Re: [PATCH v23 03/22] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD permission flags

[Jeff Layton]

On Thu, 2016-06-30 at 15:46 +0200, Andreas Gruenbacher wrote:
> Normally, deleting a file requires MAY_WRITE access to the parent
> directory.ÂÂWith richacls, a file may be deleted with MAY_DELETE_CHILD access
> to the parent directory or with MAY_DELETE_SELF access to the file.
> 
> 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.
> 

Minor misspelling in changelog above. It should be "itself".

> The MAY_DELETE_SELF permission overrides the sticky directory check.
> 
> Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
> Reviewed-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> Reviewed-by: Steve French <steve.french@xxxxxxxxxxxxxxx>
> ---
> Âfs/namei.cÂÂÂÂÂÂÂÂÂ| 20 ++++++++++++--------
> Âinclude/linux/fs.h |ÂÂ2 ++
> Â2 files changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index dc91858..663933e 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -454,9 +454,9 @@ static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
> Â * this, letting us set arbitrary permissions for filesystem access without
> Â * changing the "normal" UIDs which are used for other things.
> Â *
> - * MAY_WRITE must be set in @mask whenever MAY_APPEND, MAY_CREATE_FILE, or
> - * MAY_CREATE_DIR are set.ÂÂThat way, file systems that don't support these
> - * permissions will check for MAY_WRITE instead.
> + * MAY_WRITE must be set in @mask whenever MAY_APPEND, MAY_CREATE_FILE,
> + * MAY_CREATE_DIR, or MAY_DELETE_CHILD are set.ÂÂThat way, file systems that
> + * don't support these permissions will check for MAY_WRITE instead.
> Â */
> Âint inode_permission(struct inode *inode, int mask)
> Â{
> @@ -2778,14 +2778,18 @@ static int may_delete_or_replace(struct inode *dir, struct dentry *victim,
> Â	BUG_ON(victim->d_parent->d_inode != dir);
> Â	audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE);
> Â
> -	error = inode_permission(dir, mask);
> +	error = inode_permission(dir, mask | MAY_WRITE | MAY_DELETE_CHILD);
> +	if (!error && check_sticky(dir, inode))
> +		error = -EPERM;
> +	if (error && IS_RICHACL(inode) &&
> +	ÂÂÂÂinode_permission(inode, MAY_DELETE_SELF) == 0 &&
> +	ÂÂÂÂinode_permission(dir, mask) == 0)
> +		error = 0;
> Â	if (error)
> Â		return error;
> Â	if (IS_APPEND(dir))
> Â		return -EPERM;
> -
> -	if (check_sticky(dir, inode) || IS_APPEND(inode) ||
> -	ÂÂÂÂIS_IMMUTABLE(inode) || IS_SWAPFILE(inode))
> +	if (IS_APPEND(inode) || IS_IMMUTABLE(inode) || IS_SWAPFILE(inode))
> Â		return -EPERM;
> Â	if (isdir) {
> Â		if (!d_is_dir(victim))
> @@ -2803,7 +2807,7 @@ static int may_delete_or_replace(struct inode *dir, struct dentry *victim,
> Â
> Âstatic int may_delete(struct inode *dir, struct dentry *victim, bool isdir)
> Â{
> -	return may_delete_or_replace(dir, victim, isdir, MAY_WRITE | MAY_EXEC);
> +	return may_delete_or_replace(dir, victim, isdir, MAY_EXEC);
> Â}
> Â
> Âstatic int may_replace(struct inode *dir, struct dentry *victim, bool isdir)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index dd614ad..86bfa10 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -86,6 +86,8 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
> Â#define MAY_NOT_BLOCK		0x00000080
> Â#define MAY_CREATE_FILE		0x00000100
> Â#define MAY_CREATE_DIR		0x00000200
> +#define MAY_DELETE_CHILD	0x00000400
> +#define MAY_DELETE_SELF		0x00000800
> Â
> Â/*
> Â * flags in file.f_mode.ÂÂNote that FMODE_READ and FMODE_WRITE must correspond

Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>