linux-kernel - Re: [RFC v6 03/40] vfs: Add MAY_DELETE_SELF and MAY_DELETE

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Date:	Fri, 28 Aug 2015 16:44:13 -0400
From:	bfields@...ldses.org (J. Bruce Fields)
To:	Andreas Gruenbacher <andreas.gruenbacher@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-nfs@...r.kernel.org, linux-api@...r.kernel.org,
	linux-cifs@...r.kernel.org, linux-security-module@...r.kernel.org,
	Andreas Gruenbacher <agruenba@...hat.com>
Subject: Re: [RFC v6 03/40] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD
 permission flags

On Tue, Aug 04, 2015 at 01:53:01PM +0200, Andreas Gruenbacher wrote:
> Normally, deleting a file requires write and execute access to the parent
> directory.  With Richacls, a process with MAY_DELETE_SELF access to a file
> may delete the file even without write access to the parent directory.
> 
> To support that, pass the MAY_DELETE_CHILD mask flag to inode_permission()
> when checking for delete access inside a directory, and MAY_DELETE_SELF
> when checking for delete access to a file itelf.
> 
> The MAY_DELETE_SELF permission does not override the sticky directory
> check.  It probably should.

I guess it would basically just let the file owner delegate permission
to delete your file to a non-owner?  Makes sense to me to allow that.

--b.

> 
> Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
> ---
>  fs/namei.c         | 15 +++++++++++----
>  include/linux/fs.h |  2 ++
>  2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 3504d36..2ac759c 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -454,7 +454,7 @@ static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
>   * changing the "normal" UIDs which are used for other things.
>   *
>   * When checking for MAY_APPEND, MAY_CREATE_FILE, MAY_CREATE_DIR,
> - * MAY_WRITE must also be set in @mask.
> + * MAY_DELETE_CHILD, MAY_DELETE_SELF, MAY_WRITE must also be set in @mask.
>   */
>  int inode_permission(struct inode *inode, int mask)
>  {
> @@ -2527,7 +2527,7 @@ static int may_delete(struct inode *dir, struct dentry *victim,
>  		      bool isdir, bool replace)
>  {
>  	struct inode *inode = d_backing_inode(victim);
> -	int error, mask = MAY_WRITE | MAY_EXEC;
> +	int error, mask = MAY_EXEC;
>  
>  	if (d_is_negative(victim))
>  		return -ENOENT;
> @@ -2537,8 +2537,15 @@ static int may_delete(struct inode *dir, struct dentry *victim,
>  	audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);
>  
>  	if (replace)
> -		mask |= isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE;
> -	error = inode_permission(dir, mask);
> +		mask |= MAY_WRITE | (isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE);
> +	error = inode_permission(dir, mask | MAY_WRITE | MAY_DELETE_CHILD);
> +	if (error && IS_RICHACL(inode)) {
> +		/* Deleting is also permitted with MAY_EXEC on the directory
> +		 * and MAY_DELETE_SELF on the inode.  */
> +		if (!inode_permission(inode, MAY_DELETE_SELF) &&
> +		    !inode_permission(dir, mask))
> +			error = 0;
> +	}
>  	if (error)
>  		return error;
>  	if (IS_APPEND(dir))
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 9c44f27..abf5b0e 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -83,6 +83,8 @@ typedef void (dax_iodone_t)(struct buffer_head *bh_map, int uptodate);
>  #define MAY_NOT_BLOCK		0x00000080
>  #define MAY_CREATE_FILE		0x00000100
>  #define MAY_CREATE_DIR		0x00000200
> +#define MAY_DELETE_CHILD	0x00000400
> +#define MAY_DELETE_SELF		0x00000800
>  
>  /*
>   * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond
> -- 
> 2.5.0
> 
> --
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