From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756894AbaH0DjE (ORCPT ); Tue, 26 Aug 2014 23:39:04 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:24258 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750834AbaH0DjC (ORCPT ); Tue, 26 Aug 2014 23:39:02 -0400 Message-ID: <53FD52C6.60603@oracle.com> Date: Tue, 26 Aug 2014 23:38:46 -0400 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 MIME-Version: 1.0 To: Oleg Nesterov , David Howells CC: Andrew Morton , richard@nod.at, Dave Jones , LKML Subject: Re: kernel: signal: NULL ptr deref when killing process References: <20140820150619.GA12706@redhat.com> <53F48402.4080302@oracle.com> <20140820141252.GA27301@redhat.com> <3200.1408638173@warthog.procyon.org.uk> <20140821171726.GB27140@redhat.com> In-Reply-To: <20140821171726.GB27140@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: acsinet21.oracle.com [141.146.126.237] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/21/2014 01:17 PM, Oleg Nesterov wrote: >> Is there a race between kill() and exit() brought on by the kill path only >> > using the RCU read lock? This doesn't prevent ->real_cred from being >> > modified, but it looks like this should, in combination with >> > delayed_put_task_struct(), prevent it from being cleared. > Yes, rcu should protect us from both delayed_put_pid() and delayed_put_task(). > Everything looks correct... And there are a lot of other similar users of > find_vpid/find_task_by_vpid/pid_task/etc under rcu, I can't recall any bug > in this area. > > I am puzzled. Note also that ->signal == NULL. Will try to think more, > but so far I have no any idea. I've hit something similar earlier today, and it might be related: [ 973.452840] BUG: unable to handle kernel NULL pointer dereference at 00000000000002b0 [ 973.455347] IP: flush_sigqueue_mask (include/linux/signal.h:118 kernel/signal.c:715) [ 973.457526] PGD 4dfdc7067 PUD 5f77d9067 PMD 0 [ 973.459216] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC [ 973.460086] Dumping ftrace buffer: [ 973.460086] (ftrace buffer empty) [ 973.460086] Modules linked in: [ 973.460086] CPU: 4 PID: 13145 Comm: trinity-c767 Not tainted 3.17.0-rc2-next-20140826-sasha-00031-gc48c9ac-dirty #1079 [ 973.460086] task: ffff880604800000 ti: ffff880586648000 task.ti: ffff880586648000 [ 973.460086] RIP: flush_sigqueue_mask (include/linux/signal.h:118 kernel/signal.c:715) [ 973.460086] RSP: 0018:ffff88058664bec8 EFLAGS: 00010046 [ 973.460086] RAX: 0000000000000000 RBX: fffffffffffff730 RCX: 0000000000010000 [ 973.460086] RDX: 0000000000000000 RSI: 00000000000002a0 RDI: ffff88058664bed8 [ 973.460086] RBP: ffff88058664bf10 R08: 0000000000000001 R09: 0000000000000001 [ 973.460086] R10: 000000000002d201 R11: 0000000000000254 R12: 0000000000000000 [ 973.460086] R13: ffff88058664bf40 R14: ffff880604800000 R15: 0000000000000010 [ 973.460086] FS: 00007fe3a3045700(0000) GS:ffff880277c00000(0000) knlGS:0000000000000000 [ 973.460086] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 973.460086] CR2: 00000000000002b0 CR3: 00000004e23d5000 CR4: 00000000000006a0 [ 973.460086] Stack: [ 973.460086] ffffffffac183690 01017fffb3247180 0000000000010000 0000000000000000 [ 973.460086] 00007fffb3247180 00007fffb3247220 0000000000000011 0000000000000000 [ 973.460086] 0000000000000000 ffff88058664bf78 ffffffffac183ef5 0000000000000000 [ 973.460086] Call Trace: [ 973.460086] ? do_sigaction (kernel/signal.c:3124 (discriminator 17)) [ 973.460086] SyS_rt_sigaction (kernel/signal.c:3360 kernel/signal.c:3341) [ 973.460086] tracesys (arch/x86/kernel/entry_64.S:542) [ 973.460086] Code: b7 49 09 d5 4d 89 6e 10 48 83 c4 08 5b 41 5c 41 5d 41 5e 41 5f 5d c3 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 48 8b 0f 31 c0 <48> 8b 56 10 48 85 ca 74 7b 55 48 f7 d1 48 89 e5 41 56 48 21 ca All code ======== 0: b7 49 mov $0x49,%bh 2: 09 d5 or %edx,%ebp 4: 4d 89 6e 10 mov %r13,0x10(%r14) 8: 48 83 c4 08 add $0x8,%rsp c: 5b pop %rbx d: 41 5c pop %r12 f: 41 5d pop %r13 11: 41 5e pop %r14 13: 41 5f pop %r15 15: 5d pop %rbp 16: c3 retq 17: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1) 1e: 00 00 00 21: 66 66 66 66 90 data32 data32 data32 xchg %ax,%ax 26: 48 8b 0f mov (%rdi),%rcx 29: 31 c0 xor %eax,%eax 2b:* 48 8b 56 10 mov 0x10(%rsi),%rdx <-- trapping instruction 2f: 48 85 ca test %rcx,%rdx 32: 74 7b je 0xaf 34: 55 push %rbp 35: 48 f7 d1 not %rcx 38: 48 89 e5 mov %rsp,%rbp 3b: 41 56 push %r14 3d: 48 21 ca and %rcx,%rdx ... Code starting with the faulting instruction =========================================== 0: 48 8b 56 10 mov 0x10(%rsi),%rdx 4: 48 85 ca test %rcx,%rdx 7: 74 7b je 0x84 9: 55 push %rbp a: 48 f7 d1 not %rcx d: 48 89 e5 mov %rsp,%rbp 10: 41 56 push %r14 12: 48 21 ca and %rcx,%rdx ... [ 973.460086] RIP flush_sigqueue_mask (include/linux/signal.h:118 kernel/signal.c:715) [ 973.460086] RSP [ 973.460086] CR2: 00000000000002b0 Thanks, Sasha