Re: [PATCH 2/2] vfs: show unreachable paths in getcwd and proc

[Miklos Szeredi]

Hi Al,

Could you please consider these patches for 2.6.36?

Thanks,
Miklos


On Fri, 04 Jun 2010, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@xxxxxxx>
> 
> Prepend "(unreachable)" to path strings if the path is not reachable
> from the current root.
> 
> Two places updated are
>  - the return string from getcwd()
>  - and symlinks under /proc/$PID.
> 
> Other uses of d_path() are left unchanged (we know that some old
> software crashes if /proc/mounts is changed).
> 
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
> ---
>  fs/dcache.c            |   82 +++++++++++++++++++++++++++++++++++++++++--------
>  fs/proc/base.c         |    2 -
>  include/linux/dcache.h |    1 
>  3 files changed, 72 insertions(+), 13 deletions(-)
> 
> Index: linux-2.6/fs/dcache.c
> ===================================================================
> --- linux-2.6.orig/fs/dcache.c	2010-05-27 12:22:21.000000000 +0200
> +++ linux-2.6/fs/dcache.c	2010-05-27 12:22:24.000000000 +0200
> @@ -1957,6 +1957,33 @@ int __d_path(const struct path *path, st
>  	return error;
>  }
>  
> +static void current_root(struct path *root)
> +{
> +	read_lock(&current->fs->lock);
> +	*root = current->fs->root;
> +	path_get(root);
> +	read_unlock(&current->fs->lock);
> +}
> +
> +static int __d_path_with_deleted(const struct path *path, struct path *root,
> +				 char **buffer, int *buflen)
> +{
> +	int error;
> +
> +	prepend(buffer, buflen, "\0", 1);
> +	if (d_unlinked(path->dentry)) {
> +		error = prepend(buffer, buflen, " (deleted)", 10);
> +		if (error)
> +			return error;
> +	}
> +	return __d_path(path, root, buffer, buflen);
> +}
> +
> +static int prepend_unreachable(char **buffer, int *buflen)
> +{
> +	return prepend(buffer, buflen, "(unreachable)", 13);
> +}
> +
>  /**
>   * d_path - return the path of a dentry
>   * @path: path to report
> @@ -1990,27 +2017,51 @@ char *d_path(const struct path *path, ch
>  	if (path->dentry->d_op && path->dentry->d_op->d_dname)
>  		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
>  
> -	read_lock(&current->fs->lock);
> -	root = current->fs->root;
> -	path_get(&root);
> -	read_unlock(&current->fs->lock);
> +	current_root(&root);
>  	spin_lock(&dcache_lock);
>  	ptr = buf + buflen;
> -	prepend(&ptr, &buflen, "\0", 1);
> -	if (d_unlinked(path->dentry)) {
> -		error = prepend(&ptr, &buflen, " (deleted)", 10);
> -		if (error)
> -			goto out;
> -	}
>  	tmp = root;
> -	error = __d_path(path, &tmp, &ptr, &buflen);
> -out:
> +	error = __d_path_with_deleted(path, &tmp, &ptr, &buflen);
>  	spin_unlock(&dcache_lock);
>  	path_put(&root);
>  	return error ? ERR_PTR(error) : ptr;
>  }
>  EXPORT_SYMBOL(d_path);
>  
> +/**
> + * d_path_with_unreachable - return the path of a dentry
> + * @path: path to report
> + * @buf: buffer to return value in
> + * @buflen: buffer length
> + *
> + * The difference from d_path() is that this prepends "(unreachable)"
> + * to paths which are unreachable from the current process' root.
> + */
> +char *d_path_with_unreachable(const struct path *path, char *buf, int buflen)
> +{
> +	char *ptr;
> +	struct path root;
> +	struct path tmp;
> +	int error;
> +
> +	if (path->dentry->d_op && path->dentry->d_op->d_dname)
> +		return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
> +
> +	current_root(&root);
> +	spin_lock(&dcache_lock);
> +	ptr = buf + buflen;
> +	tmp = root;
> +	error = __d_path_with_deleted(path, &tmp, &ptr, &buflen);
> +	if (!error) {
> +		if (tmp.dentry != root.dentry || tmp.mnt != root.mnt)
> +			error = prepend_unreachable(&ptr, &buflen);
> +	}
> +
> +	spin_unlock(&dcache_lock);
> +	path_put(&root);
> +	return error ? ERR_PTR(error) : ptr;
> +}
> +
>  /*
>   * Helper function for dentry_operations.d_dname() members
>   */
> @@ -2118,6 +2169,13 @@ SYSCALL_DEFINE2(getcwd, char __user *, b
>  		if (error)
>  			goto out;
>  
> +		/* Unreachable from current root */
> +		if (tmp.dentry != root.dentry || tmp.mnt != root.mnt) {
> +			error = prepend_unreachable(&cwd, &buflen);
> +			if (error)
> +				goto out;
> +		}
> +
>  		error = -ERANGE;
>  		len = PAGE_SIZE + page - cwd;
>  		if (len <= size) {
> Index: linux-2.6/include/linux/dcache.h
> ===================================================================
> --- linux-2.6.orig/include/linux/dcache.h	2010-05-27 12:13:48.000000000 +0200
> +++ linux-2.6/include/linux/dcache.h	2010-05-27 12:22:24.000000000 +0200
> @@ -315,6 +315,7 @@ extern char *dynamic_dname(struct dentry
>  
>  extern int __d_path(const struct path *path, struct path *root, char **, int *);
>  extern char *d_path(const struct path *, char *, int);
> +extern char *d_path_with_unreachable(const struct path *, char *, int);
>  extern char *dentry_path(struct dentry *, char *, int);
>  
>  /* Allocation counts.. */
> Index: linux-2.6/fs/proc/base.c
> ===================================================================
> --- linux-2.6.orig/fs/proc/base.c	2010-05-27 11:53:55.000000000 +0200
> +++ linux-2.6/fs/proc/base.c	2010-05-27 12:22:24.000000000 +0200
> @@ -1438,7 +1438,7 @@ static int do_proc_readlink(struct path
>  	if (!tmp)
>  		return -ENOMEM;
>  
> -	pathname = d_path(path, tmp, PAGE_SIZE);
> +	pathname = d_path_with_unreachable(path, tmp, PAGE_SIZE);
>  	len = PTR_ERR(pathname);
>  	if (IS_ERR(pathname))
>  		goto out;
> 
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