From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <1341597173.5347.5.camel@localhost> Subject: Re: [PATCH 2/3] audit: fix refcounting in audit-tree From: Eric Paris To: Miklos Szeredi Cc: viro@ZenIV.linux.org.uk, linux-kernel@vger.kernel.org, mszeredi@suse.cz, stable@vger.kernel.org Date: Fri, 06 Jul 2012 13:52:53 -0400 In-Reply-To: <1340646378-5169-3-git-send-email-miklos@szeredi.hu> References: <1340646378-5169-1-git-send-email-miklos@szeredi.hu> <1340646378-5169-3-git-send-email-miklos@szeredi.hu> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: On Mon, 2012-06-25 at 19:46 +0200, Miklos Szeredi wrote: > From: Miklos Szeredi > > 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 > 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 Reported-by: Peter Moody Partial-patch-by: Marcelo Cerri Signed-off-by: Eric Paris 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; > } >