Re: [PATCH v23 02/22] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags

[Jeff Layton <jlayton@redhat.com>]

On Thu, 2016-06-30 at 15:46 +0200, Andreas Gruenbacher wrote:
> Richacls distinguish between creating non-directories and directories. To
> support that, add an isdir parameter to may_create(). When checking
> inode_permission() for create permission, pass in an additional
> MAY_CREATE_FILE or MAY_CREATE_DIR mask flag.
> 
> Add may_replace() to allow checking for delete and create access when
> replacing an existing file in vfs_rename().
> 
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> Reviewed-by: J. Bruce Fields <bfields@redhat.com>
> Reviewed-by: Andreas Dilger <adilger@dilger.ca>
> Reviewed-by: Steve French <steve.french@primarydata.com>
> ---
>  fs/namei.c         | 49 +++++++++++++++++++++++++++++++++----------------
>  include/linux/fs.h |  2 ++
>  2 files changed, 35 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 7cc5487..dc91858 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -454,7 +454,9 @@ static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
>   * this, letting us set arbitrary permissions for filesystem access without
>   * changing the "normal" UIDs which are used for other things.
>   *
> - * When checking for MAY_APPEND, MAY_WRITE must also be set in @mask.
> + * MAY_WRITE must be set in @mask whenever MAY_APPEND, MAY_CREATE_FILE, or
> + * MAY_CREATE_DIR are set.  That way, file systems that don't support these
> + * permissions will check for MAY_WRITE instead.
>   */
>  int inode_permission(struct inode *inode, int mask)
>  {
> @@ -2763,7 +2765,8 @@ EXPORT_SYMBOL(__check_sticky);
>   * 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, bool isdir)
> +static int may_delete_or_replace(struct inode *dir, struct dentry *victim,
> +				 bool isdir, int mask)
>  {
>  	struct inode *inode = d_backing_inode(victim);
>  	int error;
> @@ -2775,7 +2778,7 @@ static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
>  	BUG_ON(victim->d_parent->d_inode != dir);
>  	audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);
>  
> -	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
> +	error = inode_permission(dir, mask);
>  	if (error)
>  		return error;
>  	if (IS_APPEND(dir))
> @@ -2798,6 +2801,18 @@ static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
>  	return 0;
>  }
>  
> +static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
> +{
> +	return may_delete_or_replace(dir, victim, isdir, MAY_WRITE | MAY_EXEC);
> +}
> +
> +static int may_replace(struct inode *dir, struct dentry *victim, bool isdir)
> +{
> +	int mask = isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE;
> +
> +	return may_delete_or_replace(dir, victim, isdir, mask | MAY_WRITE | MAY_EXEC);
> +}
> +
>  /*	Check whether we can create an object with dentry child in directory
>   *  dir.
>   *  1. We can't do it if child already exists (open has special treatment for
> @@ -2806,14 +2821,16 @@ static int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
>   *  3. We should have write and exec permissions on dir
>   *  4. We can't do it if dir is immutable (done in permission())
>   */
> -static inline int may_create(struct inode *dir, struct dentry *child)
> +static inline int may_create(struct inode *dir, struct dentry *child, bool isdir)
>  {
> +	int mask = isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE;
> +
>  	audit_inode_child(dir, child, AUDIT_TYPE_CHILD_CREATE);
>  	if (child->d_inode)
>  		return -EEXIST;
>  	if (IS_DEADDIR(dir))
>  		return -ENOENT;
> -	return inode_permission(dir, MAY_WRITE | MAY_EXEC);
> +	return inode_permission(dir, MAY_WRITE | MAY_EXEC | mask);
>  }
>  
>  /*
> @@ -2863,7 +2880,7 @@ EXPORT_SYMBOL(unlock_rename);
>  int vfs_create(struct inode *dir, struct dentry *dentry, umode_t mode,
>  		bool want_excl)
>  {
> -	int error = may_create(dir, dentry);
> +	int error = may_create(dir, dentry, false);
>  	if (error)
>  		return error;
>  
> @@ -3650,7 +3667,7 @@ EXPORT_SYMBOL(user_path_create);
>  
>  int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
>  {
> -	int error = may_create(dir, dentry);
> +	int error = may_create(dir, dentry, false);
>  
>  	if (error)
>  		return error;
> @@ -3744,7 +3761,7 @@ SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, d
>  
>  int vfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
>  {
> -	int error = may_create(dir, dentry);
> +	int error = may_create(dir, dentry, true);
>  	unsigned max_links = dir->i_sb->s_max_links;
>  
>  	if (error)
> @@ -3800,7 +3817,7 @@ SYSCALL_DEFINE2(mkdir, const char __user *, pathname, umode_t, mode)
>  
>  int vfs_rmdir(struct inode *dir, struct dentry *dentry)
>  {
> -	int error = may_delete(dir, dentry, 1);
> +	int error = may_delete(dir, dentry, true);
>  
>  	if (error)
>  		return error;
> @@ -3922,7 +3939,7 @@ SYSCALL_DEFINE1(rmdir, const char __user *, pathname)
>  int vfs_unlink(struct inode *dir, struct dentry *dentry, struct inode **delegated_inode)
>  {
>  	struct inode *target = dentry->d_inode;
> -	int error = may_delete(dir, dentry, 0);
> +	int error = may_delete(dir, dentry, false);
>  
>  	if (error)
>  		return error;
> @@ -4056,7 +4073,7 @@ SYSCALL_DEFINE1(unlink, const char __user *, pathname)
>  
>  int vfs_symlink(struct inode *dir, struct dentry *dentry, const char *oldname)
>  {
> -	int error = may_create(dir, dentry);
> +	int error = may_create(dir, dentry, false);
>  
>  	if (error)
>  		return error;
> @@ -4139,7 +4156,7 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
>  	if (!inode)
>  		return -ENOENT;
>  
> -	error = may_create(dir, new_dentry);
> +	error = may_create(dir, new_dentry, false);
>  	if (error)
>  		return error;
>  
> @@ -4336,14 +4353,14 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
>  		return error;
>  
>  	if (!target) {
> -		error = may_create(new_dir, new_dentry);
> +		error = may_create(new_dir, new_dentry, is_dir);
>  	} else {
>  		new_is_dir = d_is_dir(new_dentry);
>  
>  		if (!(flags & RENAME_EXCHANGE))
> -			error = may_delete(new_dir, new_dentry, is_dir);
> +			error = may_replace(new_dir, new_dentry, is_dir);
>  		else
> -			error = may_delete(new_dir, new_dentry, new_is_dir);
> +			error = may_replace(new_dir, new_dentry, new_is_dir);
>  	}
>  	if (error)
>  		return error;
> @@ -4606,7 +4623,7 @@ SYSCALL_DEFINE2(rename, const char __user *, oldname, const char __user *, newna
>  
>  int vfs_whiteout(struct inode *dir, struct dentry *dentry)
>  {
> -	int error = may_create(dir, dentry);
> +	int error = may_create(dir, dentry, false);
>  	if (error)
>  		return error;
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 4ad130c..dd614ad 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -84,6 +84,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
>  #define MAY_CHDIR		0x00000040
>  /* called from RCU mode, don't block */
>  #define MAY_NOT_BLOCK		0x00000080
> +#define MAY_CREATE_FILE		0x00000100
> +#define MAY_CREATE_DIR		0x00000200
>  
>  /*
>   * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond

Reviewed-by: Jeff Layton <jlayton@redhat.com>