On Sun, Jul 12, 2015 at 8:08 PM, Freeman Zhang <freeman.zhang1992@xxxxxxxxx> wrote:
Hi Amir,-------- 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=""> > 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?
>
>
>
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
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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.
Enjoy life,
Rohan
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