Re: [PATCH -V7 09/26] vfs: Add delete child and delete self permission flags

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On Thu, Oct 20, 2011 at 01:05:26PM +0530, Aneesh Kumar K.V wrote:
> On Wed, 19 Oct 2011 18:09:15 -0400, "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> > Maybe I'm dense, but that big if-else-if is still giving me a headache.
> > 
> > The point is just to delay the ns_capable() check to avoid setting
> > PF_SUPERPRIV in cases where we weren't before?
> > 
> > How about putting using a helper function for the richacl check, and
> > calling it from check_sticky instead? That makes the above:
> > 
> > 	error = inode_permission(dir, mask | replace_mask);
> > 	if (error && !richacl_may_delete(dir, inode, replace_mask))
> > 		return error;
> > 	if (check_sticky(dir, inode, replace_mask))
> > 		return -EPERM;
> > 
> > (As in the following--totally untested and possibly wrong.)
> > 
> > Also: the comment before may_delete() needs updating.
> > 
> 
> Thanks for the suggestion. That made the code simpler. Updated patch
> below.

Looks good to me if it passes your tests, thanks!  Feel free to add
Reviewed-by or Acked-by for "J. Bruce Fields" <bfields@xxxxxxxxxx>.

--b.

> 
> commit 3c92363ce2dee22aa174327c21726f8f02cbcd6e
> Author: Andreas Gruenbacher <agruen@xxxxxxxxxx>
> Date:   Tue Oct 18 15:17:50 2011 +0530
> 
>     vfs: Add delete child and delete self permission flags
>     
>     Normally, deleting a file requires write access to the parent directory.
>     Some permission models use a different permission on the parent
>     directory to indicate delete access.  In addition, a process can have
>     per-file delete access even without delete access on the parent
>     directory.
>     
>     Introduce two new inode_permission() mask flags and use them in
>     may_delete()
>     
>     Acked-by: David Howells <dhowells@xxxxxxxxxx>
>     Signed-off-by: Andreas Gruenbacher <agruen@xxxxxxxxxx>
>     Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index f6184b8..044b6d1 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -337,7 +337,7 @@ static inline int do_inode_permission(struct inode *inode, int mask)
>   * 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)
>  {
> @@ -1835,11 +1835,25 @@ static int user_path_parent(int dfd, const char __user *path,
>  	return error;
>  }
>  
> +
> +/*
> + * We should have exec permission on directory and MAY_DELETE_SELF
> + * on the object being deleted.
> + */
> +static int richacl_may_selfdelete(struct inode *dir,
> +				  struct inode *inode, int replace_mask)
> +{
> +	return (IS_RICHACL(inode) &&
> +		(inode_permission(dir, MAY_EXEC | replace_mask) == 0) &&
> +		(inode_permission(inode, MAY_DELETE_SELF) == 0));
> +}
> +
>  /*
>   * It's inline, so penalty for filesystems that don't use sticky bit is
>   * minimal.
>   */
> -static inline int check_sticky(struct inode *dir, struct inode *inode)
> +static inline int check_sticky(struct inode *dir,
> +			       struct inode *inode, int replace_mask)
>  {
>  	uid_t fsuid = current_fsuid();
>  
> @@ -1851,7 +1865,8 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
>  		return 0;
>  	if (dir->i_uid == fsuid)
>  		return 0;
> -
> +	if (richacl_may_selfdelete(dir, inode, replace_mask))
> +		return 0;
>  other_userns:
>  	return !ns_capable(inode_userns(inode), CAP_FOWNER);
>  }
> @@ -1875,30 +1890,38 @@ other_userns:
>   * 10. We don't allow removal of NFS sillyrenamed files; it's handled by
>   *     nfs_async_unlink().
>   */
> -static int may_delete(struct inode *dir,struct dentry *victim,int isdir)
> +static int may_delete(struct inode *dir, struct dentry *victim,
> +		      int isdir, int replace)
>  {
> -	int error;
> +	int mask, replace_mask = 0, error;
> +	struct inode *inode = victim->d_inode;
>  
> -	if (!victim->d_inode)
> +	if (!inode)
>  		return -ENOENT;
>  
>  	BUG_ON(victim->d_parent->d_inode != dir);
>  	audit_inode_child(victim, dir);
>  
> -	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
> +	mask = MAY_WRITE | MAY_EXEC | MAY_DELETE_CHILD;
> +	if (replace)
> +		replace_mask = S_ISDIR(inode->i_mode) ?
> +				MAY_CREATE_DIR : MAY_CREATE_FILE;
> +	error = inode_permission(dir, mask | replace_mask);
> +	if (error && richacl_may_selfdelete(dir, inode, replace_mask))
> +		error = 0;
>  	if (error)
>  		return error;
>  	if (IS_APPEND(dir))
>  		return -EPERM;
> -	if (check_sticky(dir, victim->d_inode)||IS_APPEND(victim->d_inode)||
> -	    IS_IMMUTABLE(victim->d_inode) || IS_SWAPFILE(victim->d_inode))
> +	if (check_sticky(dir, inode, replace_mask) || IS_APPEND(inode) ||
> +	    IS_IMMUTABLE(inode) || IS_SWAPFILE(inode))
>  		return -EPERM;
>  	if (isdir) {
> -		if (!S_ISDIR(victim->d_inode->i_mode))
> +		if (!S_ISDIR(inode->i_mode))
>  			return -ENOTDIR;
>  		if (IS_ROOT(victim))
>  			return -EBUSY;
> -	} else if (S_ISDIR(victim->d_inode->i_mode))
> +	} else if (S_ISDIR(inode->i_mode))
>  		return -EISDIR;
>  	if (IS_DEADDIR(dir))
>  		return -ENOENT;
> @@ -2605,7 +2628,7 @@ void dentry_unhash(struct dentry *dentry)
>  
>  int vfs_rmdir(struct inode *dir, struct dentry *dentry)
>  {
> -	int error = may_delete(dir, dentry, 1);
> +	int error = may_delete(dir, dentry, 1, 0);
>  
>  	if (error)
>  		return error;
> @@ -2700,7 +2723,7 @@ SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
>  
>  int vfs_unlink(struct inode *dir, struct dentry *dentry)
>  {
> -	int error = may_delete(dir, dentry, 0);
> +	int error = may_delete(dir, dentry, 0, 0);
>  
>  	if (error)
>  		return error;
> @@ -3096,14 +3119,14 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
>  	if (old_dentry->d_inode == new_dentry->d_inode)
>   		return 0;
>   
> -	error = may_delete(old_dir, old_dentry, is_dir);
> +	error = may_delete(old_dir, old_dentry, is_dir, 0);
>  	if (error)
>  		return error;
>  
>  	if (!new_dentry->d_inode)
>  		error = may_create(new_dir, new_dentry, is_dir);
>  	else
> -		error = may_delete(new_dir, new_dentry, is_dir);
> +		error = may_delete(new_dir, new_dentry, is_dir, 1);
>  	if (error)
>  		return error;
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 60361c6..ccece40 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -69,6 +69,8 @@ struct inodes_stat_t {
>  #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
> 
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