Re: [PATCH 04/22] fsnotify: Remove fsnotify_duplicate_mark()

[Jan Kara <jack@suse.cz>]

On Thu 22-12-16 18:13:11, Paul Moore wrote:
> On Thu, Dec 22, 2016 at 4:15 AM, Jan Kara <jack@suse.cz> wrote:
> > There are only two calls sites of fsnotify_duplicate_mark(). Those are
> > in kernel/audit_tree.c and both are bogus. Vfsmount pointer is unused
> > for audit tree, inode pointer and group gets set in
> > fsnotify_add_mark_locked() later anyway, mask and free_mark are already
> > set in alloc_chunk(). In fact, calling fsnotify_duplicate_mark() is
> > actively harmful because following fsnotify_add_mark_locked() will leak
> > group reference by overwriting the group pointer. So just remove the two
> > calls to fsnotify_duplicate_mark() and the function.
> >
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> >  fs/notify/mark.c                 | 12 ------------
> >  include/linux/fsnotify_backend.h |  2 --
> >  kernel/audit_tree.c              |  6 ++----
> >  3 files changed, 2 insertions(+), 18 deletions(-)
> 
> At first glance this looks reasonable, although you keep mentioning
> "fsnotify_add_mark_locked" above when untag_chunk() is calling
> "fsnotify_add_mark"; I just wanted to make sure you hadn't intended to
> take the mutex in the audit code instead of relying on the locking in
> fsnotify_add_mark().

No, I didn't want to take mutex in the audit code. It is just that
fsnotify_add_mark() is a thin wrapper around fsnotify_add_mark_locked() so
I was speaking about that function.

								Honza

> 
> > diff --git a/fs/notify/mark.c b/fs/notify/mark.c
> > index d3fea0bd89e2..6043306e8e21 100644
> > --- a/fs/notify/mark.c
> > +++ b/fs/notify/mark.c
> > @@ -510,18 +510,6 @@ void fsnotify_detach_group_marks(struct fsnotify_group *group)
> >         }
> >  }
> >
> > -void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old)
> > -{
> > -       assert_spin_locked(&old->lock);
> > -       new->inode = old->inode;
> > -       new->mnt = old->mnt;
> > -       if (old->group)
> > -               fsnotify_get_group(old->group);
> > -       new->group = old->group;
> > -       new->mask = old->mask;
> > -       new->free_mark = old->free_mark;
> > -}
> > -
> >  /*
> >   * Nothing fancy, just initialize lists and locks and counters.
> >   */
> > diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
> > index 0cf34d6cc253..487246546ebe 100644
> > --- a/include/linux/fsnotify_backend.h
> > +++ b/include/linux/fsnotify_backend.h
> > @@ -323,8 +323,6 @@ extern void fsnotify_init_mark(struct fsnotify_mark *mark, void (*free_mark)(str
> >  extern struct fsnotify_mark *fsnotify_find_inode_mark(struct fsnotify_group *group, struct inode *inode);
> >  /* find (and take a reference) to a mark associated with group and vfsmount */
> >  extern struct fsnotify_mark *fsnotify_find_vfsmount_mark(struct fsnotify_group *group, struct vfsmount *mnt);
> > -/* copy the values from old into new */
> > -extern void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old);
> >  /* set the ignored_mask of a mark */
> >  extern void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask);
> >  /* set the mask of a mark (might pin the object into memory */
> > diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> > index 8b1dde96a0fa..f3130eb0a4bd 100644
> > --- a/kernel/audit_tree.c
> > +++ b/kernel/audit_tree.c
> > @@ -258,8 +258,7 @@ static void untag_chunk(struct node *p)
> >         if (!new)
> >                 goto Fallback;
> >
> > -       fsnotify_duplicate_mark(&new->mark, entry);
> > -       if (fsnotify_add_mark(&new->mark, new->mark.group, new->mark.inode, NULL, 1)) {
> > +       if (fsnotify_add_mark(&new->mark, entry->group, entry->inode, NULL, 1)) {
> >                 fsnotify_put_mark(&new->mark);
> >                 goto Fallback;
> >         }
> > @@ -395,8 +394,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree)
> >                 return -ENOENT;
> >         }
> >
> > -       fsnotify_duplicate_mark(chunk_entry, old_entry);
> > -       if (fsnotify_add_mark(chunk_entry, chunk_entry->group, chunk_entry->inode, NULL, 1)) {
> > +       if (fsnotify_add_mark(chunk_entry, old_entry->group, old_entry->inode, NULL, 1)) {
> >                 spin_unlock(&old_entry->lock);
> >                 fsnotify_put_mark(chunk_entry);
> >                 fsnotify_put_mark(old_entry);
> > --
> > 2.10.2
> >
> 
> -- 
> paul moore
> www.paul-moore.com
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR