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

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On Thu, Dec 22, 2016 at 4:15 AM, Jan Kara <jack@xxxxxxx> 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@xxxxxxx>
> ---
>  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().

> 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
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