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SubjectRe: [PATCH -V6 09/26] vfs: Add delete child and delete self permission flags
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On Fri, 09 Sep 2011 10:49:19 +0530, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
> On Thu, 8 Sep 2011 18:02:46 -0400, "J. Bruce Fields" <bfields@fieldses.org> wrote:
> > On Thu, Sep 08, 2011 at 04:07:54PM -0400, J. Bruce Fields wrote:
> > > 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:
> > > > > > +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.
> >
> > Either way, those conditions are just really hard to follow. Could you
> > simplify the logic, add comments, maybe move the richacl stuff into a
> > little helper function?
> >
> > Also, a nit:
> >
> > > > > > + !inode_permission(dir, mask & ~(MAY_WRITE | MAY_DELETE_CHILD)) &&
> >
> > The way you calculated mask above it always includes MAY_WRITE and
> > MAY_DELETE_CHILD, so the above is equivalent to just
> >
> > !inode_permission(dir, MAY_WRITE | MAY_DELETE_CHILD) &&
> >
> > isn't it?
> >
>
> I guess i can simplify it as
> !inode_permission(dir, MAY_EXEC | replace_mask)
>

diff --git a/fs/namei.c b/fs/namei.c
index 1054bc3..e545c81 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1912,8 +1912,9 @@ other_userns:
static int may_delete(struct inode *dir, struct dentry *victim,
int isdir, int replace)
{
- int mask, error, is_sticky;
struct inode *inode = victim->d_inode;
+ int mask, replace_mask = 0, error, is_sticky;
+

if (!inode)
return -ENOENT;
@@ -1923,12 +1924,12 @@ static int may_delete(struct inode *dir, struct dentry *victim,

mask = MAY_WRITE | MAY_EXEC | MAY_DELETE_CHILD;
if (replace)
- mask |= S_ISDIR(inode->i_mode) ?
- MAY_CREATE_DIR : MAY_CREATE_FILE;
+ replace_mask = S_ISDIR(inode->i_mode) ?
+ MAY_CREATE_DIR : MAY_CREATE_FILE;
is_sticky = check_sticky(dir, inode);
- error = inode_permission(dir, mask);
+ error = inode_permission(dir, mask | replace_mask);
if ((error || is_sticky) && IS_RICHACL(inode) &&
- !inode_permission(dir, mask & ~(MAY_WRITE | MAY_DELETE_CHILD)) &&
+ !inode_permission(dir, MAY_EXEC | replace_mask) &&
!inode_permission(inode, MAY_DELETE_SELF))
error = 0;
else if (!error && is_sticky &&


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