Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <0000000000006946d2057bbd0eef@google.com> <CAHk-=wiijJMTw=nTj_ED+YWMCrvHzh3ezfVYRxvzcW6+trgyPA@mail.gmail.com>
 <20190325045744.GK2217@ZenIV.linux.org.uk> <CAHk-=wg4iJsMHBzK52WzP+5_92HbwvX_vh_s4mMUuN0FJGdM5A@mail.gmail.com>
 <CAHk-=whJ4M5FegOLvnjUtJ0+pHv4L8UNFt+9jJDhox3Ada8kwA@mail.gmail.com>
 <20190325211405.GP2217@ZenIV.linux.org.uk> <CAHk-=wj+-e=X9cvvNwc5+QuvBOyYT7OtZTBzy-Wg8zGrUwxSbw@mail.gmail.com>
 <20190325233731.GS2217@ZenIV.linux.org.uk> <20190326013858.GU2217@ZenIV.linux.org.uk>
In-Reply-To: <20190326013858.GU2217@ZenIV.linux.org.uk>
From:   Jeff Layton <jlayton@poochiereds.net>
Date:   Tue, 26 Mar 2019 06:41:25 -0400
Message-ID: <CAOhYWNLVMrG_ddvddrbjpAgYKuY+sPtdBk5ja6HFmW2qOeUENA@mail.gmail.com>
Subject: Re: ceph: fix use-after-free on symlink traversal
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        syzbot <syzbot+7a8ba368b47fdefca61e@syzkaller.appspotmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Mar 25, 2019 at 9:39 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> free the symlink body after the same RCU delay we have for freeing the
> struct inode itself, so that traversal during RCU pathwalk wouldn't step
> into freed memory.
>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
> diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
> index e3346628efe2..2d61ddda9bf5 100644
> --- a/fs/ceph/inode.c
> +++ b/fs/ceph/inode.c
> @@ -524,6 +524,7 @@ static void ceph_i_callback(struct rcu_head *head)
>         struct inode *inode = container_of(head, struct inode, i_rcu);
>         struct ceph_inode_info *ci = ceph_inode(inode);
>
> +       kfree(ci->i_symlink);
>         kmem_cache_free(ceph_inode_cachep, ci);
>  }
>
> @@ -566,7 +567,6 @@ void ceph_destroy_inode(struct inode *inode)
>                 }
>         }
>
> -       kfree(ci->i_symlink);
>         while ((n = rb_first(&ci->i_fragtree)) != NULL) {
>                 frag = rb_entry(n, struct ceph_inode_frag, node);
>                 rb_erase(n, &ci->i_fragtree);


Reviewed-by: Jeff Layton <jlayton@kernel.org>