From mboxrd@z Thu Jan 1 00:00:00 1970 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=-12.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 8F6FDC433DF for ; Mon, 17 Aug 2020 18:08:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 701A62072E for ; Mon, 17 Aug 2020 18:08:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597687683; bh=wp8U4N3ZbGrSZIZBQVuacLPlQFEyAk9/jAmYVSOMDrg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=KsH/vPERB2mmiSur50bGKhcpqei1PnSNh6CX65UpsZFm+QlqhO4j5ntQrzt9zB5Wc XkbULrq7rqnQ7XpFp7eoIG7jVia2+8naYtxlXAAtf2k26Vdqi1qQy5RdRx5dJ3392X 3T2sWsmtSQQ4A33Yr0QzIsi9XHw9XUObxYO3YXww= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388502AbgHQSIB (ORCPT ); Mon, 17 Aug 2020 14:08:01 -0400 Received: from mail.kernel.org ([198.145.29.99]:57900 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388458AbgHQQIb (ORCPT ); Mon, 17 Aug 2020 12:08:31 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 132E420729; Mon, 17 Aug 2020 16:08:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597680510; bh=wp8U4N3ZbGrSZIZBQVuacLPlQFEyAk9/jAmYVSOMDrg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TCqB5o4th8VUywq7bpKkQ1Q1z442OsMQvA+h2/A5aVVuVHTW72JQy4W8a+PxII/Os 5itFQmv+0fcBffgqOakMxZmPQpEoIWHm8+jpc/TiMMntgLpwlZ/L7RMqajpzVua0ri RAPiGD71yLHijEjYA1Y1vo97bAR3cYKiwSQYdGFY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Dumazet , syzbot , Andy Lutomirski , "Chang S. Bae" , Andy Lutomirski , Borislav Petkov , Brian Gerst , Dave Hansen , Denys Vlasenko , "H. Peter Anvin" , Markus T Metzger , Peter Zijlstra , Ravi Shankar , Rik van Riel , Thomas Gleixner , Ingo Molnar , Linus Torvalds , Sasha Levin , Jann Horn Subject: [PATCH 5.4 215/270] x86/fsgsbase/64: Fix NULL deref in 86_fsgsbase_read_task Date: Mon, 17 Aug 2020 17:16:56 +0200 Message-Id: <20200817143806.486151983@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200817143755.807583758@linuxfoundation.org> References: <20200817143755.807583758@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Dumazet [ Upstream commit 8ab49526b53d3172d1d8dd03a75c7d1f5bd21239 ] syzbot found its way in 86_fsgsbase_read_task() and triggered this oops: KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 0 PID: 6866 Comm: syz-executor262 Not tainted 5.8.0-syzkaller #0 RIP: 0010:x86_fsgsbase_read_task+0x16d/0x310 arch/x86/kernel/process_64.c:393 Call Trace: putreg32+0x3ab/0x530 arch/x86/kernel/ptrace.c:876 genregs32_set arch/x86/kernel/ptrace.c:1026 [inline] genregs32_set+0xa4/0x100 arch/x86/kernel/ptrace.c:1006 copy_regset_from_user include/linux/regset.h:326 [inline] ia32_arch_ptrace arch/x86/kernel/ptrace.c:1061 [inline] compat_arch_ptrace+0x36c/0xd90 arch/x86/kernel/ptrace.c:1198 __do_compat_sys_ptrace kernel/ptrace.c:1420 [inline] __se_compat_sys_ptrace kernel/ptrace.c:1389 [inline] __ia32_compat_sys_ptrace+0x220/0x2f0 kernel/ptrace.c:1389 do_syscall_32_irqs_on arch/x86/entry/common.c:84 [inline] __do_fast_syscall_32+0x57/0x80 arch/x86/entry/common.c:126 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:149 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c This can happen if ptrace() or sigreturn() pokes an LDT selector into FS or GS for a task with no LDT and something tries to read the base before a return to usermode notices the bad selector and fixes it. The fix is to make sure ldt pointer is not NULL. Fixes: 07e1d88adaae ("x86/fsgsbase/64: Fix ptrace() to read the FS/GS base accurately") Co-developed-by: Jann Horn Signed-off-by: Eric Dumazet Reported-by: syzbot Acked-by: Andy Lutomirski Cc: Chang S. Bae Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Markus T Metzger Cc: Peter Zijlstra Cc: Ravi Shankar Cc: Rik van Riel Cc: Thomas Gleixner Cc: Ingo Molnar Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- arch/x86/kernel/process_64.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index af64519b26957..da3cc3a10d63f 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -316,7 +316,7 @@ static unsigned long x86_fsgsbase_read_task(struct task_struct *task, */ mutex_lock(&task->mm->context.lock); ldt = task->mm->context.ldt; - if (unlikely(idx >= ldt->nr_entries)) + if (unlikely(!ldt || idx >= ldt->nr_entries)) base = 0; else base = get_desc_base(ldt->entries + idx); -- 2.25.1