Re: [BUGFIX] NULL pointer dereference in __vm_enough_memory()

[Balbir Singh]

Andrew Morton wrote:
> On Sat, 11 Aug 2007 20:00:12 +0530 "Balbir Singh" <balbir@xxxxxxxxxxxxxxxxxx> wrote:
> 
>> On 8/11/07, Fengguang Wu <fengguang.wu@xxxxxxxxx> wrote:
> 
> hm, both people who replied to this removed Fengguang from cc.  Disagreement
> between headers and MUAs, perhaps?
> 

Oops... Not sure how that happened. I'll check my sent mail.

>>> Andrew,
>>>
>>> I'm not sure if this patch is the right fix for the bug.  But it do
>>> stops the oops message. The bug also happens in 2.6.23-rc1-mm2/2.6.23-rc2-mm2.
>>> I'm running debian/sid. The .config is attached.
>>>
>>>
>>> Unable to handle kernel NULL pointer dereference at 0000000000000138 RIP
>>>  [<ffffffff81092f66>] __vm_enough_memory+0x76/0x120
>>> PGD 7cd84067 PUD 7d9c3067 PMD 0
>>> Oops: 0000 [2] SMP
>>> CPU 1
>>> Modules linked in: eeprom lm85 hwmon_vid i2c_core tun fuse kvm snd_hda_intel snd_pcm_oss snd_mixer_oss snd_pcm snd_timer sg snd soundcore sr_mod cdrom snd_page_alloc pcspkr evdev button raid0 usbhid sd_mod uhci_hcd ehci_hcd ata_piix ahci ohci1394 ieee1394 thermal processor fan
>>> Pid: 4305, comm: khelper Tainted: G      D 2.6.23-rc2 #9
>>> RIP: 0010:[<ffffffff81092f66>]  [<ffffffff81092f66>] __vm_enough_memory+0x76/0x120
>>> RSP: 0000:ffff81007a3d1d30  EFLAGS: 00010206
>>> RAX: 0000000000000000 RBX: 0000000000000001 RCX: 000000000003e142
>>> RDX: 00000000000004f4 RSI: 0000000000000001 RDI: 0000000000000001
>>> RBP: ffff81007a3d1d40 R08: ffff81007a3d1d78 R09: 0000000000000000
>>> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
>>> R13: 0000000000000000 R14: ffff81007d0c0188 R15: ffff81007d577b18
>>> FS:  0000000000000000(0000) GS:ffff81007efa11d0(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
>>> CR2: 0000000000000138 CR3: 000000003799b000 CR4: 00000000000006e0
>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>>> Process khelper (pid: 4305, threadinfo ffff81007a3d0000, task ffff81007a30acc0)
>>> Stack:  0000000000000001 ffff81007d577b18 ffff81007a3d1d60 ffffffff811297ff
>>>  0000000000000001 ffff810037c84bb8 ffff81007a3d1da0 ffffffff81092532
>>>  ffff81007d0c0188 0000000000000000 ffff81007d577b20 0000000000000000
>>> Call Trace:
>>>  [<ffffffff811297ff>] cap_vm_enough_memory+0x2f/0x40
>>>  [<ffffffff81092532>] insert_vm_struct+0xa2/0xb0
>>>  [<ffffffff810b020e>] bprm_mm_init+0x11e/0x1b0
>>>  [<ffffffff810b1b71>] do_execve+0x81/0x220
>>>  [<ffffffff8104bf90>] __call_usermodehelper+0x0/0x90
>>>  [<ffffffff8100abc6>] sys_execve+0x46/0xb0
>>>  [<ffffffff8104bf90>] __call_usermodehelper+0x0/0x90
>>>  [<ffffffff8100cf64>] kernel_execve+0x64/0xd0
>>>  [<ffffffff8104bf90>] __call_usermodehelper+0x0/0x90
>>>  [<ffffffff8104c384>] ____call_usermodehelper+0x174/0x190
>>>  [<ffffffff8100cef8>] child_rip+0xa/0x12
>>>  [<ffffffff810356f8>] schedule_tail+0x78/0x100
>>>  [<ffffffff8100c60c>] restore_args+0x0/0x30
>>>  [<ffffffff8104c210>] ____call_usermodehelper+0x0/0x190
>>>  [<ffffffff8100ceee>] child_rip+0x0/0x12
>>>
>>>
>>> Code: 48 8b 80 38 01 00 00 48 c1 e8 05 48 29 c1 48 39 ca 0f 8c 89
>>> RIP  [<ffffffff81092f66>] __vm_enough_memory+0x76/0x120
>>>  RSP <ffff81007a3d1d30>
>>> CR2: 0000000000000138
>>>
>>> Signed-off-by: Fengguang Wu <wfg@xxxxxxxxxxxxxxxx>
>>> ---
>>>  mm/mmap.c |    3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> --- linux-2.6.23-rc2-mm2.orig/mm/mmap.c
>>> +++ linux-2.6.23-rc2-mm2/mm/mmap.c
>>> @@ -166,7 +166,8 @@ int __vm_enough_memory(long pages, int c
>>>
>>>         /* Don't let a single process grow too big:
>>>            leave 3% of the size of this process for other processes */
>>> -       allowed -= current->mm->total_vm / 32;
>>> +       if (current->mm)
>>> +               allowed -= current->mm->total_vm / 32;
>>>
>>>         /*
>>>          * cast `allowed' as a signed long because vm_committed_space
>>>
>>>
>> Shouldn't we just not stop vm accounting for kernel threads?
>>
> 
> Could be.  It'd help heaps if we knew which patch in -mm caused
> this, but from a quick peek it seems to me that mainline should be
> vulnerable as well.

Thats a valid point. It would be interesting to see what the overcommit
setting was, when the panic occurred.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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