From nobody Wed Sep 3 01:50:28 2025 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 60039ECAAD5 for ; Fri, 2 Sep 2022 12:33:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236832AbiIBMdX (ORCPT ); Fri, 2 Sep 2022 08:33:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47798 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236255AbiIBMcI (ORCPT ); Fri, 2 Sep 2022 08:32:08 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63993E1A87; Fri, 2 Sep 2022 05:27:03 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 03D7AB82A93; Fri, 2 Sep 2022 12:26:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C714C433C1; Fri, 2 Sep 2022 12:26:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1662121601; bh=nN8ADwqc5PZvKklE1YnMtGZ5CSJV3QwI3GVA9DAi9VU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZnoWNNfcntcwFYqYOCLJc1oySTMNh3Ctxq8Nyi3F5ntrP47Npu7ixyXuB6a/lsL0N du2KoEl2jaRmTHNOLtMntWCw3/KRcQCauK/t5ZnnhKpptQyEsJHHBvpg0aqWVYocPf mf6lUkUWvR6yIjyTljRJKB/TMFydqBk4YpO3RzVk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Brian Foster , Gerald Schaefer , Heiko Carstens , Vasily Gorbik Subject: [PATCH 4.19 33/56] s390: fix double free of GS and RI CBs on fork() failure Date: Fri, 2 Sep 2022 14:18:53 +0200 Message-Id: <20220902121401.424236751@linuxfoundation.org> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20220902121400.219861128@linuxfoundation.org> References: <20220902121400.219861128@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Brian Foster commit 13cccafe0edcd03bf1c841de8ab8a1c8e34f77d9 upstream. The pointers for guarded storage and runtime instrumentation control blocks are stored in the thread_struct of the associated task. These pointers are initially copied on fork() via arch_dup_task_struct() and then cleared via copy_thread() before fork() returns. If fork() happens to fail after the initial task dup and before copy_thread(), the newly allocated task and associated thread_struct memory are freed via free_task() -> arch_release_task_struct(). This results in a double free of the guarded storage and runtime info structs because the fields in the failed task still refer to memory associated with the source task. This problem can manifest as a BUG_ON() in set_freepointer() (with CONFIG_SLAB_FREELIST_HARDENED enabled) or KASAN splat (if enabled) when running trinity syscall fuzz tests on s390x. To avoid this problem, clear the associated pointer fields in arch_dup_task_struct() immediately after the new task is copied. Note that the RI flag is still cleared in copy_thread() because it resides in thread stack memory and that is where stack info is copied. Signed-off-by: Brian Foster Fixes: 8d9047f8b967c ("s390/runtime instrumentation: simplify task exit han= dling") Fixes: 7b83c6297d2fc ("s390/guarded storage: simplify task exit handling") Cc: # 4.15 Reviewed-by: Gerald Schaefer Reviewed-by: Heiko Carstens Link: https://lore.kernel.org/r/20220816155407.537372-1-bfoster@redhat.com Signed-off-by: Vasily Gorbik Signed-off-by: Greg Kroah-Hartman --- arch/s390/kernel/process.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) --- a/arch/s390/kernel/process.c +++ b/arch/s390/kernel/process.c @@ -75,6 +75,18 @@ int arch_dup_task_struct(struct task_str =20 memcpy(dst, src, arch_task_struct_size); dst->thread.fpu.regs =3D dst->thread.fpu.fprs; + + /* + * Don't transfer over the runtime instrumentation or the guarded + * storage control block pointers. These fields are cleared here instead + * of in copy_thread() to avoid premature freeing of associated memory + * on fork() failure. Wait to clear the RI flag because ->stack still + * refers to the source thread. + */ + dst->thread.ri_cb =3D NULL; + dst->thread.gs_cb =3D NULL; + dst->thread.gs_bc_cb =3D NULL; + return 0; } =20 @@ -131,13 +143,11 @@ int copy_thread_tls(unsigned long clone_ frame->childregs.flags =3D 0; if (new_stackp) frame->childregs.gprs[15] =3D new_stackp; - - /* Don't copy runtime instrumentation info */ - p->thread.ri_cb =3D NULL; + /* + * Clear the runtime instrumentation flag after the above childregs + * copy. The CB pointer was already cleared in arch_dup_task_struct(). + */ frame->childregs.psw.mask &=3D ~PSW_MASK_RI; - /* Don't copy guarded storage control block */ - p->thread.gs_cb =3D NULL; - p->thread.gs_bc_cb =3D NULL; =20 /* Set a new TLS ? */ if (clone_flags & CLONE_SETTLS) {