From patchwork Wed Dec 5 08:35:35 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Aneesh Kumar K.V" X-Patchwork-Id: 203801 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 34AB62C00D0 for ; Wed, 5 Dec 2012 19:36:05 +1100 (EST) Received: from localhost ([::1]:37360 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TgASZ-0000YF-R1 for incoming@patchwork.ozlabs.org; Wed, 05 Dec 2012 03:36:03 -0500 Received: from eggs.gnu.org ([208.118.235.92]:48046) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TgASQ-0000Xq-5l for qemu-devel@nongnu.org; Wed, 05 Dec 2012 03:35:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TgASH-0001ai-GM for qemu-devel@nongnu.org; Wed, 05 Dec 2012 03:35:54 -0500 Received: from e23smtp03.au.ibm.com ([202.81.31.145]:53518) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TgASG-0001a9-MY for qemu-devel@nongnu.org; Wed, 05 Dec 2012 03:35:45 -0500 Received: from /spool/local by e23smtp03.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Wed, 5 Dec 2012 18:31:48 +1000 Received: from d23relay04.au.ibm.com (d23relay04.au.ibm.com [9.190.234.120]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id 836BD2CE804B; Wed, 5 Dec 2012 19:35:38 +1100 (EST) Received: from d23av01.au.ibm.com (d23av01.au.ibm.com [9.190.234.96]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id qB58Ong258327262; Wed, 5 Dec 2012 19:24:50 +1100 Received: from d23av01.au.ibm.com (loopback [127.0.0.1]) by d23av01.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id qB58ZbCw002249; Wed, 5 Dec 2012 19:35:37 +1100 Received: from skywalker.linux.vnet.ibm.com (skywalker.in.ibm.com [9.124.35.157]) by d23av01.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id qB58ZZSl002208; Wed, 5 Dec 2012 19:35:36 +1100 From: "Aneesh Kumar K.V" To: Paolo Bonzini , "M. Mohan Kumar" In-Reply-To: <87y5hdejes.fsf@linux.vnet.ibm.com> References: <1349868762-10021-1-git-send-email-pbonzini@redhat.com> <50759EEC.8070308@weilnetz.de> <50759F9E.3060800@redhat.com> <5075A0FF.3080904@weilnetz.de> <5075A420.10003@redhat.com> <5075A843.8020107@weilnetz.de> <5075A966.3090708@weilnetz.de> <871uh5tqr7.fsf@explorer.in.ibm.com> <5076BACC.7030309@redhat.com> <87y5hdejes.fsf@linux.vnet.ibm.com> User-Agent: Notmuch/0.14+97~g3977b25 (http://notmuchmail.org) Emacs/24.3.50.1 (x86_64-unknown-linux-gnu) Date: Wed, 05 Dec 2012 14:05:35 +0530 Message-ID: <87obi8ew14.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12120508-6102-0000-0000-000002AB492E X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.4.x-2.6.x [generic] X-Received-From: 202.81.31.145 Cc: qemu-trivial@nongnu.org, Stefan Weil , qemu-devel@nongnu.org Subject: Re: [Qemu-devel] [PATCH] virtfs-proxy-helper: check return code of setfsgid/setfsuid X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Hi, I have tested the below patch. Currently i don't have a signed-off-by on the patch. One change noted by mohan which I incorporated in the patch is we need to call setresgid before calling setresuid. If you are ok with this change I can send it upstream. commit d11bb5bb31a68e3eefb4e592161978dba29137f5 Author: Paolo Bonzini Date: Thu Oct 11 14:20:23 2012 +0200 virtfs-proxy-helper: use setresuid and setresgid The setfsuid and setfsgid system calls are obscure and they complicate the error checking (that glibc's warn_unused_result "feature" forces us to do). Switch to the standard setresuid and setresgid functions. Signed-off-by: Aneesh Kumar K.V diff --git a/fsdev/virtfs-proxy-helper.c b/fsdev/virtfs-proxy-helper.c index f9a8270..df2a939 100644 --- a/fsdev/virtfs-proxy-helper.c +++ b/fsdev/virtfs-proxy-helper.c @@ -272,31 +272,76 @@ static int send_status(int sockfd, struct iovec *iovec, int status) /* * from man 7 capabilities, section * Effect of User ID Changes on Capabilities: - * 4. If the file system user ID is changed from 0 to nonzero (see setfsuid(2)) - * then the following capabilities are cleared from the effective set: - * CAP_CHOWN, CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH, CAP_FOWNER, CAP_FSETID, - * CAP_LINUX_IMMUTABLE (since Linux 2.2.30), CAP_MAC_OVERRIDE, and CAP_MKNOD - * (since Linux 2.2.30). If the file system UID is changed from nonzero to 0, - * then any of these capabilities that are enabled in the permitted set - * are enabled in the effective set. + * If the effective user ID is changed from nonzero to 0, then the permitted + * set is copied to the effective set. If the effective user ID is changed + * from 0 to nonzero, then all capabilities are are cleared from the effective + * set. + * + * The setfsuid/setfsgid man pages warn that changing the effective user ID may + * expose the program to unwanted signals, but this is not true anymore: for an + * unprivileged (without CAP_KILL) program to send a signal, the real or + * effective user ID of the sending process must equal the real or saved user + * ID of the target process. Even when dropping privileges, it is enough to + * keep the saved UID to a "privileged" value and virtfs-proxy-helper won't + * be exposed to signals. So just use setresuid/setresgid. */ -static int setfsugid(int uid, int gid) +static int setugid(int uid, int gid, int *suid, int *sgid) { + int retval; + /* - * We still need DAC_OVERRIDE because we don't change + * We still need DAC_OVERRIDE because we don't change * supplementary group ids, and hence may be subjected DAC rules */ cap_value_t cap_list[] = { CAP_DAC_OVERRIDE, }; - setfsgid(gid); - setfsuid(uid); + *suid = geteuid(); + *sgid = getegid(); + + if (setresgid(-1, gid, *sgid) == -1) { + retval = -errno; + goto err_out; + } + + if (setresuid(-1, uid, *suid) == -1) { + retval = -errno; + goto err_sgid; + } if (uid != 0 || gid != 0) { - return do_cap_set(cap_list, ARRAY_SIZE(cap_list), 0); + if (do_cap_set(cap_list, ARRAY_SIZE(cap_list), 0) < 0) { + retval = -errno; + goto err_suid; + } } return 0; + +err_suid: + if (setresuid(-1, *suid, *suid) == -1) { + abort(); + } +err_sgid: + if (setresgid(-1, *sgid, *sgid) == -1) { + abort(); + } +err_out: + return retval; +} + +/* + * This is used to reset the ugid back with the saved values + * There is nothing much we can do checking error values here. + */ +static void resetugid(int suid, int sgid) +{ + if (setresgid(-1, sgid, sgid) == -1) { + abort(); + } + if (setresuid(-1, suid, suid) == -1) { + abort(); + } } /* @@ -578,18 +623,15 @@ static int do_create_others(int type, struct iovec *iovec) v9fs_string_init(&path); v9fs_string_init(&oldpath); - cur_uid = geteuid(); - cur_gid = getegid(); retval = proxy_unmarshal(iovec, offset, "dd", &uid, &gid); if (retval < 0) { return retval; } offset += retval; - retval = setfsugid(uid, gid); + retval = setugid(uid, gid, &cur_uid, &cur_gid); if (retval < 0) { - retval = -errno; - goto err_out; + goto unmarshal_err_out; } switch (type) { case T_MKNOD: @@ -619,9 +661,10 @@ static int do_create_others(int type, struct iovec *iovec) } err_out: + resetugid(cur_uid, cur_gid); +unmarshal_err_out: v9fs_string_free(&path); v9fs_string_free(&oldpath); - setfsugid(cur_uid, cur_gid); return retval; } @@ -641,24 +684,16 @@ static int do_create(struct iovec *iovec) if (ret < 0) { goto unmarshal_err_out; } - cur_uid = geteuid(); - cur_gid = getegid(); - ret = setfsugid(uid, gid); + ret = setugid(uid, gid, &cur_uid, &cur_gid); if (ret < 0) { - /* - * On failure reset back to the - * old uid/gid - */ - ret = -errno; - goto err_out; + goto unmarshal_err_out; } ret = open(path.data, flags, mode); if (ret < 0) { ret = -errno; } -err_out: - setfsugid(cur_uid, cur_gid); + resetugid(cur_uid, cur_gid); unmarshal_err_out: v9fs_string_free(&path); return ret;