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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 34016C433DB for ; Wed, 27 Jan 2021 13:35:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E90A2207B3 for ; Wed, 27 Jan 2021 13:35:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233492AbhA0NfE (ORCPT ); Wed, 27 Jan 2021 08:35:04 -0500 Received: from mail.windriver.com ([147.11.1.11]:63659 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238306AbhA0Nch (ORCPT ); Wed, 27 Jan 2021 08:32:37 -0500 Received: from pek-ygao-d1.windriver.com (pek-ygao-d1.corp.ad.wrs.com [128.224.155.99]) by mail.windriver.com (8.15.2/8.15.2) with ESMTPS id 10792Eew007852 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Thu, 7 Jan 2021 01:02:21 -0800 (PST) References: <20201209112100.47653-1-yahu.gao@windriver.com> <87zh2mprwl.fsf@x220.int.ebiederm.org> User-agent: mu4e 1.2.0; emacs 26.3 From: Gao Yahu To: "Eric W. Biederman" Cc: Yahu Gao , Alexey Dobriyan , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Al Viro Subject: Re: Review request 0/1: fs/proc: Fix NULL pointer dereference in In-reply-to: <87zh2mprwl.fsf@x220.int.ebiederm.org> Date: Thu, 07 Jan 2021 17:02:13 +0800 Message-ID: <87ft3d86i2.fsf@pek-ygao-d1> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Eric W. Biederman writes: > [Please note this e-mail is from an EXTERNAL e-mail address] > > Yahu Gao writes: > >> There is a kernel NULL pointer dereference was found in Linux system. >> The details of kernel NULL is shown at bellow. >> >> Currently, we do not have a way to provoke this fault on purpose, but >> the reproduction rate in out CI loops is high enough that we could go >> for a trace patch in black or white UP and get a reproduction in few >> weeks. >> >> Our kernel version is 4.1.21, but via analyzing the source code of the >> call trace. The upstream version should be affected. Really sorry for >> havn't reproduced this in upstream version. But it's easier to be safe >> than to prove it can't happen, right? > > Except I there are strong invariants that suggests that it takes > a memory stomp to get a NULL pointer deference here. > Sorry for late reply. I took a long time to find root cause of memory stomp, but got nothing for now:( > For the life of a proc inode PROC_I(inode)->pid should be non-NULL. > > For a non-NULL pid pointer ->tasks[PIDTYPE_PID].first simply reads > an entry out of the struct pid. Only pid needs to be non-NULL. > > So I don't see how you are getting a NULL pointer derference. > > Have you decoded the oops, looked at the assembly and seen which field > is NULL? I expec that will help you track down what is wrong. > There are two messages I had found: 1. 'Unable to handle kernel NULL pointer dereference at virtual address 00000008'. 2. In kernel 4.1.21, the members of 'struct pid' likes follow: (Apologize for missing this message at first) ... struct pid { atomic_t count; unsigned int level; /* lists of tasks that use this pid */ struct hlist_head tasks[PIDTYPE_MAX]; struct rcu_head rcu; struct upid numbers[1]; }; ... The offset of the member *tasks* from *struct pid* is 0x00000008. Based on the above message, I thought we got a NULL pointer of struct pid. Regards, Yahu > >> Details of kernel crash: >> ---------------------------------------------------------------------- >> [1446.285834] Unable to handle kernel NULL pointer dereference at >> virtual address 00000008 >> [ 1446.293943] pgd = e4af0880 >> [ 1446.296656] [00000008] *pgd=10cc3003, *pmd=04153003, *pte=00000000 >> [ 1446.302898] Internal error: Oops: 207 1 PREEMPT SMP ARM >> [ 1446.302950] Modules linked in: adkNetD ncp >> lttng_ring_buffer_client_mmap_overwrite(C) >> lttng_ring_buffer_client_mmap_discard(C) >> lttng_ring_buffer_client_discard(C) >> lttng_ring_buffer_metadata_mmap_client(C) lttng_probe_printk(C) >> lttng_probe_irq(C) lttng_ring_buffer_metadata_client(C) >> lttng_ring_buffer_client_overwrite(C) lttng_probe_signal(C) >> lttng_probe_sched(C) lttng_tracer(C) lttng_statedump(C) >> lttng_lib_ring_buffer(C) lttng_clock_plugin_arm_cntpct(C) lttng_clock(C) >> [ 1446.302963] CPU: 0 PID: 12086 Comm: netstat Tainted: G C >> 4.1.21-rt13-* #1 >> [ 1446.302967] Hardware name: Ericsson CPM1 >> [ 1446.302972] task: cbd75480 ti: c4a68000 task.ti: c4a68000 >> [ 1446.302984] PC is at pid_delete_dentry+0x8/0x18 >> [ 1446.302992] LR is at dput+0x1a8/0x2b4 >> [ 1446.303003] pc : [] lr : [] psr: 20070013 >> [ 1446.303003] sp : c4a69e88 ip : 00000000 fp : 00000000 >> [ 1446.303007] r10: 000218cc r9 : cd228000 r8 : e5f44320 >> [ 1446.303011] r7 : 00000001 r6 : 00080040 r5 : c4aa97d0 r4 : c4aa9780 >> [ 1446.303015] r3 : 00000000 r2 : cbd75480 r1 : 00000000 r0 : c4aa9780 >> [ 1446.303020] Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment >> user >> [ 1446.303026] Control: 30c5387d Table: 24af0880 DAC: 000000fd >> [ 1446.303033] Process netstat (pid: 12086, stack limit = 0xc4a68218) >> [ 1446.303039] Stack: (0xc4a69e88 to 0xc4a6a000) >> [ 1446.303052] 9e80: c4a69f70 0000a1c0 c4a69f13 00000002 e5f44320 >> cd228000 >> [ 1446.303059] 9ea0: 000218cc c0571604 c0a60bcc 00000000 00000000 >> 00000000 c4a69f20 c4a69f15 >> [ 1446.303065] 9ec0: 00003133 00000002 c4a69f13 00000000 0000001f >> c4a69f70 c35de800 0000007c >> [ 1446.303072] 9ee0: ce2b1c00 cd228000 00000001 c05747b8 c05745cc >> c35de800 0000001f 00000000 >> [ 1446.303078] 9f00: 00000004 cd228008 00020000 c05745cc 33000004 >> c0400031 c4a68000 00000400 >> [ 1446.303086] 9f20: beb78c2c cd228000 c4a69f70 00000000 cd228008 >> c0ffca90 c4a68000 00000400 >> [ 1446.303103] 9f40: beb78c2c c052cd0c bf08a774 00000400 01480080 >> 00008000 cd228000 cd228000 >> [ 1446.303114] 9f60: c040f7c8 c4a68000 00000400 c052d22c c052cd8c >> 00000000 00000021 00000000 >> [ 1446.303127] 9f80: 01480290 01480280 00007df0 ffffffea 01480060 >> 01480060 01480064 b6e424c0 >> [ 1446.303143] 9fa0: 0000008d c040f794 01480060 01480064 00000004 >> 01480080 00008000 00000000 >> [ 1446.303150] 9fc0: 01480060 01480064 b6e424c0 0000008d 01480080 >> 01480060 00035440 beb78c2c >> [ 1446.303156] 9fe0: 01480080 beb78160 b6ede59c b6edea3c 60070010 >> 00000004 00000000 00000000 >> [ 1446.303167] [] (pid_delete_dentry) from [] (dput+0x1a8/0x2b4) >> [ 1446.303176] [] (dput) from [] (proc_fill_cache+0x54/0x10c) >> [ 1446.303189] [] (proc_fill_cache) from [] >> (proc_readfd_common+0xd8/0x238) >> [ 1446.303203] [] (proc_readfd_common) from [] (iterate_dir+0x98/0x118) >> [ 1446.303217] [] (iterate_dir) from [] (SyS_getdents+0x7c/0xf0) >> [ 1446.303233] [] (SyS_getdents) from [] (__sys_trace_return+0x0/0x2c) >> [ 1446.303243] Code: e8bd0030 e12fff1e e5903028 e5133020 (e5930008) > > Eric