Hi all,
1 more interesting observation regarding my executable file problem.
If I copy an executable say "prac" from ext2 fs to my encrypted fs as prac1,
prac1 doesnt run on the encrypted fs. but, if I make another copy, from prac1
to normal ext2 fs, as prac2, then the prac2 executes properly on normal file
system. that means my encryption, decryption functions are getting executed
properly while using that executable as normal file to read and write, but
something else is happening when I try to execute it. I am failing to
understand what am I missing.
Vineet
--- On Sun 02/06, Vineet Joglekar < [EMAIL PROTECTED] > wrote:
From: Vineet Joglekar [mailto: [EMAIL PROTECTED]
To: [EMAIL PROTECTED], linux-kernel@vger.kernel.org
Cc: linux-c-programming@vger.kernel.org
Date: Sun, 6 Feb 2005 17:41:01 -0500 (EST)
Subject: Re: Problem in accessing executable files
<br>Hi John,<br><br>Thanks for suggesting the single / few bytes encryption
test. I tried doing that, but in vain. Maybe I am going wrong somewhere
else.<br><br>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.<br>In file.c I have
added the info about the functions my_generic_file_read and
my_generic_file_write in ext2_file_operations.<br><br>For decrypting, the
sequence is:<br>my_generic_file_read ---> my_do_generic_file_read --->
my_file_read_actor ---> my_decrypt_data<br><br>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.<br><br>for encrypting, the sequence is:<br>my_generic_file_write --->
my_encrypt_data<br><br>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()<br><br>My
encrypt / decrypt routine is very basic at this time - just xoring every byte
of the page as:<br>*to = *to ^ 0xff; *to++;<br><br>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.<br><br>Is it something like, for executables, the data is refered in
some other functions - that is, before do_generic_file_read geting
called?<br><br>Thanks and regards,<br><br>Vineet<br><br> --- On Tue 02/01, John
T. Williams < [EMAIL PROTECTED] > wrote:<br>From: John T. Williams [mailto:
[EMAIL PROTECTED]<br>To: [EMAIL PROTECTED], linux-kernel@vger.kernel.org<br>
Cc: linux-c-programming@vger.kernel.org<br>Date: Tue, 1 Feb 2005 10:37:30
-0500<br>Subject: Re: Problem in accessing executable files<br><br>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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