Hi John,
Thanks for suggesting the single / few bytes encryption test. I tried doing
that, but in vain. Maybe I am going wrong somewhere else.
I will briefly tell the functions I have written and the sequence if I am doing
any mistake in the logic, please let me know.
In file.c I have added the info about the functions my_generic_file_read and
my_generic_file_write in ext2_file_operations.
For decrypting, the sequence is:
my_generic_file_read ---> my_do_generic_file_read ---> my_file_read_actor --->
my_decrypt_data
I have not made any changes in my_generic_file_read and
my_do_generic_file_read. In the function my_file_read_actor, I copy the page to
my buffer (1 page - allocated at the time of mounting) I decrypt that buffer
and pass it to the __copy_to_user() function.
for encrypting, the sequence is:
my_generic_file_write ---> my_encrypt_data
In function my_generic_file_write, between functions __copy_from_user() and
commit_write(), I am calling my_encrypt_data() by passing address of the page
that is passed to __copy_from_user()
My encrypt / decrypt routine is very basic at this time - just xoring every
byte of the page as:
*to = *to ^ 0xff; *to++;
If I change my encrypt/decrypt routines to encrypt / decrypt just first or last
byte of the page, then I get a different error saying the file is not
executable - when I try to execute it. I thought there might be a problem with
executable header, but I guess when I encrypt last byte of the page, header
should have been bypassed.
Is it something like, for executables, the data is refered in some other
functions - that is, before do_generic_file_read geting called?
Thanks and regards,
Vineet
--- On Tue 02/01, John T. Williams < [EMAIL PROTECTED] > wrote:
From: John T. Williams [mailto: [EMAIL PROTECTED]
To: [EMAIL PROTECTED], linux-kernel@vger.kernel.org
Cc: linux-c-programming@vger.kernel.org
Date: Tue, 1 Feb 2005 10:37:30 -0500
Subject: Re: Problem in accessing executable files
This is just a thought.<br><br>Text files are better able to handle small
faults. ie an extra space or<br>characters or even an unreadable piece of data
might not cause the file to<br>become unreadable by most text editors. Binary
files aren't as flexible.<br>Every bit could be an instruction to the processor
and might cause a seg<br>fault.<br><br>Just to test the theory, I would start
by making the encrypt decrypt<br>function only effect the first byte. If doing
this doesn't cause a seg<br>fault, I would recheck my decrypt encrypt algorithm
to make sure it doesn't<br>pad or expand at any point. maybe use them on a
regular file and the an<br>md5sum on the file before and after, just to make
extra sure.<br><br><br>----- Original Message ----- <br>From: "Vineet Joglekar"
<[EMAIL PROTECTED]><br>To: <linux-kernel@vger.kernel.org><br>Cc:
<linux-c-programming@vger.kernel.org><br>Sent: Tuesday, February 01, 2005 8:58
AM<br>Subject: Problem in accessing executable files<br><br><br>><br>> Hi
all,<br>><br>> I am trying to add some cryptographic functionality to ext2 file
system<br>for my masters project. I am working with kernel 2.4.21<br>><br>>
since the routines do_generic_file_read and do_generic_file_write are
used<br>in reading and writing, I am decrypting and encrypting the data in the
resp.<br>functions. This is working fine for regular data files. If I try to
copy /<br>execute executable files, I am getting segmentation fault. In
kernel<br>messages, I see same functions (read and write) getting called for
the<br>executables also. If I comment encrypt/decrypt functions, its working
fine.<br>><br>> Now since it is working for regular text files, I suppose there
is not a<br>problem in my encrypt/decrypt routines, then what might be going
wrong?<br>><br>> Thanks and regards,<br>><br>> Vineet<br>><br>>
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