linux-kernel - Re: [patch 3/3] vfs: fix sys

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Message-Id: <E1KApHx-0007o1-Td@pomaz-ex.szeredi.hu>
Date:	Mon, 23 Jun 2008 18:53:09 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	viro@...IV.linux.org.uk
CC:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	hch@...radead.org
Subject: Re: [patch 3/3] vfs: fix sys_getcwd for detached mounts

> From: Miklos Szeredi <mszeredi@...e.cz>
> 
> Currently getcwd(2) on a detached mount will give a garbled result:
> 
>    > mkdir /mnt/foo
>    > mount --bind /etc /mnt/foo
>    > cd /mnt/foo/skel
>    > /bin/pwd
>    /mnt/foo/skel
>    > umount -l /mnt/foo
>    > /bin/pwd
>    etcskel
> 
> After the patch it will give "detached:skel" as result.
> 
> Thanks to John Johansen for pointing out this bug.
> 
> Comment from Al Viro: use "detached:" prefix to differentiate it from
> attached paths.
> 
> Reported-by: John Johansen <jjohansen@...e.de>
> Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
> ---
>  fs/dcache.c |   12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/fs/dcache.c
> ===================================================================
> --- linux-2.6.orig/fs/dcache.c	2008-06-23 17:35:39.000000000 +0200
> +++ linux-2.6/fs/dcache.c	2008-06-23 17:46:05.000000000 +0200
> @@ -1828,8 +1828,16 @@ char *__d_path(const struct path *path, 
>  
>  global_root:
>  	retval += 1;	/* hit the slash */
> -	if (prepend_name(&retval, &buflen, &dentry->d_name) != 0)
> -		goto Elong;
> +
> +	if (IS_ROOT(dentry)) {
> +		/* Attached, or pseudo filesystem with "foo:" prefix */
> +		if (prepend_name(&retval, &buflen, &dentry->d_name) != 0)
> +			goto Elong;
> +	} else {
> +		/* Detached */
> +		if (prepend(&retval, &buflen, "detached:", 9) != 0)
> +			goto Elong;
> +	}
>  	root->mnt = vfsmnt;
>  	root->dentry = dentry;
>  	return retval;
> 
> --
> 

Darn, this is wrong.  It should be looking at vfsmnt->mnt_namespace ==
NULL.

Fixed patch coming up.

Miklos
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