linux-ext4 - Re: fiemap bugs on sparse files.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 23 Feb 2011 17:34:41 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: fiemap bugs on sparse files.

On Wed, Feb 23, 2011 at 4:59 PM, Yongqiang Yang <xiaoqiangnk@...il.com> wrote:
> On Wed, Feb 23, 2011 at 5:18 AM, Chris Mason <chris.mason@...cle.com> wrote:
>> [ resend, sorry if this is a dup ]
>>
>> Hi everyone,
>>
>> We've had reports on btrfs that cp is giving us files full of zeros
>> instead of actually copying them.  It was tracked down to a bug with
>> the btrfs fiemap implementation where it was returning holes for
>> delalloc ranges.
>>
>> Newer versions of cp are trusting fiemap to tell it where the holes
>> are, which does seem like a pretty neat trick.
>>
>> I decided to give xfs and ext4 a shot with a few tests cases too, xfs
>> passed with all the ones btrfs was getting wrong, and ext4 got the basic
>> delalloc case right.
>>
>> # mkfs.ext4 /dev/xxx
>> # mount /dev/xxx /mnt
>> # dd if=/dev/zero of=/mnt/foo bs=1M count=1
>> # fiemap-test foo
>> ext:   0 logical: [       0..     255] phys:        0..     255 flags: 0x007 tot: 256
>>
>> Horray!  But once we throw a hole in, things go bad:
>>
>> # mkfs.ext4 /dev/xxx
>> # mount /dev/xxx /mnt
>> # dd if=/dev/zero of=/mnt/foo bs=1M count=1 seek=1
>> # fiemap-test foo
>> < no output >
> Actually, there is no extent in extent tree now, so
> ext4_ext_walk_space() will pass ext4_ext_fiemap_cb() a variable of
> struct ext4_ext_cache with the requested length. But in
> ext4_ext_fiemap_cb() just the paging contains start block is got
> via find_get_page(), if find_get_page() return null,
> ext4_ext_fiemap_cb()  thinks the whole request range is empty and it
> returns request range.
>
> In 1st case, find_get_page() will succeed.
>
> It seems that we should get no. of pages in page cache if
> find_get_page() fails, and correct the range to be returned.
We can call find_get_pages() with nr_pages=1 instead. And we can regulate
the range with page->index if it is not the the paging contains start block.


>
> Right?
>
> If right I will send a patch.
>
>>
>> We've got a delalloc extent after the hole and ext4 fiemap didn't find
>> it.  If I run sync to kick the delalloc out:
>>
>> # sync
>> # fiemap-test foo
>> ext:   0 logical: [     256..     511] phys:    34048..   34303 flags: 0x001 tot: 256
>
> Now, there is a extent in extent tree at least. and
> ext4_ext_walk_space() will regulate the request range to be passed to
> ext4_ext_fiemap_cb().
>>
>> fiemap-test is sitting in my /usr/local/bin, and I have no idea how it
>> got there.  It's full of pretty comments so I know it isn't mine, but
>> you can grab it here:
>>
>> http://oss.oracle.com/~mason/fiemap-test.c
>>
>> xfsqa has a fiemap program too.
>>
>> -chris
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
>> the body of a message to majordomo@...r.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
>
>
> --
> Best Wishes
> Yongqiang Yang
>



-- 
Best Wishes
Yongqiang Yang
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html