linux-kernel - Re: [Linux-NTFS-Dev] Oops with corrupted NTFS image

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Date:	Mon, 07 Jul 2008 15:26:46 +0200
From:	Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@....net>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	Eric Sesterhenn <snakebyte@....de>,
	linux-ntfs-dev@...ts.sourceforge.net,
	Anton Altaparmakov <aia21@....ac.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [Linux-NTFS-Dev] Oops with corrupted NTFS image

On 07.07.2008 15:03, Vegard Nossum wrote:
> On Mon, Jul 7, 2008 at 2:24 PM, Eric Sesterhenn <snakebyte@....de> wrote:
>   
>> (gdb) l *(ntfs_read_locked_inode+0x16c)
>> 0xc030adbc is in ntfs_read_locked_inode (fs/ntfs/time.h:90).
>> 85      static inline struct timespec ntfs2utc(const sle64 time)
>> 86      {
>> 87              struct timespec ts;
>> 88
>> 89              /* Subtract the NTFS time offset. */
>> 90              u64 t = (u64)(sle64_to_cpu(time) - NTFS_TIME_OFFSET);
>> 91              /*
>> 92               * Convert the time to 1-second intervals and the remainder to
>> 93               * 1-nano-second intervals.
>> 94               */
>> (gdb) quit
>>
>> Not sure why this happens. I checked out a fresh git tree to
>> make sure my tree isnt broken or something. Might gcc be bogus
>> or the debug information and the bug happens in reality somewhere else?
>>     

As I pointed out in my other mail, gcc compiler optimizations may have
caused a slightly off location being printed.
My suspicions about time were correct.

> Are you sure you didn't recompile/relink vmlinux after getting the
> error? If not, maybe it's gdb which gets confused (somehow) by the
> inlining.
>
> Your 'Code:' line decodes to these instructions:
>
>    0:   8b 58 08                mov    0x8(%eax),%ebx
>    3:   8b 70 0c                mov    0xc(%eax),%esi
>
> And I find this in my own compiled vmlinux at:
>
> c025bcc1:       8b 58 08                mov    0x8(%eax),%ebx
> c025bcc4:       8b 70 0c                mov    0xc(%eax),%esi
>
> which is at...
>
>     $ addr2line -e vmlinux -i c025bcc1
>     fs/ntfs/inode.c:670
>
> which is...
>
>         vi->i_mtime = ntfs2utc(si->last_data_change_time);
>
> which is probably what is causing the NULL pointer dereference.
>   

The problem of this theory is that there is no NULL pointer dereference,
unless you meant "invalid memory access".

Regards,
Carl-Daniel

-- 
http://www.hailfinger.org/

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