valgrind and fuse file systems

[Kendy Kutzner]

Hello List,

I want to debug my file system and want to use valgrind or similar
tools to do that. However, that bails out with the error message
"fuse: failed to exec fusermount: Permission denied"
Ok, calling setuid-binaries from traced programs is problematic.

However, 'sudo valgrind ./my_file_system' gives the same error
message. Same for a real root shell with su -

Any hints on how to use valgrind like programs with fuse file systems?

Kendy

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[Patrick Eaton-2]

Kendy,

Yes, it is a bit problematic to use Valgrind with a Fuse file system.
Below is a short memo I wrote when I was asked to describe how to use
Valgrind with my Fuse-based FS.  Hopefully it helps you too.

cheers-
patrick


Debugging with Valgrind

Problem

By default, Fuse and Valgrind do not play nice together, making
debugging memory errors in the <myfs> a bit of a hassle.

See the links below for a little bit of background.

>From http://thread.gmane.org/gmane.comp.file-systems.fuse.devel/4095/focus=4114
(note, Miklos is the developer of Fuse).

>> [*] I had been having problems with valgrind and permission problems.
>> What works is to run valgrind as root, and chmod 755
>> /usr/bin/fusermount.
>
>Yes, stupid valgrind.  My workaround is to replace /usr/bin/fusermount
>with a shell script which just execs /usr/bin/fusermount.real.
>Miklos

Also, from http://osdir.com/ml/file-systems.fuse.devel/2006-01/msg00093.html,
it appears the problem is related to setuid programs. The Fuse mount
utility, fusermount, is a setuid program.

Finally, a link in the previous message
http://bugs.kde.org/show_bug.cgi?id=119404 further explains that
setuid programs can be run by valgrind, but they cannot be traced.

Solution

Here is one possible workaround the problem.

As root,

 $ cd /usr/bin
 $ if [[ -e fusermount ]]; then mv fusermount fusermount.real; fi
 $ touch fusermount
 $ chown root.fuse fusermount
 $ chmod ug+x fusermount
 $ echo '#!/bin/sh' >> fusermount
 $ echo 'exec /usr/bin/fusermount.real $@' >> fusermount
 or depending on the path of fusermount
 $ echo 'exec /bin/fusermount $@' >> fusermount

The other key point is to ensure that the setuid fusermount is not
traced. Thus valgrind should be called as

$ valgrind --tool=memcheck --trace-children=no ... myprog ...

One set of valgrind options that may be useful is

$ valgrind --tool=memcheck --trace-children=no --leak-check=full
--show-reachable=yes --max-stackframe=3000000 -v ./myfs ...




On 10/9/07, Kendy Kutzner <kutzner@...> wrote:

> Hello List,
>
> I want to debug my file system and want to use valgrind or similar
> tools to do that. However, that bails out with the error message
> "fuse: failed to exec fusermount: Permission denied"
> Ok, calling setuid-binaries from traced programs is problematic.
>
> However, 'sudo valgrind ./my_file_system' gives the same error
> message. Same for a real root shell with su -
>
> Any hints on how to use valgrind like programs with fuse file systems?
>
> Kendy
>
> --
>
>
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> This SF.net email is sponsored by: Splunk Inc.
> Still grepping through log files to find problems?  Stop.
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> _______________________________________________
> fuse-devel mailing list
> fuse-devel@...
> https://lists.sourceforge.net/lists/listinfo/fuse-devel
>
>
>

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[Kendy Kutzner]

Patrick,

On 2007-10-09T12:43:06-0400, Patrick Eaton wrote:
> Below is a short memo I wrote when I was asked to describe how to use
> Valgrind with my Fuse-based FS.  Hopefully it helps you too.

Yes, it did. Thank you.

Kendy

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