filesystem encryption problem.

[Rohan Puri]

On 13 Jul 2015 22:08, "Amir Hezarkhani" <amir6723 at gmail.com> wrote:
>
>
> On Jul 13, 2015 1:18 AM, "Rohan Puri" <rohan.puri15 at gmail.com> wrote:
> >
> > No issues, you are welcome.
> >
> > Enjoy life,
> > Rohan
> >
> > On 13 Jul 2015 01:19, "Amir Hezarkhani" <amir6723 at gmail.com> wrote:
> >>
> >>
> >> On Jul 12, 2015 10:00 PM, "Rohan Puri" <rohan.puri15 at gmail.com> wrote:
> >> >
> >> >
> >> > On 12 Jul 2015 22:20, "Amir Hezarkhani" <amir6723 at gmail.com> wrote:
> >> > >
> >> > > Thank for replies. About copy_to_user and copy_from_user, whats
the better way?
> >> > > I dont have much experience in kernel development but I'm trying
to learn. Can you recommend me some books, documents, etc so I can learn
more about filesystems in kernel. I am also interested to learn how mmap
works because I have problems with execution of binary files in my
encrypted filesystem.
> >> > >
> >> > > On Jul 12, 2015 8:30 PM, <kernelnewbies-request at kernelnewbies.org>
wrote:
> >> > >>
> >> > >>
> >> > >>
> >> > >> On Sun, Jul 12, 2015 at 8:08 PM, Freeman Zhang <
freeman.zhang1992 at gmail.com> wrote:
> >> > >>>
> >> > >>> -------- Original Message --------
> >> > >>> > hello
> >> > >>> > I am working on adding a simple encryption to file contents in
ext4 driver
> >> > >>> > (for learning purposes) I added simple XOR encryption to
aio_read and
> >> > >>> > aio_write functions and it worked until I faced this problem:
> >> > >>> >
> >> > >>> > when I open a file in encrypted filesystem using VIM text
editor and when I
> >> > >>> > try to save it it gives me this error:
> >> > >>> >
> >> > >>> >>> pointer block id wrong
> >> > >>> >>> can not find line 1
> >> > >>> >
> >> > >>> > and it just corrupts the entire file!
> >> > >>> >
> >> > >>> > this is my aio_write function:
> >> > >>> >
> >> > >>> > aio_write_enc(struct kiocb *iocb, const struct iovec *iov,
> >> > >>> >         unsigned long nr_segs, loff_t pos)
> >> > >>> > {
> >> > >>> >     size_t i;
> >> > >>> >     ssize_t ret;
> >> > >>> >     char *data=vmalloc(sizeof(char)*iov->iov_len);
> >> > >>> >     copy_from_user(data,iov->iov_base,iov->iov_len);
> >> > >>> >
> >> > >>> >     for(i=0;i<iov->iov_len;i++)
> >> > >>> >     {
> >> > >>> >         data[i]^=5;
> >> > >>> >     }
> >> > >>> >     struct iovec iov_enc= { .iov_base = iov->iov_base,
.iov_len =
> >> > >>> > iov->iov_len };
> >> > >>> >
> >> > >>> >     copy_to_user(iov_enc.iov_base,data,iov->iov_len);
> >> > >>> >     ret=ext4_file_write(iocb,&iov_enc,nr_segs,pos);
> >> > >>> >     vfree(data);
> >> > >>> >     return ret;
> >> > >>> > }
> >> > >>> >
> >> > >>> > this just changes the data and then calls original function.
> >> > >>> >
> >> > >>> > is there anything wrong with this function? can anyone help me?
> >> > >>> >
> >> > >>> >
> >> > >>> >
> >> > >>> Hi Amir,
> >> > >>>
> >> > >>> I'm not quite sure about what's wrong with your function, but
here are
> >> > >>> two suggestions I got from the list when I did similar things:
> >> > >>>
> >> > >>> 1. wrapfs
> >> > >>> 2. ecryptfs
> >> > >>>
> >> > >>> I think you should check these two stackable filesystems if you
haven't.
> >> > >>>
> >> > >>> Hope this can help a little bit!
> >> > >>>
> >> > >>> Freeman
> >> > >>>
> >> > >>>
> >> > >>> _______________________________________________
> >> > >>> Kernelnewbies mailing list
> >> > >>> Kernelnewbies at kernelnewbies.org
> >> > >>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> >> > >>>
> >> > >>
> >> > >> Hi Amir,
> >> > >>
> >> > >> I agree with Freeman Zhang over here. The way you are doing it is
not right. There is a mechanism to create stacks of file system and you
should go down that path.
> >> > >>
> >> > >> Having said this, you should definitely debug the issue that you
are facing. Some pointers : -
> >> > >> 1. As you have already mentioned that this is happening only for
vim and not while regular read(using cat, etc), you need to check what vim
does special to read a file. I would suggest make use of strace and do
reading with and without vim, maybe you will get something of interest.
> >> > >> 2. re-read code to check, you might be messing up while write or
read.
> >> > >>
> >> > >> Apart from these some basic practices you need to follow is : -
> >> > >>
> >> > >> 1. check for error conditions, like you missed checking error
from vmalloc() and the below code will execute even if it failed, this
should be avoided.
> >> > >> 2. copy_from_user & again copying back to user is in-efficient.
>
> Yes you are right. This was the problem.
>
> >> > >>
> >> > >>
> >> > >> Enjoy life,
> >> > >> Rohan
> >> > >
> >> > >
> >> > > _______________________________________________
> >> > > Kernelnewbies mailing list
> >> > > Kernelnewbies at kernelnewbies.org
> >> > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
> >> > >
> >> >
> >> > Hi Amir,
> >> >
> >> > Please reply at the bottom. Regarding what's the better way would
depend on how you design stuff.
> >> >
> >> > Following is my recommendation :-
> >> >
> >> > For conceptual knowledge of general file systems the best would be
OS book by Prof Remzi Arpaci-Dusseau.
> >> > Excellently explained.
> >> >
> >> > For linux kernel conceptual stuff get hold of Robert love Linux
kernel development.
> >> >
> >> > Read lots of kernel generic filesystem code in FS dir. Lots of basic
functionality is implemented in helper functions present in this dir.
> >> >
> >> > Enjoy life,
> >> > Rohan
> >>
> >> Thanks a lot Rohan.  And sorry about the bad reply.
>
> Ok I solved the problem. As Rohan said, copy_from_user and then
copy_to_user was inefficient. So I removed 'copy to user' part and assigned
'data' to iov_enc.base . thanks guys and Happy codding.

Hi Amir,

Good to know.

Enjoy life,
Rohan
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