Messages in this thread | | | Subject | Re: [PATCH 2/3] audit: fix refcounting in audit-tree | From | Eric Paris <> | Date | Fri, 06 Jul 2012 13:52:53 -0400 |
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On Mon, 2012-06-25 at 19:46 +0200, Miklos Szeredi wrote: > From: Miklos Szeredi <mszeredi@suse.cz> > > Refcounting of fsnotify_mark in audit tree is broken. E.g: > > refcount > create_chunk > alloc_chunk 1 > fsnotify_add_mark 2 > > untag_chunk > fsnotify_get_mark 3 > fsnotify_destroy_mark > audit_tree_freeing_mark 2 > fsnotify_put_mark 1 > fsnotify_put_mark 0 > via destroy_list > fsnotify_mark_destroy -1 > > This was reported by various people as triggering Oops when stopping auditd. > > We could just remove the put_mark from audit_tree_freeing_mark() but that would > break freeing via inode destruction. So this patch simply omits a put_mark > after calling destroy_mark (or adds a get_mark before). > > Next patch will clean up the remaining mess. > > Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> > CC: stable@vger.kernel.org
Agreed this is needed. My changelog was:
audit: fix ref count problems in audit trees
Before the switch from in kernel inotify to fsnotify for audit trees the code regularly did: inotify_evict_watch(&chunk->watch); put_inotify_watch(&chunk->watch);
I translated this in fsnotify_speak into: fsnotify_destroy_mark_by_entry(chunk_entry); fsnotify_put_mark(chunk_entry);
The problem is that the inotify_evict_watch function actually took a reference on chunk->watch, which is what was being dropped by put_inotify_watch(). The fsnotify code does not take such a reference during fsnotify_destroy_mark_by_entry(). Thus we are dropping reference counts prematurely and eventually we hit a use after free! Whoops!
Fix these call sites to not drop the extra reference.
Reported-by: Valentin Avram <aval13@gmail.com> Reported-by: Peter Moody <pmoody@google.com> Partial-patch-by: Marcelo Cerri <mhcerri@linux.vnet.ibm.com> Signed-off-by: Eric Paris <eparis@redhat.com>
Maybe you can use some of that changelog in your next post? (If you do one?) The only reason you would repost is because I don't understand why you took a ref in some places instead of just not dropping it everywhere...
> --- > kernel/audit_tree.c | 5 ++--- > 1 files changed, 2 insertions(+), 3 deletions(-) > > diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c > index d52d247..31fdc48 100644 > --- a/kernel/audit_tree.c > +++ b/kernel/audit_tree.c > @@ -250,7 +250,6 @@ static void untag_chunk(struct node *p) > spin_unlock(&hash_lock); > spin_unlock(&entry->lock); > fsnotify_destroy_mark(entry); > - fsnotify_put_mark(entry); > goto out; > } > > @@ -293,7 +292,6 @@ static void untag_chunk(struct node *p) > spin_unlock(&hash_lock); > spin_unlock(&entry->lock); > fsnotify_destroy_mark(entry); > - fsnotify_put_mark(entry); > goto out; > > Fallback: > @@ -332,6 +330,7 @@ static int create_chunk(struct inode *inode, struct audit_tree *tree) > spin_unlock(&hash_lock); > chunk->dead = 1; > spin_unlock(&entry->lock); > + fsnotify_get_mark(entry); > fsnotify_destroy_mark(entry); > fsnotify_put_mark(entry); > return 0;
Like here? Why not just avoid the atomic op altogether?
> @@ -412,6 +411,7 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree) > spin_unlock(&chunk_entry->lock); > spin_unlock(&old_entry->lock); > > + fsnotify_get_mark(chunk_entry); > fsnotify_destroy_mark(chunk_entry); > > fsnotify_put_mark(chunk_entry); > @@ -445,7 +445,6 @@ static int tag_chunk(struct inode *inode, struct audit_tree *tree) > spin_unlock(&old_entry->lock); > fsnotify_destroy_mark(old_entry); > fsnotify_put_mark(old_entry); /* pair to fsnotify_find mark_entry */ > - fsnotify_put_mark(old_entry); /* and kill it */ > return 0; > } >
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