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    SubjectRe: [PATCH -V6 09/26] vfs: Add delete child and delete self permission flags
    On Thu, Sep 08, 2011 at 03:00:58PM +0530, Aneesh Kumar K.V wrote:
    > On Wed, 7 Sep 2011 16:39:16 -0400, "J. Bruce Fields" <bfields@fieldses.org> wrote:
    > > On Mon, Sep 05, 2011 at 10:55:31PM +0530, Aneesh Kumar K.V wrote:
    > > > From: Andreas Gruenbacher <agruen@kernel.org>
    > > >
    > > > 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()
    > > >
    > > > Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
    > > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    > > > ---
    > > > fs/namei.c | 41 +++++++++++++++++++++++++++--------------
    > > > include/linux/fs.h | 2 ++
    > > > 2 files changed, 29 insertions(+), 14 deletions(-)
    > > >
    > > > diff --git a/fs/namei.c b/fs/namei.c
    > > > index d52a4cd..eacb530 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)
    > > > {
    > > > @@ -1862,7 +1862,7 @@ static inline int check_sticky(struct inode *dir, struct inode *inode)
    > > > return 0;
    > > >
    > > > other_userns:
    > > > - return !ns_capable(inode_userns(inode), CAP_FOWNER);
    > > > + return 1;
    > > > }
    > > >
    > > > /*
    > > > @@ -1884,30 +1884,43 @@ 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, error, is_sticky;
    > > > + 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)
    > > > + mask |= S_ISDIR(inode->i_mode) ?
    > > > + MAY_CREATE_DIR : MAY_CREATE_FILE;
    > >
    > > I'm having trouble understanding this next bit:
    > >
    > > > + is_sticky = check_sticky(dir, inode);
    > > > + error = inode_permission(dir, mask);
    > > > + if ((error || is_sticky) && IS_RICHACL(inode) &&
    > > > + !inode_permission(dir, mask & ~(MAY_WRITE | MAY_DELETE_CHILD)) &&
    > > > + !inode_permission(inode, MAY_DELETE_SELF))
    > > > + error = 0;
    > >
    > > OK, so we can ignore the lack of write or delete permissions on the
    > > parent if we have delete_self permissions on the child. I guess that's
    > > right.
    > >
    > > Why the "|| is_sticky" above?
    > >
    > > Is there some less complicated why to write this?
    >
    > we removed the ns_capable check out of check_sticky, because we don't
    > want to do capability check when richacl allows access. We also want to
    > make sure that even if mode bits allow access (inode_permission(dir, mask))
    > if sticky bit is set we do additional check.

    Why are the two inode_permissions ANDed? The windows semantics are that
    you can delete if you have MAY_DELETE_CHILD *or* MAY_DELETE_SELF.

    --b.


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