2009/10/01 3:37, Greg Freemyer wrote::
> 2009/9/30 Kazuya Mio <k-mio@xxxxxxxxxxxxx>:
>> If non-privileged user does e4defrag, e4defrag returns 1 despite
>> its success. This patch fixes this problem.
>>
>> Signed-off-by: Kazuya Mio <k-mio@xxxxxxxxxxxxx>
>> ---
>>
>> 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
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