From patchwork Tue Dec 21 02:17:44 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 12688871 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 290DDC433F5 for ; Tue, 21 Dec 2021 02:18:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232354AbhLUCSI (ORCPT ); Mon, 20 Dec 2021 21:18:08 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:32561 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230060AbhLUCSH (ORCPT ); Mon, 20 Dec 2021 21:18:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1640053086; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=92jGNB0gro1jXL9B2iwhe5DeDQMLoKCOk9yvZGwt2nw=; b=ebjyrqKsvlqP5qqfKXdxS4SyT8TTyBEJqGQSLxu3aadOj/BfA/4AQTspSeA8WsBH4N/KSl 3bmmQRPPmwoNFMBI4QbvdVFFQBn9t/b/A034LqKWy/5VYL1tTXR7Pr5hHWe0aH7UZpWm0G hTmT53dgQsfRECJqsx2kFWAeKzkbHGQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-542-rzYvQeGTNmyk3u_L7d7G2A-1; Mon, 20 Dec 2021 21:18:01 -0500 X-MC-Unique: rzYvQeGTNmyk3u_L7d7G2A-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B0DC2801B0B; Tue, 21 Dec 2021 02:17:59 +0000 (UTC) Received: from llong.com (unknown [10.22.16.152]) by smtp.corp.redhat.com (Postfix) with ESMTP id B804E2B46A; Tue, 21 Dec 2021 02:17:55 +0000 (UTC) From: Waiman Long To: Alexander Viro , Eric Biederman , Kees Cook Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Laurent Vivier , YunQiang Su , Helge Deller , Waiman Long Subject: [PATCH] exec: Make suid_dumpable apply to SUID/SGID binaries irrespective of invoking users Date: Mon, 20 Dec 2021 21:17:44 -0500 Message-Id: <20211221021744.864115-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org The begin_new_exec() function checks for SUID or SGID binaries by comparing effective uid and gid against real uid and gid and using the suid_dumpable sysctl parameter setting only if either one of them differs. In the special case that the uid and/or gid of the SUID/SGID binaries matches the id's of the user invoking it, the suid_dumpable is not used and SUID_DUMP_USER will be used instead. The documentation for the suid_dumpable sysctl parameter does not include that exception and so this will be an undocumented behavior. Eliminate this undocumented behavior by adding a flag in the linux_binprm structure to designate a SUID/SGID binary and use it for determining if the suid_dumpable setting should be applied or not. Signed-off-by: Waiman Long --- fs/exec.c | 6 +++--- include/linux/binfmts.h | 5 ++++- 2 files changed, 7 insertions(+), 4 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 537d92c41105..60e02e678fb6 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1344,9 +1344,7 @@ int begin_new_exec(struct linux_binprm * bprm) * is wrong, but userspace depends on it. This should be testing * bprm->secureexec instead. */ - if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP || - !(uid_eq(current_euid(), current_uid()) && - gid_eq(current_egid(), current_gid()))) + if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP || bprm->is_sugid) set_dumpable(current->mm, suid_dumpable); else set_dumpable(current->mm, SUID_DUMP_USER); @@ -1619,11 +1617,13 @@ static void bprm_fill_uid(struct linux_binprm *bprm, struct file *file) if (mode & S_ISUID) { bprm->per_clear |= PER_CLEAR_ON_SETID; bprm->cred->euid = uid; + bprm->is_sugid = 1; } if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) { bprm->per_clear |= PER_CLEAR_ON_SETID; bprm->cred->egid = gid; + bprm->is_sugid = 1; } } diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index 049cf9421d83..6d9893c59085 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -41,7 +41,10 @@ struct linux_binprm { * Set when errors can no longer be returned to the * original userspace. */ - point_of_no_return:1; + point_of_no_return:1, + + /* Is a SUID or SGID binary? */ + is_sugid:1; #ifdef __alpha__ unsigned int taso:1; #endif