linux-kernel - Re: general protection fault in __mem_cgroup

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Message-ID: <20180403093733.GI5501@dhcp22.suse.cz>
Date:   Tue, 3 Apr 2018 11:37:33 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     syzbot <syzbot+8a5de3cce7cdc70e9ebe@...kaller.appspotmail.com>
Cc:     cgroups@...r.kernel.org, hannes@...xchg.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com, vdavydov.dev@...il.com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: Re: general protection fault in __mem_cgroup_free

[CC Andrey]

On Sat 31-03-18 13:47:05, syzbot wrote:
> Hello,
> 
> syzbot hit the following crash on upstream commit
> 9dd2326890d89a5179967c947dab2bab34d7ddee (Fri Mar 30 17:29:47 2018 +0000)
> Merge tag 'ceph-for-4.16-rc8' of git://github.com/ceph/ceph-client
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=8a5de3cce7cdc70e9ebe
> 
> So far this crash happened 14 times on upstream.
> C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5578311367393280
> syzkaller reproducer:
> https://syzkaller.appspot.com/x/repro.syz?id=5708657048158208
> Raw console output:
> https://syzkaller.appspot.com/x/log.txt?id=6693821748346880
> Kernel config:
> https://syzkaller.appspot.com/x/.config?id=-2760467897697295172
> compiler: gcc (GCC) 7.1.1 20170620
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+8a5de3cce7cdc70e9ebe@...kaller.appspotmail.com
> It will help syzbot understand when the bug is fixed. See footer for
> details.
> If you forward the report, please keep this part and the footer.
> 
> RBP: 00000000006dcc20 R08: 0000000000000002 R09: 0000000000003335
> R10: 0000000000000000 R11: 0000000000000246 R12: 0030656c69662f2e
> R13: 00007f1747954d80 R14: ffffffffffffffff R15: 0000000000000006
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 0 PID: 4422 Comm: syzkaller101598 Not tainted 4.16.0-rc7+ #372
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:free_mem_cgroup_per_node_info mm/memcontrol.c:4111 [inline]
> RIP: 0010:__mem_cgroup_free+0x71/0x110 mm/memcontrol.c:4120

Is this a real bug or a KASAN false positive? The RIP points at
        free_percpu(pn->lruvec_stat_cpu);

Which can be NULL if we are failing to allocate per-node data in
mem_cgroup_alloc. You stack unwinder seems to point to
mem_cgroup_css_alloc->mem_cgroup_free though and that one cannot see
NULL memcg->nodeinfo[node] AFAICS.

Even if this is really mem_cgroup_alloc path then calling free_percpu
with NULL pointer should be OK. Or am I missing something?

> RSP: 0018:ffff8801accf75a8 EFLAGS: 00010206
> RAX: 0000000000000011 RBX: 0000000000000000 RCX: ffffffff8310cdfd
> RDX: 0000000000000000 RSI: 0000000000000040 RDI: 0000000000000088
> RBP: ffff8801accf75c8 R08: 0000000000000000 R09: ffff8801accf73a0
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: ffff8801ad210d40 R14: dffffc0000000000 R15: ffff8801ad210d40
> FS:  00007f1747955700(0000) GS:ffff8801db000000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000460000 CR3: 00000001cb367004 CR4: 00000000001606f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  mem_cgroup_free mm/memcontrol.c:4128 [inline]
>  mem_cgroup_css_alloc+0x403/0x19c0 mm/memcontrol.c:4239
>  css_create kernel/cgroup/cgroup.c:4729 [inline]
>  cgroup_apply_control_enable+0x44d/0xbc0 kernel/cgroup/cgroup.c:2916
>  cgroup_mkdir+0x56f/0xfc0 kernel/cgroup/cgroup.c:4938
>  kernfs_iop_mkdir+0x153/0x1e0 fs/kernfs/dir.c:1099
>  vfs_mkdir+0x390/0x600 fs/namei.c:3800
>  SYSC_mkdirat fs/namei.c:3823 [inline]
>  SyS_mkdirat+0x22b/0x2b0 fs/namei.c:3807
>  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x42/0xb7
> RIP: 0033:0x44a0c9
> RSP: 002b:00007f1747954d78 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
> RAX: ffffffffffffffda RBX: 00000000006dcc24 RCX: 000000000044a0c9
> RDX: 0000000000000020 RSI: 0000000020000280 RDI: 0000000000000005
> RBP: 00000000006dcc20 R08: 0000000000000002 R09: 0000000000003335
> R10: 0000000000000000 R11: 0000000000000246 R12: 0030656c69662f2e
> R13: 00007f1747954d80 R14: ffffffffffffffff R15: 0000000000000006
> Code: 00 00 48 89 f8 48 c1 e8 03 42 80 3c 30 00 0f 85 99 00 00 00 4f 8b a4
> e5 f0 09 00 00 49 8d bc 24 88 00 00 00 48 89 f8 48 c1 e8 03 <42> 80 3c 30 00
> 0f 85 88 00 00 00 49 8b bc 24 88 00 00 00 e8 77
> RIP: free_mem_cgroup_per_node_info mm/memcontrol.c:4111 [inline] RSP:
> ffff8801accf75a8
> RIP: __mem_cgroup_free+0x71/0x110 mm/memcontrol.c:4120 RSP: ffff8801accf75a8
> ---[ end trace 57ac07c30502ef78 ]---
> Kernel panic - not syncing: Fatal exception
-- 
Michal Hocko
SUSE Labs