2009-09-30 07:27:03

by Kazuya Mio

Subject: [PATCH 3/3] e4defrag: avoid unsuccessful return in non-privileged user

If non-privileged user does e4defrag, e4defrag returns 1 despite
its success. This patch fixes this problem.

Signed-off-by: Kazuya Mio <[email protected]>
---

e4defrag.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/misc/e4defrag.c b/misc/e4defrag.c
index 94f8529..98dda92 100644
--- a/misc/e4defrag.c
+++ b/misc/e4defrag.c
@@ -2025,6 +2025,7 @@ int main(int argc, char *argv[])
if (!(mode_flag & DETAIL) &&
current_uid != ROOT_UID) {
printf(" Done.\n");
+ success_flag = 1;
continue;
}

2009-09-30 18:37:20

by Greg Freemyer

Subject: Re: [PATCH 3/3] e4defrag: avoid unsuccessful return in non-privileged user

2009/9/30 Kazuya Mio <[email protected]>:
> If non-privileged user does e4defrag, e4defrag returns 1 despite
> its success. This patch fixes this problem.
>
> Signed-off-by: Kazuya Mio <[email protected]>
> ---
>
> ?e4defrag.c | ? ?1 +
> ?1 file changed, 1 insertion(+)
> diff --git a/misc/e4defrag.c b/misc/e4defrag.c
> index 94f8529..98dda92 100644
> --- a/misc/e4defrag.c
> +++ b/misc/e4defrag.c
> @@ -2025,6 +2025,7 @@ int main(int argc, char *argv[])
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?if (!(mode_flag & DETAIL) &&
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?current_uid != ROOT_UID) {
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?printf(" Done.\n");
> + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? success_flag = 1;
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?continue;
> ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?}

I should know this, but this patch made me wonder about the underlying
implementation of EXT4_IOC_MOVE_EXT.

After EXT4_IOC_MOVE_EXT is called, can userspace somehow modify the
defragged file?

ie. If I only have readonly access to a file and I call
EXT4_IOC_MOVE_EXT to replace some of the data blocks, is it possible
now for me to write data to the donor_fd and thus modify the data in
the original file?

Greg
--
Greg Freemyer
Head of EDD Tape Extraction and Processing team
Litigation Triage Solutions Specialist
http://www.linkedin.com/in/gregfreemyer
Preservation and Forensic processing of Exchange Repositories White Paper -
<http://www.norcrossgroup.com/forms/whitepapers/tng_whitepaper_fpe.html>

The Norcross Group
The Intersection of Evidence & Technology
http://www.norcrossgroup.com

2009-10-01 08:27:48

by Kazuya Mio

Subject: Re: [PATCH 3/3] e4defrag: avoid unsuccessful return in non-privileged user

2009/10/01 3:37, Greg Freemyer wrote::
> 2009/9/30 Kazuya Mio <[email protected]>:
>> If non-privileged user does e4defrag, e4defrag returns 1 despite
>> its success. This patch fixes this problem.
>>
>> Signed-off-by: Kazuya Mio <[email protected]>
>> ---
>>
>> e4defrag.c | 1 +
>> 1 file changed, 1 insertion(+)
>> diff --git a/misc/e4defrag.c b/misc/e4defrag.c
>> index 94f8529..98dda92 100644
>> --- a/misc/e4defrag.c
>> +++ b/misc/e4defrag.c
>> @@ -2025,6 +2025,7 @@ int main(int argc, char *argv[])
>> if (!(mode_flag & DETAIL) &&
>> current_uid != ROOT_UID) {
>> printf(" Done.\n");
>> + success_flag = 1;
>> continue;
>> }
>
> I should know this, but this patch made me wonder about the underlying
> implementation of EXT4_IOC_MOVE_EXT.
>
> After EXT4_IOC_MOVE_EXT is called, can userspace somehow modify the
> defragged file?
>
> ie. If I only have readonly access to a file and I call
> EXT4_IOC_MOVE_EXT to replace some of the data blocks, is it possible
> now for me to write data to the donor_fd and thus modify the data in
> the original file?
>
> Greg

Nope, EXT4_IOC_MOVE_EXT only changes original file blocks but its file
data isn't changed.

If user has readonly access to original or donor file and is both two files
owner, EXT4_IOC_MOVE_EXT succeeds. This means that the ioctl replaces
data blocks and writes original file data into replaced blocks.

Regards,

Kazuya Mio