linux-ext4 - Re: [PATCH -V4 08/11] vfs: Add new file and directory create permission flags

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Date:	Sat, 25 Sep 2010 00:46:03 +0530
From:	"Aneesh Kumar K. V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	sfrench@...ibm.com, ffilz@...ibm.com, agruen@...e.de,
	adilger@....com, sandeen@...hat.com, tytso@....edu,
	bfields@...i.umich.edu, linux-fsdevel@...r.kernel.org,
	nfsv4@...ux-nfs.org, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V4 08/11] vfs: Add new file and directory create permission flags

On Fri, 24 Sep 2010 11:54:23 -0400, Jeff Layton <jlayton@...hat.com> wrote:
> On Fri, 24 Sep 2010 18:18:11 +0530
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> wrote:
> 
> > From: Andreas Gruenbacher <agruen@...e.de>
> > 
> > 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@...e.de>
> > 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 b0b8a71..ed786b2 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -253,7 +253,8 @@ int generic_permission(struct inode *inode, int mask,
> >   * 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)
> >  {
> > @@ -1337,13 +1338,15 @@ static int may_delete(struct inode *dir,struct dentry *victim,int 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, int isdir)
> 									^^^^^
> 								nit: maybe saner as a bool?
> >  {
> > +	int mask = isdir ? MAY_CREATE_DIR : MAY_CREATE_FILE;
> > +
> >  	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);
> >  }
> >  
> >  /*
> > @@ -1391,7 +1394,7 @@ void unlock_rename(struct dentry *p1, struct dentry *p2)
> >  int vfs_create(struct inode *dir, struct dentry *dentry, int mode,
> >  		struct nameidata *nd)
> >  {
> > -	int error = may_create(dir, dentry);
> > +	int error = may_create(dir, dentry, 0);
> >  
> >  	if (error)
> >  		return error;
> > @@ -1953,7 +1956,7 @@ EXPORT_SYMBOL_GPL(lookup_create);
> >  
> >  int vfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
> >  {
> > -	int error = may_create(dir, dentry);
> > +	int error = may_create(dir, dentry, 0);
> >  
> >  	if (error)
> >  		return error;
> > @@ -2057,7 +2060,7 @@ SYSCALL_DEFINE3(mknod, const char __user *, filename, int, mode, unsigned, dev)
> >  
> >  int vfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
> >  {
> > -	int error = may_create(dir, dentry);
> > +	int error = may_create(dir, dentry, 1);
> >  
> >  	if (error)
> >  		return error;
> > @@ -2342,7 +2345,7 @@ 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;
> > @@ -2415,7 +2418,7 @@ 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, S_ISDIR(inode->i_mode));
> 
> 						^^^^ this is a little
> 						scary, but even if it's
> 						a directory, it'll get
> 						kicked out in a later
> 						check. Would it be
> 						clearer to move up the
> 						S_ISDIR() check in this
> 						function and then pass
> 						this in as false?

Can you elaborate on this ? 

-aneesh

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