJ+m2d5sFMSvo7+5nJ+v9MXU+0=; b=YPKqKnew5EGN2PclAjHQQaNbdZZZLd0pc3tjm3KqBo76+3yVKFV8lu6xLAg7H8BpGY0ItD bgdx/ro9TvA504k1nJYCR1Gmr5vB7IWH61o+bo3dZ4iAqbwgCuW0hkBDe9AlRgQuAI50Sz qRwg/yvPEbGhqcE4j8hwDNvJh8y2mVY= 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-454-JbP-naJJMAyiOPJWWcNh8g-1; Mon, 08 Jun 2020 05:31:20 -0400 X-MC-Unique: JbP-naJJMAyiOPJWWcNh8g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 064BC107ACCA; Mon, 8 Jun 2020 09:31:20 +0000 (UTC) Received: from localhost (ovpn-113-71.ams2.redhat.com [10.36.113.71]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9B4C85C1B2; Mon, 8 Jun 2020 09:31:13 +0000 (UTC) From: Max Reitz To: qemu-devel@nongnu.org Subject: [PATCH] virtiofsd: Whitelist fchmod Date: Mon, 8 Jun 2020 11:31:11 +0200 Message-Id: <20200608093111.14942-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=205.139.110.120; envelope-from=mreitz@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/08 01:05:50 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: virtio-fs@redhat.com, Stefan Hajnoczi , qemu-stable@nongnu.org, "Dr . David Alan Gilbert" , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" lo_setattr() invokes fchmod() in a rarely used code path, so it should be whitelisted or virtiofsd will crash with EBADSYS. Said code path can be triggered for example as follows: On the host, in the shared directory, create a file with the sticky bit set and a security.capability xattr: (1) # touch foo (2) # chmod u+s foo (3) # setcap '' foo Then in the guest let some process truncate that file after it has dropped all of its capabilities (at least CAP_FSETID): int main(int argc, char *argv[]) { capng_setpid(getpid()); capng_clear(CAPNG_SELECT_BOTH); capng_updatev(CAPNG_ADD, CAPNG_PERMITTED | CAPNG_EFFECTIVE, 0); capng_apply(CAPNG_SELECT_BOTH); ftruncate(open(argv[1], O_RDWR), 0); } This will cause the guest kernel to drop the sticky bit (i.e. perform a mode change) as part of the truncate (where FATTR_FH is set), and that will cause virtiofsd to invoke fchmod() instead of fchmodat(). (A similar configuration exists further below with futimens() vs. utimensat(), but the former is not a syscall but just a wrapper for the latter, so no further whitelisting is required.) Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1842667 Reported-by: Qian Cai Cc: qemu-stable@nongnu.org Signed-off-by: Max Reitz --- tools/virtiofsd/seccomp.c | 1 + 1 file changed, 1 insertion(+) diff --git a/tools/virtiofsd/seccomp.c b/tools/virtiofsd/seccomp.c index bd9e7b083c..3b1522acdd 100644 --- a/tools/virtiofsd/seccomp.c +++ b/tools/virtiofsd/seccomp.c @@ -42,6 +42,7 @@ static const int syscall_whitelist[] = { SCMP_SYS(exit_group), SCMP_SYS(fallocate), SCMP_SYS(fchdir), + SCMP_SYS(fchmod), SCMP_SYS(fchmodat), SCMP_SYS(fchownat), SCMP_SYS(fcntl),