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,URIBL_BLOCKED, 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 2087BC433DF for ; Thu, 20 Aug 2020 11:05:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EEB842072D for ; Thu, 20 Aug 2020 11:05:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597921525; bh=0HD+PdibKx0WpBI1QWnfb7b763tjZrSmw3YiJDUjSDE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=VtN6NpKw/5BvHM/Begf6H+MWhEGHSXr/X6BnTEYmFnIcGhcZzLue6/S2aG6BOjjz4 2cW6fYD1TrGUE3Vqn0wli52Qp6cXlDs/R5lhpm+fjEfko7eFexv+r+z60E6jSIlbdW HQYYiV4+G1lB2Mz+TRzFZjx/9A8nnGayx1xpDXZ0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729392AbgHTLFO (ORCPT ); Thu, 20 Aug 2020 07:05:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:53878 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729964AbgHTKMZ (ORCPT ); Thu, 20 Aug 2020 06:12:25 -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 8A751206DA; Thu, 20 Aug 2020 10:12:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597918345; bh=0HD+PdibKx0WpBI1QWnfb7b763tjZrSmw3YiJDUjSDE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KphHcdfxT+4eYiqxXk27dw+tpnP7MP1cI3ofe5Whb4kKtTYxQdOqDE9xDRjR/o0mp HaZwpVSsMzm2gT8eO2Z0TXOmlbgWifvPvmcmyhovdH3LNwYAzh8gWaDmthfbDRSYOT v9p4eYIgRWyA3BhcJDLg+5WJm56ZTDD5jgygND9k= 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 4.14 137/228] x86/fsgsbase/64: Fix NULL deref in 86_fsgsbase_read_task Date: Thu, 20 Aug 2020 11:21:52 +0200 Message-Id: <20200820091614.435538879@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200820091607.532711107@linuxfoundation.org> References: <20200820091607.532711107@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/ptrace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 734549492a18b..dc4d27000aa35 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -374,7 +374,7 @@ static unsigned long task_seg_base(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