Intercepting system calls

Intercepting system calls

[Gaurav Saxena]

Hello all,

I am writing an application which would create a backup for the system
so that it could be restored as it is. For example I create a backup
using my application. I just do nothing at time of backup so it would
be fast. Now whenever I see any deletion I would save that file so
that I could restore it. Also I would like to see for
modification/rename. I cannot do this using inotify as I would be
notified after actual deletion/write. I don't want to use SELinux
because I want to implement this on existing installed system. I was
earlier thinking of replacing system calls for open/unlink with my
custom calls which will call my functions before actual work and then
I would decide what to do I would also want to reject unlink request
for some of the files. But as I now know that its not working in
linux>3.0 . I had also seen dazuko which is not supporting linux>3.0
yet. Also there used to be a redirfs which used to work earlier but
the latest kernel is not supported yet. I think a method could be to
replace unlink in syscall table with my unlink function but I don't
find any good method of doing that, as syscall table is no longer
exported. I would like to implement this in a kernel module instead of
modifying kernel code itself. Please suggest some method of doing
that.
Thanks to you all for your help.

--
Thanks and Regards ,
Gaurav

Re: Intercepting system calls

[Rajat Sharma]

Hi Gaurav,

I would suggest to take a wrapfs source (a null stackable file-system)
and customize it for your need. Well Erez (wrapfs author) puts his
continuous efforts in stabilizing wrapfs and porting to new kernels
and he is approachable too. In-fact he has acknowledged on of my patch
and merged it into wrapfs tree.

Agreed that you can do stuffs like patching system call table but I
(and most of us here) would categorize that as pure hack, as there
exist no framework provided by kernel to do that. Also any approach
you take to patch system call table won't be stable.

Thanks,
Rajat

On Sat, Dec 24, 2011 at 2:39 PM, Gaurav Saxena <grvsaxena419@gmail.com> wrote:
> Hello all,
>
> I am writing an application which would create a backup for the system
> so that it could be restored as it is. For example I create a backup
> using my application. I just do nothing at time of backup so it would
> be fast. Now whenever I see any deletion I would save that file so
> that I could restore it. Also I would like to see for
> modification/rename. I cannot do this using inotify as I would be
> notified after actual deletion/write. I don't want to use SELinux
> because I want to implement this on existing installed system. I was
> earlier thinking of replacing system calls for open/unlink with my
> custom calls which will call my functions before actual work and then
> I would decide what to do I would also want to reject unlink request
> for some of the files. But as I now know that its not working in
> linux>3.0 . I had also seen dazuko which is not supporting linux>3.0
> yet. Also there used to be a redirfs which used to work earlier but
> the latest kernel is not supported yet. I think a method could be to
> replace unlink in syscall table with my unlink function but I don't
> find any good method of doing that, as syscall table is no longer
> exported. I would like to implement this in a kernel module instead of
> modifying kernel code itself. Please suggest some method of doing
> that.
> Thanks to you all for your help.
>
> --
> Thanks and Regards ,
> Gaurav
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
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Re: Intercepting system calls

[Gaurav Saxena]

Hello Rajat Thanks for your reply.

On Mon, Dec 26, 2011 at 11:23 AM, Rajat Sharma <fs.rajat@gmail.com> wrote:
> Hi Gaurav,
>
> I would suggest to take a wrapfs source (a null stackable file-system)
> and customize it for your need. Well Erez (wrapfs author) puts his
> continuous efforts in stabilizing wrapfs and porting to new kernels
> and he is approachable too. In-fact he has acknowledged on of my patch
> and merged it into wrapfs tree.
Is there a way to mount "/" on such file system ? Like I want to
monitor / for changes like unlink or modified write. Would I be able
to see such changes using wrapfs. As by default on the systems "/"
would be mounted as  ext4 filesystem.
>
> Agreed that you can do stuffs like patching system call table but I
> (and most of us here) would categorize that as pure hack, as there
> exist no framework provided by kernel to do that. Also any approach
> you take to patch system call table won't be stable.
Yes I agree with you I want to do this using a method which is not a
hack, so that the support remains with all the versions of kernel
rather than a trick that works in a limited way.
>
> Thanks,
> Rajat
>
> On Sat, Dec 24, 2011 at 2:39 PM, Gaurav Saxena <grvsaxena419@gmail.com> wrote:
>> Hello all,
>>
>> I am writing an application which would create a backup for the system
>> so that it could be restored as it is. For example I create a backup
>> using my application. I just do nothing at time of backup so it would
>> be fast. Now whenever I see any deletion I would save that file so
>> that I could restore it. Also I would like to see for
>> modification/rename. I cannot do this using inotify as I would be
>> notified after actual deletion/write. I don't want to use SELinux
>> because I want to implement this on existing installed system. I was
>> earlier thinking of replacing system calls for open/unlink with my
>> custom calls which will call my functions before actual work and then
>> I would decide what to do I would also want to reject unlink request
>> for some of the files. But as I now know that its not working in
>> linux>3.0 . I had also seen dazuko which is not supporting linux>3.0
>> yet. Also there used to be a redirfs which used to work earlier but
>> the latest kernel is not supported yet. I think a method could be to
>> replace unlink in syscall table with my unlink function but I don't
>> find any good method of doing that, as syscall table is no longer
>> exported. I would like to implement this in a kernel module instead of
>> modifying kernel code itself. Please suggest some method of doing
>> that.
>> Thanks to you all for your help.
>>
>> --
>> Thanks and Regards ,
>> Gaurav
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html



-- 
Thanks and Regards ,
Gaurav
--
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the body of a message to majordomo@vger.kernel.org
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Re: Intercepting system calls

[Rajat Sharma]

wrapfs needs the underlying filesystem to be already mounted and then
it attaches itself on top of this mount point. Thats the whole idea of
stacking one to one VFS objects from wrapfs to underlying FS objects.
So it assumes that / to be already mounted. And you would want to
attach to a route volume as soon as possible, so entering wrapfs mount
entry in /etc/fstab just after / entry should be good enough.

Thanks,
Rajat

On Wed, Dec 28, 2011 at 11:29 AM, Gaurav Saxena <grvsaxena419@gmail.com> wrote:
> Hello Rajat Thanks for your reply.
>
> On Mon, Dec 26, 2011 at 11:23 AM, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> Hi Gaurav,
>>
>> I would suggest to take a wrapfs source (a null stackable file-system)
>> and customize it for your need. Well Erez (wrapfs author) puts his
>> continuous efforts in stabilizing wrapfs and porting to new kernels
>> and he is approachable too. In-fact he has acknowledged on of my patch
>> and merged it into wrapfs tree.
> Is there a way to mount "/" on such file system ? Like I want to
> monitor / for changes like unlink or modified write. Would I be able
> to see such changes using wrapfs. As by default on the systems "/"
> would be mounted as  ext4 filesystem.
>>
>> Agreed that you can do stuffs like patching system call table but I
>> (and most of us here) would categorize that as pure hack, as there
>> exist no framework provided by kernel to do that. Also any approach
>> you take to patch system call table won't be stable.
> Yes I agree with you I want to do this using a method which is not a
> hack, so that the support remains with all the versions of kernel
> rather than a trick that works in a limited way.
>>
>> Thanks,
>> Rajat
>>
>> On Sat, Dec 24, 2011 at 2:39 PM, Gaurav Saxena <grvsaxena419@gmail.com> wrote:
>>> Hello all,
>>>
>>> I am writing an application which would create a backup for the system
>>> so that it could be restored as it is. For example I create a backup
>>> using my application. I just do nothing at time of backup so it would
>>> be fast. Now whenever I see any deletion I would save that file so
>>> that I could restore it. Also I would like to see for
>>> modification/rename. I cannot do this using inotify as I would be
>>> notified after actual deletion/write. I don't want to use SELinux
>>> because I want to implement this on existing installed system. I was
>>> earlier thinking of replacing system calls for open/unlink with my
>>> custom calls which will call my functions before actual work and then
>>> I would decide what to do I would also want to reject unlink request
>>> for some of the files. But as I now know that its not working in
>>> linux>3.0 . I had also seen dazuko which is not supporting linux>3.0
>>> yet. Also there used to be a redirfs which used to work earlier but
>>> the latest kernel is not supported yet. I think a method could be to
>>> replace unlink in syscall table with my unlink function but I don't
>>> find any good method of doing that, as syscall table is no longer
>>> exported. I would like to implement this in a kernel module instead of
>>> modifying kernel code itself. Please suggest some method of doing
>>> that.
>>> Thanks to you all for your help.
>>>
>>> --
>>> Thanks and Regards ,
>>> Gaurav
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
>
> --
> Thanks and Regards ,
> Gaurav
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Intercepting system calls

[Gaurav Saxena]

Hello Rajat, Thanks for your reply.

On 12/28/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
> wrapfs needs the underlying filesystem to be already mounted and then
> it attaches itself on top of this mount point.
Ok That means it will replace the specific file system operations with
its own operations ? And then call the specific operations from
itself? Doesn't it then requires a different operation for each file
system ?
>Thats the whole idea of
> stacking one to one VFS objects from wrapfs to underlying FS objects.
> So it assumes that / to be already mounted. And you would want to
> attach to a route volume as soon as possible, so entering wrapfs mount
> entry in /etc/fstab just after / entry should be good enough.
Do I need volumes for using wrapfs ? Or simple partitioning would
suffice ? It sounds quite good I would look at this.
>
> Thanks,
> Rajat
>
> On Wed, Dec 28, 2011 at 11:29 AM, Gaurav Saxena <grvsaxena419@gmail.com>
> wrote:
>> Hello Rajat Thanks for your reply.
>>
>> On Mon, Dec 26, 2011 at 11:23 AM, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>> Hi Gaurav,
>>>
>>> I would suggest to take a wrapfs source (a null stackable file-system)
>>> and customize it for your need. Well Erez (wrapfs author) puts his
>>> continuous efforts in stabilizing wrapfs and porting to new kernels
>>> and he is approachable too. In-fact he has acknowledged on of my patch
>>> and merged it into wrapfs tree.
>> Is there a way to mount "/" on such file system ? Like I want to
>> monitor / for changes like unlink or modified write. Would I be able
>> to see such changes using wrapfs. As by default on the systems "/"
>> would be mounted as  ext4 filesystem.
>>>
>>> Agreed that you can do stuffs like patching system call table but I
>>> (and most of us here) would categorize that as pure hack, as there
>>> exist no framework provided by kernel to do that. Also any approach
>>> you take to patch system call table won't be stable.
>> Yes I agree with you I want to do this using a method which is not a
>> hack, so that the support remains with all the versions of kernel
>> rather than a trick that works in a limited way.
>>>
>>> Thanks,
>>> Rajat
>>>
>>> On Sat, Dec 24, 2011 at 2:39 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>>> wrote:
>>>> Hello all,
>>>>
>>>> I am writing an application which would create a backup for the system
>>>> so that it could be restored as it is. For example I create a backup
>>>> using my application. I just do nothing at time of backup so it would
>>>> be fast. Now whenever I see any deletion I would save that file so
>>>> that I could restore it. Also I would like to see for
>>>> modification/rename. I cannot do this using inotify as I would be
>>>> notified after actual deletion/write. I don't want to use SELinux
>>>> because I want to implement this on existing installed system. I was
>>>> earlier thinking of replacing system calls for open/unlink with my
>>>> custom calls which will call my functions before actual work and then
>>>> I would decide what to do I would also want to reject unlink request
>>>> for some of the files. But as I now know that its not working in
>>>> linux>3.0 . I had also seen dazuko which is not supporting linux>3.0
>>>> yet. Also there used to be a redirfs which used to work earlier but
>>>> the latest kernel is not supported yet. I think a method could be to
>>>> replace unlink in syscall table with my unlink function but I don't
>>>> find any good method of doing that, as syscall table is no longer
>>>> exported. I would like to implement this in a kernel module instead of
>>>> modifying kernel code itself. Please suggest some method of doing
>>>> that.
>>>> Thanks to you all for your help.
>>>>
>>>> --
>>>> Thanks and Regards ,
>>>> Gaurav
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel"
>>>> in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>>
>> --
>> Thanks and Regards ,
>> Gaurav
>


-- 
Thanks and Regards ,
Gaurav

Re: Intercepting system calls

[Rajat Sharma]

I would suggest that you go through the stackable FS documentation
maintained with wrapfs website:

http://wrapfs.filesystems.org/docs/linux-stacking/index.html

there is no replacement of fops, that again I would categorize as pure
"HACK". Here you build a stack of FS on top of existing one. so stack
fs appears as regular FS to VFS layer and as VFS to lower FS, it just
fits in between VFS and lower FS. To do it tranparent to applications
you need to mount wrapfs on the same mount point as lower fs so that
you hide direct exposure to lower FS and application can still assume
same file paths as lower FS.

Thanks,
Rajat

On Thu, Dec 29, 2011 at 12:12 PM, Gaurav Saxena <grvsaxena419@gmail.com> wrote:
> Hello Rajat, Thanks for your reply.
>
> On 12/28/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> wrapfs needs the underlying filesystem to be already mounted and then
>> it attaches itself on top of this mount point.
> Ok That means it will replace the specific file system operations with
> its own operations ? And then call the specific operations from
> itself? Doesn't it then requires a different operation for each file
> system ?
>>Thats the whole idea of
>> stacking one to one VFS objects from wrapfs to underlying FS objects.
>> So it assumes that / to be already mounted. And you would want to
>> attach to a route volume as soon as possible, so entering wrapfs mount
>> entry in /etc/fstab just after / entry should be good enough.
> Do I need volumes for using wrapfs ? Or simple partitioning would
> suffice ? It sounds quite good I would look at this.
>>
>> Thanks,
>> Rajat
>>
>> On Wed, Dec 28, 2011 at 11:29 AM, Gaurav Saxena <grvsaxena419@gmail.com>
>> wrote:
>>> Hello Rajat Thanks for your reply.
>>>
>>> On Mon, Dec 26, 2011 at 11:23 AM, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>>> Hi Gaurav,
>>>>
>>>> I would suggest to take a wrapfs source (a null stackable file-system)
>>>> and customize it for your need. Well Erez (wrapfs author) puts his
>>>> continuous efforts in stabilizing wrapfs and porting to new kernels
>>>> and he is approachable too. In-fact he has acknowledged on of my patch
>>>> and merged it into wrapfs tree.
>>> Is there a way to mount "/" on such file system ? Like I want to
>>> monitor / for changes like unlink or modified write. Would I be able
>>> to see such changes using wrapfs. As by default on the systems "/"
>>> would be mounted as  ext4 filesystem.
>>>>
>>>> Agreed that you can do stuffs like patching system call table but I
>>>> (and most of us here) would categorize that as pure hack, as there
>>>> exist no framework provided by kernel to do that. Also any approach
>>>> you take to patch system call table won't be stable.
>>> Yes I agree with you I want to do this using a method which is not a
>>> hack, so that the support remains with all the versions of kernel
>>> rather than a trick that works in a limited way.
>>>>
>>>> Thanks,
>>>> Rajat
>>>>
>>>> On Sat, Dec 24, 2011 at 2:39 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>>>> wrote:
>>>>> Hello all,
>>>>>
>>>>> I am writing an application which would create a backup for the system
>>>>> so that it could be restored as it is. For example I create a backup
>>>>> using my application. I just do nothing at time of backup so it would
>>>>> be fast. Now whenever I see any deletion I would save that file so
>>>>> that I could restore it. Also I would like to see for
>>>>> modification/rename. I cannot do this using inotify as I would be
>>>>> notified after actual deletion/write. I don't want to use SELinux
>>>>> because I want to implement this on existing installed system. I was
>>>>> earlier thinking of replacing system calls for open/unlink with my
>>>>> custom calls which will call my functions before actual work and then
>>>>> I would decide what to do I would also want to reject unlink request
>>>>> for some of the files. But as I now know that its not working in
>>>>> linux>3.0 . I had also seen dazuko which is not supporting linux>3.0
>>>>> yet. Also there used to be a redirfs which used to work earlier but
>>>>> the latest kernel is not supported yet. I think a method could be to
>>>>> replace unlink in syscall table with my unlink function but I don't
>>>>> find any good method of doing that, as syscall table is no longer
>>>>> exported. I would like to implement this in a kernel module instead of
>>>>> modifying kernel code itself. Please suggest some method of doing
>>>>> that.
>>>>> Thanks to you all for your help.
>>>>>
>>>>> --
>>>>> Thanks and Regards ,
>>>>> Gaurav
>>>>> --
>>>>> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel"
>>>>> in
>>>>> the body of a message to majordomo@vger.kernel.org
>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>>
>>>
>>> --
>>> Thanks and Regards ,
>>> Gaurav
>>
>
>
> --
> Thanks and Regards ,
> Gaurav
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Intercepting system calls

[Gaurav Saxena]

On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
> I would suggest that you go through the stackable FS documentation
> maintained with wrapfs website:
>
> http://wrapfs.filesystems.org/docs/linux-stacking/index.html
>
> there is no replacement of fops, that again I would categorize as pure
> "HACK". Here you build a stack of FS on top of existing one. so stack
> fs appears as regular FS to VFS layer and as VFS to lower FS, it just
> fits in between VFS and lower FS. To do it tranparent to applications
> you need to mount wrapfs on the same mount point as lower fs so that
> you hide direct exposure to lower FS and application can still assume
> same file paths as lower FS.
I am going through their documentation. I see this means I could
intercept in between for filesystems on which I mount this file system
and thus could do what I want to do. I can skip entire system calls I
suppose. Also I am thinking of KProbes is it possible to skip system
call using kprobes ?
Thanks a lot for your help.
>
> Thanks,
> Rajat
>
> On Thu, Dec 29, 2011 at 12:12 PM, Gaurav Saxena <grvsaxena419@gmail.com>
> wrote:
>> Hello Rajat, Thanks for your reply.
>>
>> On 12/28/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>> wrapfs needs the underlying filesystem to be already mounted and then
>>> it attaches itself on top of this mount point.
>> Ok That means it will replace the specific file system operations with
>> its own operations ? And then call the specific operations from
>> itself? Doesn't it then requires a different operation for each file
>> system ?
>>>Thats the whole idea of
>>> stacking one to one VFS objects from wrapfs to underlying FS objects.
>>> So it assumes that / to be already mounted. And you would want to
>>> attach to a route volume as soon as possible, so entering wrapfs mount
>>> entry in /etc/fstab just after / entry should be good enough.
>> Do I need volumes for using wrapfs ? Or simple partitioning would
>> suffice ? It sounds quite good I would look at this.
>>>
>>> Thanks,
>>> Rajat
>>>
>>> On Wed, Dec 28, 2011 at 11:29 AM, Gaurav Saxena <grvsaxena419@gmail.com>
>>> wrote:
>>>> Hello Rajat Thanks for your reply.
>>>>
>>>> On Mon, Dec 26, 2011 at 11:23 AM, Rajat Sharma <fs.rajat@gmail.com>
>>>> wrote:
>>>>> Hi Gaurav,
>>>>>
>>>>> I would suggest to take a wrapfs source (a null stackable file-system)
>>>>> and customize it for your need. Well Erez (wrapfs author) puts his
>>>>> continuous efforts in stabilizing wrapfs and porting to new kernels
>>>>> and he is approachable too. In-fact he has acknowledged on of my patch
>>>>> and merged it into wrapfs tree.
>>>> Is there a way to mount "/" on such file system ? Like I want to
>>>> monitor / for changes like unlink or modified write. Would I be able
>>>> to see such changes using wrapfs. As by default on the systems "/"
>>>> would be mounted as  ext4 filesystem.
>>>>>
>>>>> Agreed that you can do stuffs like patching system call table but I
>>>>> (and most of us here) would categorize that as pure hack, as there
>>>>> exist no framework provided by kernel to do that. Also any approach
>>>>> you take to patch system call table won't be stable.
>>>> Yes I agree with you I want to do this using a method which is not a
>>>> hack, so that the support remains with all the versions of kernel
>>>> rather than a trick that works in a limited way.
>>>>>
>>>>> Thanks,
>>>>> Rajat
>>>>>
>>>>> On Sat, Dec 24, 2011 at 2:39 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>>>>> wrote:
>>>>>> Hello all,
>>>>>>
>>>>>> I am writing an application which would create a backup for the system
>>>>>> so that it could be restored as it is. For example I create a backup
>>>>>> using my application. I just do nothing at time of backup so it would
>>>>>> be fast. Now whenever I see any deletion I would save that file so
>>>>>> that I could restore it. Also I would like to see for
>>>>>> modification/rename. I cannot do this using inotify as I would be
>>>>>> notified after actual deletion/write. I don't want to use SELinux
>>>>>> because I want to implement this on existing installed system. I was
>>>>>> earlier thinking of replacing system calls for open/unlink with my
>>>>>> custom calls which will call my functions before actual work and then
>>>>>> I would decide what to do I would also want to reject unlink request
>>>>>> for some of the files. But as I now know that its not working in
>>>>>> linux>3.0 . I had also seen dazuko which is not supporting linux>3.0
>>>>>> yet. Also there used to be a redirfs which used to work earlier but
>>>>>> the latest kernel is not supported yet. I think a method could be to
>>>>>> replace unlink in syscall table with my unlink function but I don't
>>>>>> find any good method of doing that, as syscall table is no longer
>>>>>> exported. I would like to implement this in a kernel module instead of
>>>>>> modifying kernel code itself. Please suggest some method of doing
>>>>>> that.
>>>>>> Thanks to you all for your help.
>>>>>>
>>>>>> --
>>>>>> Thanks and Regards ,
>>>>>> Gaurav
>>>>>> --
>>>>>> To unsubscribe from this list: send the line "unsubscribe
>>>>>> linux-fsdevel"
>>>>>> in
>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>
>>>>
>>>>
>>>> --
>>>> Thanks and Regards ,
>>>> Gaurav
>>>
>>
>>
>> --
>> Thanks and Regards ,
>> Gaurav
>


-- 
Thanks and Regards ,
Gaurav

Re: Intercepting system calls

[Rajat Sharma]

Well kprobe is:

1. meant to instrument debugging while developing
2. Is configured with kernel configuration parameters which you can
not guarantee to be configured on deployment site.
3. slower as it works with debugger break point instruction and single
stepping mode.
4. probing into an instruction and altering behavior might not scale
across kernel version and interface changes.

But yes, you can technically capture any kernel instruction's virtual
address and probe into it. Building solution on top of such
instrumentation -- HACK!! :)

Did you try looking for LSM as well?

-Rajat

On Thu, Dec 29, 2011 at 3:53 PM, Gaurav Saxena <grvsaxena419@gmail.com> wrote:
> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> I would suggest that you go through the stackable FS documentation
>> maintained with wrapfs website:
>>
>> http://wrapfs.filesystems.org/docs/linux-stacking/index.html
>>
>> there is no replacement of fops, that again I would categorize as pure
>> "HACK". Here you build a stack of FS on top of existing one. so stack
>> fs appears as regular FS to VFS layer and as VFS to lower FS, it just
>> fits in between VFS and lower FS. To do it tranparent to applications
>> you need to mount wrapfs on the same mount point as lower fs so that
>> you hide direct exposure to lower FS and application can still assume
>> same file paths as lower FS.
> I am going through their documentation. I see this means I could
> intercept in between for filesystems on which I mount this file system
> and thus could do what I want to do. I can skip entire system calls I
> suppose. Also I am thinking of KProbes is it possible to skip system
> call using kprobes ?
> Thanks a lot for your help.
>>
>> Thanks,
>> Rajat
>>
>> On Thu, Dec 29, 2011 at 12:12 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>> wrote:
>>> Hello Rajat, Thanks for your reply.
>>>
>>> On 12/28/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>>> wrapfs needs the underlying filesystem to be already mounted and then
>>>> it attaches itself on top of this mount point.
>>> Ok That means it will replace the specific file system operations with
>>> its own operations ? And then call the specific operations from
>>> itself? Doesn't it then requires a different operation for each file
>>> system ?
>>>>Thats the whole idea of
>>>> stacking one to one VFS objects from wrapfs to underlying FS objects.
>>>> So it assumes that / to be already mounted. And you would want to
>>>> attach to a route volume as soon as possible, so entering wrapfs mount
>>>> entry in /etc/fstab just after / entry should be good enough.
>>> Do I need volumes for using wrapfs ? Or simple partitioning would
>>> suffice ? It sounds quite good I would look at this.
>>>>
>>>> Thanks,
>>>> Rajat
>>>>
>>>> On Wed, Dec 28, 2011 at 11:29 AM, Gaurav Saxena <grvsaxena419@gmail.com>
>>>> wrote:
>>>>> Hello Rajat Thanks for your reply.
>>>>>
>>>>> On Mon, Dec 26, 2011 at 11:23 AM, Rajat Sharma <fs.rajat@gmail.com>
>>>>> wrote:
>>>>>> Hi Gaurav,
>>>>>>
>>>>>> I would suggest to take a wrapfs source (a null stackable file-system)
>>>>>> and customize it for your need. Well Erez (wrapfs author) puts his
>>>>>> continuous efforts in stabilizing wrapfs and porting to new kernels
>>>>>> and he is approachable too. In-fact he has acknowledged on of my patch
>>>>>> and merged it into wrapfs tree.
>>>>> Is there a way to mount "/" on such file system ? Like I want to
>>>>> monitor / for changes like unlink or modified write. Would I be able
>>>>> to see such changes using wrapfs. As by default on the systems "/"
>>>>> would be mounted as  ext4 filesystem.
>>>>>>
>>>>>> Agreed that you can do stuffs like patching system call table but I
>>>>>> (and most of us here) would categorize that as pure hack, as there
>>>>>> exist no framework provided by kernel to do that. Also any approach
>>>>>> you take to patch system call table won't be stable.
>>>>> Yes I agree with you I want to do this using a method which is not a
>>>>> hack, so that the support remains with all the versions of kernel
>>>>> rather than a trick that works in a limited way.
>>>>>>
>>>>>> Thanks,
>>>>>> Rajat
>>>>>>
>>>>>> On Sat, Dec 24, 2011 at 2:39 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>>>>>> wrote:
>>>>>>> Hello all,
>>>>>>>
>>>>>>> I am writing an application which would create a backup for the system
>>>>>>> so that it could be restored as it is. For example I create a backup
>>>>>>> using my application. I just do nothing at time of backup so it would
>>>>>>> be fast. Now whenever I see any deletion I would save that file so
>>>>>>> that I could restore it. Also I would like to see for
>>>>>>> modification/rename. I cannot do this using inotify as I would be
>>>>>>> notified after actual deletion/write. I don't want to use SELinux
>>>>>>> because I want to implement this on existing installed system. I was
>>>>>>> earlier thinking of replacing system calls for open/unlink with my
>>>>>>> custom calls which will call my functions before actual work and then
>>>>>>> I would decide what to do I would also want to reject unlink request
>>>>>>> for some of the files. But as I now know that its not working in
>>>>>>> linux>3.0 . I had also seen dazuko which is not supporting linux>3.0
>>>>>>> yet. Also there used to be a redirfs which used to work earlier but
>>>>>>> the latest kernel is not supported yet. I think a method could be to
>>>>>>> replace unlink in syscall table with my unlink function but I don't
>>>>>>> find any good method of doing that, as syscall table is no longer
>>>>>>> exported. I would like to implement this in a kernel module instead of
>>>>>>> modifying kernel code itself. Please suggest some method of doing
>>>>>>> that.
>>>>>>> Thanks to you all for your help.
>>>>>>>
>>>>>>> --
>>>>>>> Thanks and Regards ,
>>>>>>> Gaurav
>>>>>>> --
>>>>>>> To unsubscribe from this list: send the line "unsubscribe
>>>>>>> linux-fsdevel"
>>>>>>> in
>>>>>>> the body of a message to majordomo@vger.kernel.org
>>>>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Thanks and Regards ,
>>>>> Gaurav
>>>>
>>>
>>>
>>> --
>>> Thanks and Regards ,
>>> Gaurav
>>
>
>
> --
> Thanks and Regards ,
> Gaurav
--
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Re: Intercepting system calls

[Gaurav Saxena]

On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
> Well kprobe is:
>
> 1. meant to instrument debugging while developing
> 2. Is configured with kernel configuration parameters which you can
> not guarantee to be configured on deployment site.
> 3. slower as it works with debugger break point instruction and single
> stepping mode.
> 4. probing into an instruction and altering behavior might not scale
> across kernel version and interface changes.
>
> But yes, you can technically capture any kernel instruction's virtual
> address and probe into it. Building solution on top of such
> instrumentation -- HACK!! :)
Ok Thanks. I see it will be real slow then as its only a debugging
mechanism, I also found a hack which uses a kprobe based approach and
adds a jump code to beginning of system calls. Yes I agree with you ,
I don't want hack which needs to be changed with kernel versions or
depends on configuration of kernel.
I will give a try to wrapfs today. :) Is it too a hack ?
>
> Did you try looking for LSM as well?
LSM projects like SELinux ? Actually they need kernel rebuild/
reinstall thus I would try not to go for such options.
>
> -Rajat
>

-- 
Thanks and Regards ,
Gaurav

Re: Intercepting system calls

[Rajat Sharma]

well ecryptfs which ships with mainline linux kernel is based upon
stackable approach (wrapfs), do you call it hack? :)

On Thu, Dec 29, 2011 at 5:36 PM, Gaurav Saxena <grvsaxena419@gmail.com> wrote:
> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> Well kprobe is:
>>
>> 1. meant to instrument debugging while developing
>> 2. Is configured with kernel configuration parameters which you can
>> not guarantee to be configured on deployment site.
>> 3. slower as it works with debugger break point instruction and single
>> stepping mode.
>> 4. probing into an instruction and altering behavior might not scale
>> across kernel version and interface changes.
>>
>> But yes, you can technically capture any kernel instruction's virtual
>> address and probe into it. Building solution on top of such
>> instrumentation -- HACK!! :)
> Ok Thanks. I see it will be real slow then as its only a debugging
> mechanism, I also found a hack which uses a kprobe based approach and
> adds a jump code to beginning of system calls. Yes I agree with you ,
> I don't want hack which needs to be changed with kernel versions or
> depends on configuration of kernel.
> I will give a try to wrapfs today. :) Is it too a hack ?
>>
>> Did you try looking for LSM as well?
> LSM projects like SELinux ? Actually they need kernel rebuild/
> reinstall thus I would try not to go for such options.
>>
>> -Rajat
>>
>
> --
> Thanks and Regards ,
> Gaurav

Re: Intercepting system calls

[Gaurav Saxena]

On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
> well ecryptfs which ships with mainline linux kernel is based upon
> stackable approach (wrapfs), do you call it hack? :)
Ok. I will try to use wrapfs but it seems its quite old and inactive
too. I would have to write a new filesystem extending wrapfs it seems.
I would work upon it and ask for help when I get problems. :)
Thanks a lot for helping me.
>
> On Thu, Dec 29, 2011 at 5:36 PM, Gaurav Saxena <grvsaxena419@gmail.com>
> wrote:
>> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>> Well kprobe is:
>>>
>>> 1. meant to instrument debugging while developing
>>> 2. Is configured with kernel configuration parameters which you can
>>> not guarantee to be configured on deployment site.
>>> 3. slower as it works with debugger break point instruction and single
>>> stepping mode.
>>> 4. probing into an instruction and altering behavior might not scale
>>> across kernel version and interface changes.
>>>
>>> But yes, you can technically capture any kernel instruction's virtual
>>> address and probe into it. Building solution on top of such
>>> instrumentation -- HACK!! :)
>> Ok Thanks. I see it will be real slow then as its only a debugging
>> mechanism, I also found a hack which uses a kprobe based approach and
>> adds a jump code to beginning of system calls. Yes I agree with you ,
>> I don't want hack which needs to be changed with kernel versions or
>> depends on configuration of kernel.
>> I will give a try to wrapfs today. :) Is it too a hack ?
>>>
>>> Did you try looking for LSM as well?
>> LSM projects like SELinux ? Actually they need kernel rebuild/
>> reinstall thus I would try not to go for such options.
>>>
>>> -Rajat
>>>
>>
>> --
>> Thanks and Regards ,
>> Gaurav
>


-- 
Thanks and Regards ,
Gaurav

Re: Intercepting system calls

[Rajat Sharma]

You could probably trim down ecryptfs and customize it as per your
need. It has advantage of being in mainline. Just remove encryption
part of it. I wish if Linux provided a framework to do the same.

-Rajat

On Thu, Dec 29, 2011 at 6:37 PM, rohan puri <rohan.puri15@gmail.com> wrote:
>
>
> On Thu, Dec 29, 2011 at 6:02 PM, Gaurav Saxena <grvsaxena419@gmail.com>
> wrote:
>>
>> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> > well ecryptfs which ships with mainline linux kernel is based upon
>> > stackable approach (wrapfs), do you call it hack? :)
>> Ok. I will try to use wrapfs but it seems its quite old and inactive
>> too. I would have to write a new filesystem extending wrapfs it seems.
>> I would work upon it and ask for help when I get problems. :)
>> Thanks a lot for helping me.
>> >
>> > On Thu, Dec 29, 2011 at 5:36 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>> > wrote:
>> >> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> >>> Well kprobe is:
>> >>>
>> >>> 1. meant to instrument debugging while developing
>> >>> 2. Is configured with kernel configuration parameters which you can
>> >>> not guarantee to be configured on deployment site.
>> >>> 3. slower as it works with debugger break point instruction and single
>> >>> stepping mode.
>> >>> 4. probing into an instruction and altering behavior might not scale
>> >>> across kernel version and interface changes.
>> >>>
>> >>> But yes, you can technically capture any kernel instruction's virtual
>> >>> address and probe into it. Building solution on top of such
>> >>> instrumentation -- HACK!! :)
>> >> Ok Thanks. I see it will be real slow then as its only a debugging
>> >> mechanism, I also found a hack which uses a kprobe based approach and
>> >> adds a jump code to beginning of system calls. Yes I agree with you ,
>> >> I don't want hack which needs to be changed with kernel versions or
>> >> depends on configuration of kernel.
>> >> I will give a try to wrapfs today. :) Is it too a hack ?
>> >>>
>> >>> Did you try looking for LSM as well?
>> >> LSM projects like SELinux ? Actually they need kernel rebuild/
>> >> reinstall thus I would try not to go for such options.
>> >>>
>> >>> -Rajat
>> >>>
>> >>
>> >> --
>> >> Thanks and Regards ,
>> >> Gaurav
>> >
>>
>>
>> --
>> Thanks and Regards ,
>> Gaurav
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel"
>> in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
> Just to let you know, you can make use of
> http://gauravnaigaonkar.web.officelive.com/Documents/hw2.txt as a reference
> on how to write a stackable file system. This is for linux kernel version
> 2.6.26
>
> Regards,
> Rohan Puri
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Intercepting system calls

[Gaurav Saxena]

On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
> You could probably trim down ecryptfs and customize it as per your
> need. It has advantage of being in mainline. Just remove encryption
> part of it. I wish if Linux provided a framework to do the same.
Ok, I will do that ecryptfs is part of kernel source I see. I would
try doing the same. Yes ofcourse that would have been really great.
Thanks for your help :).
>
> -Rajat
>
> On Thu, Dec 29, 2011 at 6:37 PM, rohan puri <rohan.puri15@gmail.com> wrote:
>>
>>
>> On Thu, Dec 29, 2011 at 6:02 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>> wrote:
>>>
>>> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>> > well ecryptfs which ships with mainline linux kernel is based upon
>>> > stackable approach (wrapfs), do you call it hack? :)
>>> Ok. I will try to use wrapfs but it seems its quite old and inactive
>>> too. I would have to write a new filesystem extending wrapfs it seems.
>>> I would work upon it and ask for help when I get problems. :)
>>> Thanks a lot for helping me.
>>> >
>>> > On Thu, Dec 29, 2011 at 5:36 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>>> > wrote:
>>> >> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>> >>> Well kprobe is:
>>> >>>
>>> >>> 1. meant to instrument debugging while developing
>>> >>> 2. Is configured with kernel configuration parameters which you can
>>> >>> not guarantee to be configured on deployment site.
>>> >>> 3. slower as it works with debugger break point instruction and
>>> >>> single
>>> >>> stepping mode.
>>> >>> 4. probing into an instruction and altering behavior might not scale
>>> >>> across kernel version and interface changes.
>>> >>>
>>> >>> But yes, you can technically capture any kernel instruction's virtual
>>> >>> address and probe into it. Building solution on top of such
>>> >>> instrumentation -- HACK!! :)
>>> >> Ok Thanks. I see it will be real slow then as its only a debugging
>>> >> mechanism, I also found a hack which uses a kprobe based approach and
>>> >> adds a jump code to beginning of system calls. Yes I agree with you ,
>>> >> I don't want hack which needs to be changed with kernel versions or
>>> >> depends on configuration of kernel.
>>> >> I will give a try to wrapfs today. :) Is it too a hack ?
>>> >>>
>>> >>> Did you try looking for LSM as well?
>>> >> LSM projects like SELinux ? Actually they need kernel rebuild/
>>> >> reinstall thus I would try not to go for such options.
>>> >>>
>>> >>> -Rajat
>>> >>>
>>> >>
>>> >> --
>>> >> Thanks and Regards ,
>>> >> Gaurav
>>> >
>>>
>>>
>>> --
>>> Thanks and Regards ,
>>> Gaurav
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel"
>>> in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>> Just to let you know, you can make use of
>> http://gauravnaigaonkar.web.officelive.com/Documents/hw2.txt as a
>> reference
>> on how to write a stackable file system. This is for linux kernel version
>> 2.6.26
>>
>> Regards,
>> Rohan Puri
>


-- 
Thanks and Regards ,
Gaurav

Re: Intercepting system calls

[Gaurav Saxena]

Do I need to change kernel code in order to get stackable fs working ?
Also I tried to change ecryptfs but it doesn't compile outside the
kernel directory. Could a stackable fs be loaded as a kernel module ?

On 12/29/11, Gaurav Saxena <grvsaxena419@gmail.com> wrote:
> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> You could probably trim down ecryptfs and customize it as per your
>> need. It has advantage of being in mainline. Just remove encryption
>> part of it. I wish if Linux provided a framework to do the same.
> Ok, I will do that ecryptfs is part of kernel source I see. I would
> try doing the same. Yes ofcourse that would have been really great.
> Thanks for your help :).
>>
>> -Rajat
>>
>> On Thu, Dec 29, 2011 at 6:37 PM, rohan puri <rohan.puri15@gmail.com>
>> wrote:
>>>
>>>
>>> On Thu, Dec 29, 2011 at 6:02 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>>> wrote:
>>>>
>>>> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>>> > well ecryptfs which ships with mainline linux kernel is based upon
>>>> > stackable approach (wrapfs), do you call it hack? :)
>>>> Ok. I will try to use wrapfs but it seems its quite old and inactive
>>>> too. I would have to write a new filesystem extending wrapfs it seems.
>>>> I would work upon it and ask for help when I get problems. :)
>>>> Thanks a lot for helping me.
>>>> >
>>>> > On Thu, Dec 29, 2011 at 5:36 PM, Gaurav Saxena
>>>> > <grvsaxena419@gmail.com>
>>>> > wrote:
>>>> >> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>>> >>> Well kprobe is:
>>>> >>>
>>>> >>> 1. meant to instrument debugging while developing
>>>> >>> 2. Is configured with kernel configuration parameters which you can
>>>> >>> not guarantee to be configured on deployment site.
>>>> >>> 3. slower as it works with debugger break point instruction and
>>>> >>> single
>>>> >>> stepping mode.
>>>> >>> 4. probing into an instruction and altering behavior might not
>>>> >>> scale
>>>> >>> across kernel version and interface changes.
>>>> >>>
>>>> >>> But yes, you can technically capture any kernel instruction's
>>>> >>> virtual
>>>> >>> address and probe into it. Building solution on top of such
>>>> >>> instrumentation -- HACK!! :)
>>>> >> Ok Thanks. I see it will be real slow then as its only a debugging
>>>> >> mechanism, I also found a hack which uses a kprobe based approach
>>>> >> and
>>>> >> adds a jump code to beginning of system calls. Yes I agree with you
>>>> >> ,
>>>> >> I don't want hack which needs to be changed with kernel versions or
>>>> >> depends on configuration of kernel.
>>>> >> I will give a try to wrapfs today. :) Is it too a hack ?
>>>> >>>
>>>> >>> Did you try looking for LSM as well?
>>>> >> LSM projects like SELinux ? Actually they need kernel rebuild/
>>>> >> reinstall thus I would try not to go for such options.
>>>> >>>
>>>> >>> -Rajat
>>>> >>>
>>>> >>
>>>> >> --
>>>> >> Thanks and Regards ,
>>>> >> Gaurav
>>>> >
>>>>
>>>>
>>>> --
>>>> Thanks and Regards ,
>>>> Gaurav
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe
>>>> linux-fsdevel"
>>>> in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>
>>>
>>> Just to let you know, you can make use of
>>> http://gauravnaigaonkar.web.officelive.com/Documents/hw2.txt as a
>>> reference
>>> on how to write a stackable file system. This is for linux kernel
>>> version
>>> 2.6.26
>>>
>>> Regards,
>>> Rohan Puri
>>
>
>
> --
> Thanks and Regards ,
> Gaurav
>


-- 
Thanks and Regards ,
Gaurav

Re: Intercepting system calls

[Gaurav Saxena]

Hello again.
I started on wrapfs, its nice and I can use it for my purpose but I
need help on using it transparently. I modified unlink call a bit and
so I now want to test wrapfs on my system. I could use it using
> mount -t wrapfs /root /mnt/tmp
Now if I unlink files from /mnt/tmp wrapfa unlink is called but I want
to do this transparently ie. I want to mount /root on itself so that
requests to delete files in /root goes through wrapfs. But I am unable
to do this I tried
> mount -t wrapfs -O /root
As described for overlay mounts but this is not working as this does
not result in mount call. How can I use wrapfs for overlay mounts ? Or
this is not possible ?

On Thu, Dec 29, 2011 at 6:42 PM, Rajat Sharma <fs.rajat@gmail.com> wrote:
> You could probably trim down ecryptfs and customize it as per your
> need. It has advantage of being in mainline. Just remove encryption
> part of it. I wish if Linux provided a framework to do the same.
>
> -Rajat
>
> On Thu, Dec 29, 2011 at 6:37 PM, rohan puri <rohan.puri15@gmail.com> wrote:
>>
>>
>> On Thu, Dec 29, 2011 at 6:02 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>> wrote:
>>>
>>> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>> > well ecryptfs which ships with mainline linux kernel is based upon
>>> > stackable approach (wrapfs), do you call it hack? :)
>>> Ok. I will try to use wrapfs but it seems its quite old and inactive
>>> too. I would have to write a new filesystem extending wrapfs it seems.
>>> I would work upon it and ask for help when I get problems. :)
>>> Thanks a lot for helping me.
>>> >
>>> > On Thu, Dec 29, 2011 at 5:36 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>>> > wrote:
>>> >> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>>> >>> Well kprobe is:
>>> >>>
>>> >>> 1. meant to instrument debugging while developing
>>> >>> 2. Is configured with kernel configuration parameters which you can
>>> >>> not guarantee to be configured on deployment site.
>>> >>> 3. slower as it works with debugger break point instruction and single
>>> >>> stepping mode.
>>> >>> 4. probing into an instruction and altering behavior might not scale
>>> >>> across kernel version and interface changes.
>>> >>>
>>> >>> But yes, you can technically capture any kernel instruction's virtual
>>> >>> address and probe into it. Building solution on top of such
>>> >>> instrumentation -- HACK!! :)
>>> >> Ok Thanks. I see it will be real slow then as its only a debugging
>>> >> mechanism, I also found a hack which uses a kprobe based approach and
>>> >> adds a jump code to beginning of system calls. Yes I agree with you ,
>>> >> I don't want hack which needs to be changed with kernel versions or
>>> >> depends on configuration of kernel.
>>> >> I will give a try to wrapfs today. :) Is it too a hack ?
>>> >>>
>>> >>> Did you try looking for LSM as well?
>>> >> LSM projects like SELinux ? Actually they need kernel rebuild/
>>> >> reinstall thus I would try not to go for such options.
>>> >>>
>>> >>> -Rajat
>>> >>>
>>> >>
>>> >> --
>>> >> Thanks and Regards ,
>>> >> Gaurav
>>> >
>>>
>>>
>>> --
>>> Thanks and Regards ,
>>> Gaurav
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel"
>>> in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>> Just to let you know, you can make use of
>> http://gauravnaigaonkar.web.officelive.com/Documents/hw2.txt as a reference
>> on how to write a stackable file system. This is for linux kernel version
>> 2.6.26
>>
>> Regards,
>> Rohan Puri



-- 
Thanks and Regards ,
Gaurav
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: Intercepting system calls

[Gaurav Saxena]

Hello Rohan , Thanks a lot for help. :)

On 12/29/11, rohan puri <rohan.puri15@gmail.com> wrote:
> On Thu, Dec 29, 2011 at 6:02 PM, Gaurav Saxena
> <grvsaxena419@gmail.com>wrote:
>
>> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> > well ecryptfs which ships with mainline linux kernel is based upon
>> > stackable approach (wrapfs), do you call it hack? :)
>> Ok. I will try to use wrapfs but it seems its quite old and inactive
>> too. I would have to write a new filesystem extending wrapfs it seems.
>> I would work upon it and ask for help when I get problems. :)
>> Thanks a lot for helping me.
>> >
>> > On Thu, Dec 29, 2011 at 5:36 PM, Gaurav Saxena <grvsaxena419@gmail.com>
>> > wrote:
>> >> On 12/29/11, Rajat Sharma <fs.rajat@gmail.com> wrote:
>> >>> Well kprobe is:
>> >>>
>> >>> 1. meant to instrument debugging while developing
>> >>> 2. Is configured with kernel configuration parameters which you can
>> >>> not guarantee to be configured on deployment site.
>> >>> 3. slower as it works with debugger break point instruction and single
>> >>> stepping mode.
>> >>> 4. probing into an instruction and altering behavior might not scale
>> >>> across kernel version and interface changes.
>> >>>
>> >>> But yes, you can technically capture any kernel instruction's virtual
>> >>> address and probe into it. Building solution on top of such
>> >>> instrumentation -- HACK!! :)
>> >> Ok Thanks. I see it will be real slow then as its only a debugging
>> >> mechanism, I also found a hack which uses a kprobe based approach and
>> >> adds a jump code to beginning of system calls. Yes I agree with you ,
>> >> I don't want hack which needs to be changed with kernel versions or
>> >> depends on configuration of kernel.
>> >> I will give a try to wrapfs today. :) Is it too a hack ?
>> >>>
>> >>> Did you try looking for LSM as well?
>> >> LSM projects like SELinux ? Actually they need kernel rebuild/
>> >> reinstall thus I would try not to go for such options.
>> >>>
>> >>> -Rajat
>> >>>
>> >>
>> >> --
>> >> Thanks and Regards ,
>> >> Gaurav
>> >
>>
>>
>> --
>> Thanks and Regards ,
>> Gaurav
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel"
>> in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
> Just to let you know, you can make use of
> http://gauravnaigaonkar.web.officelive.com/Documents/hw2.txt as a reference
> on how to write a stackable file system. This is for linux kernel version
> 2.6.26
>
> Regards,
> Rohan Puri
>


-- 
Thanks and Regards ,
Gaurav