linux-kernel - Re: [PATCH -V1 05/22] vfs: Add new file and directory create permission flags

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Date:	Mon, 28 Apr 2014 07:23:01 -0400
From:	Jeff Layton <jlayton@...chiereds.net>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	agruen@...nel.org, bfields@...ldses.org, akpm@...ux-foundation.org,
	viro@...iv.linux.org.uk, dhowells@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V1 05/22] vfs: Add new file and directory create
 permission flags

On Sun, 27 Apr 2014 21:44:36 +0530
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:

> From: Andreas Gruenbacher <agruen@...nel.org>
> 
> Some permission models distinguish between the permission to create a
> non-directory and a directory.  Pass this information down to
> inode_permission() as mask flags
> 
> Signed-off-by: Andreas Gruenbacher <agruen@...nel.org>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> ---
>  fs/namei.c         | 21 ++++++++++++---------
>  include/linux/fs.h |  2 ++
>  2 files changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 7d93d195f0e5..028bc8bcf77c 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -445,7 +445,8 @@ 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.
> + * When checking for MAY_APPEND, MAY_CREATE_FILE, MAY_CREATE_DIR,
> + * MAY_WRITE must also be set in @mask.
>   */
>  int inode_permission(struct inode *inode, int mask)
>  {
> @@ -2444,14 +2445,16 @@ 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);
>  }
>  
>  /*
> @@ -2501,7 +2504,7 @@ 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, 0);

nit: since the third argument here is a bool, this should be "false"
and not "0". Ditto for all of the other calls of may_create.

>  	if (error)
>  		return error;
>  
> @@ -3363,7 +3366,7 @@ 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, 0);
>  
>  	if (error)
>  		return error;
> @@ -3455,7 +3458,7 @@ 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, 1);
>  	unsigned max_links = dir->i_sb->s_max_links;
>  
>  	if (error)
> @@ -3785,7 +3788,7 @@ 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, 0);
>  
>  	if (error)
>  		return error;
> @@ -3871,7 +3874,7 @@ int vfs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_de
>  	if (S_ISDIR(inode->i_mode))
>  		return -EPERM;
>  
> -	error = may_create(dir, new_dentry);
> +	error = may_create(dir, new_dentry, 0);
>  	if (error)
>  		return error;
>  
> @@ -4062,7 +4065,7 @@ 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);
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 1f524b4b652d..da5521de04ab 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -77,6 +77,8 @@ typedef void (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


-- 
Jeff Layton <jlayton@...chiereds.net>
--
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