From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B271C77B7A for ; Tue, 30 May 2023 08:26:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230012AbjE3I0K (ORCPT ); Tue, 30 May 2023 04:26:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40312 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229504AbjE3I0J (ORCPT ); Tue, 30 May 2023 04:26:09 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7D06F9D; Tue, 30 May 2023 01:26:07 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 11CC662BC9; Tue, 30 May 2023 08:26:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2EE1EC433D2; Tue, 30 May 2023 08:26:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1685435166; bh=gV7/E8xwGz8n4hz/QHyBLw7IDb3oqSnvYUBNMP6S4TQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=intwRy1xi/TyOKKIj28kVl1c3fBzPeTdM0ZH8LE3yH0DfOpESSMEA7TYMo1w/LINp 3b9wJDjZIFy3D1oe4i4kedf7MYnHRavsHvF03cNPU27JE0z7XE05+dTtNkovfHco2c Ye0eHI8Sf76Dh6lu8JdK+4iQRxCEqdKyvjtD2uCJ52Bgt+64Y4VvLqaScTt6Sjkdsh Ajdt1mOHkzXScmyr4ZdJRDsP9IB/tSRl+IXpRzBpFH/gOHK2BM4X/UN/aUeQfHhwQx Up+RmjKnOpuPoGuib93EtTEOm34U1mkoK3ggUyJgey8BJXYU8t5o3GAaK4nHmgSjkY tbkC09OLGNvEw== Date: Tue, 30 May 2023 10:26:01 +0200 From: Christian Brauner To: Prince Kumar Maurya Cc: skhan@linuxfoundation.org, viro@zeniv.linux.org.uk, chenzhongjin@huawei.com, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linuxfoundation.org, syzkaller-bugs@googlegroups.com, linux-fsdevel@vger.kernel.org, syzbot+aad58150cbc64ba41bdc@syzkaller.appspotmail.com Subject: Re: [PATCH v3] fs/sysv: Null check to prevent null-ptr-deref bug Message-ID: <20230530-zenit-radeln-06417ce5fe85@brauner> References: <000000000000cafb9305fc4fe588@google.com> <20230528184422.596947-1-princekumarmaurya06@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230528184422.596947-1-princekumarmaurya06@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sun, May 28, 2023 at 11:44:22AM -0700, Prince Kumar Maurya wrote: > sb_getblk(inode->i_sb, parent) return a null ptr and taking lock on > that leads to the null-ptr-deref bug. > > Reported-by: syzbot+aad58150cbc64ba41bdc@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=aad58150cbc64ba41bdc > Signed-off-by: Prince Kumar Maurya > --- > Change since v2: Updated subject and added Reported-by and closes tags. > > fs/sysv/itree.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/sysv/itree.c b/fs/sysv/itree.c > index b22764fe669c..3a6b66e719fd 100644 > --- a/fs/sysv/itree.c > +++ b/fs/sysv/itree.c > @@ -145,6 +145,8 @@ static int alloc_branch(struct inode *inode, > */ > parent = block_to_cpu(SYSV_SB(inode->i_sb), branch[n-1].key); > bh = sb_getblk(inode->i_sb, parent); > + if (!bh) > + break; When you break here you'll hit: /* Allocation failed, free what we already allocated */ for (i = 1; i < n; i++) bforget(branch[i].bh); for (i = 0; i < n; i++) sysv_free_block(inode->i_sb, branch[i].key); below. The cleanup paths were coded in the assumption that sb_getblk() can't fail. So bforget() can assume that branch[i].bh has been allocated and set up. So that bforget(branch[i].bh) is your next pending NULL deref afaict.