Re: [NFS] [PATCH] Bug in NFS

[Abramo Bagnara <abramo@alsa-project.org>]

Neil Brown wrote:
> 
> On Friday July 13, abramo@alsa-project.org wrote:
> >
> > I have found a bug in NFSv2.
> >
> > [root@igor /tmp]# mount igor:/u u
> > [root@igor /tmp]# cd u
> > [root@igor u]# umask 000
> > [root@igor u]# ls -l q
> > ls: q: File o directory inesistente
> > [root@igor u]# touch q
> > [root@igor u]# ls -l q
> > -rw-r--r--    1 root     root            0 lug 13 07:56 q
> >
> > This seems to be caused by use of unitialized current->fs->umask via
> > vfs_create called by nfsd_create.
> >
> 
> Hmmm..  I think there is more here than immediately meets the eye.
> 
> current->fs->umask is initialised, to 0, in include/linux/fs_struct.h
> The "INIT_FS" define is used to set the initial value of the fs_struct
> (see arch/i386/kernel/init_task.c - other archs are the same).
> The third field here is the umask field.
> 
> This is the fs_struct for init, and for every kernel thread that call
> daemonise, as the nfsd threads do ever since 2.4.3pre5 or there abouts.
> 
> If the umask for nfsd is getting set to 022, as it would appear from
> your experiment, then either:
>   - your init process is setting it, or
>   - you are using some odd architecture that doesn't use INIT_FS
> 
> So: what init program are you running, what architecture, any other
> patches, anything else that might explain why your machine is
> different from mine.  Because on mine, the touched file gets the right
> permissions.

I've seen that on several systems with the following characteristics:

- Torvalds linux-2.4.6, Torvalds linux-2.4.4, linux-2.4.4+xfs from sgi
- nfsd compiled as a module (I suppose this make the difference we see)
- stock redhat-7.1 with updates applied

$ rpm -qf /sbin/init
SysVinit-2.78-17

-- 
Abramo Bagnara                       mailto:abramo@alsa-project.org

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It sounds good!