linux-kernel - Re: utimes() with vfat is problematic

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Date:	Wed, 11 Jul 2007 13:49:03 +0200
From:	Bodo Eggert <7eggert@....de>
To:	Jan Engelhardt <jengelh@...putergmbh.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	hirofumi@...l.parknet.co.jp, linux-fsdevel@...r.kernel.org
Subject: Re: utimes() with vfat is problematic

Jan Engelhardt <jengelh@...putergmbh.de> wrote:

> vfat does not know about ownership, hence the files are always owned by the
> vfat mounter (or whatever the uid= option specified). Which brings
> a problem to userspace programs trying to utime() but which do not
> run as the same user as the vfat mounter, because:
> 
> 
> fs/attr.c:53
> ret = -EPERM;
> [...]
> 
> /* Check for setting the inode time. */
> if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET)) {
> if (current->fsuid != inode->i_uid && !capable(CAP_FOWNER))
>                         goto error;
>         }
> 
> 
> To trigger the problem:
> # mount /somevfat -o umask=0,uid=root
> $ touch -d "2005-05-05" /somevfat/myfile
> 
> I am not sure how this could be dealt with besides passing -o quiet to
> mount.vfat. Any ideas?

Would it be possible to allow any user to modify the fs by adding
"&& current->fsuid != -1"? I think it's commonly the desired behaviour.
Off cause the default behaviour should stay the same.
-- 
Those who hesitate under fire usually do not end up KIA or WIA. 

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