From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: MIME-Version: 1.0 In-Reply-To: References: <1526379972-20923-1-git-send-email-amir73il@gmail.com> <1526379972-20923-2-git-send-email-amir73il@gmail.com> <20180515132328.GA11678@redhat.com> From: Miklos Szeredi Date: Wed, 16 May 2018 12:14:58 +0200 Message-ID: Subject: Re: [PATCH v3 1/4] ovl: use insert_inode_locked4() to hash a newly created inode To: Amir Goldstein Cc: Vivek Goyal , Al Viro , overlayfs , linux-fsdevel , "#v4 . 16" Content-Type: text/plain; charset="UTF-8" Sender: stable-owner@vger.kernel.org List-ID: On Wed, May 16, 2018 at 11:51 AM, Amir Goldstein wrote: > On Wed, May 16, 2018 at 11:34 AM, Miklos Szeredi wrote: >> On Tue, May 15, 2018 at 3:37 PM, Amir Goldstein wrote: >>> On Tue, May 15, 2018 at 4:23 PM, Vivek Goyal wrote: >>>> On Tue, May 15, 2018 at 01:26:09PM +0300, Amir Goldstein wrote: >>>>> Currently, there is a small window where ovl_obtain_alias() can >>>>> race with ovl_instantiate() and create two different overlay inodes >>>>> with the same underlying real non-dir non-hardlink inode. >>>>> >>>>> The race requires an adversary to guess the file handle of the >>>>> yet to be created upper inode and decode the guessed file handle >>>>> after ovl_creat_real(), but before ovl_instantiate(). >>>>> >>>>> This patch fixes the race, by using insert_inode_locked4() to add >>>>> a newly created inode to icache. >>>>> >>>>> If the newly created inode apears to already exist in icache (hashed >>>>> by the same real upper inode), we export this error to user instead >>>>> of silently not hashing the new inode. >>>> >>>> So we might return an error to user saying operation failed, but still >>>> create file on upper. Does that sound little odd? >>>> >>> >>> Yes, but I don't see a better solution. >> >> Might be better to kick the other, offending inode out, instead of >> returning an error. It would also simplify the error handling. >> >> We can do that by creating an ovl_inode_test_kick() variant that >> unhashes the inode on match. Also needs insert_inode_locked4() to use >> hlist_for_each_entry_safe() instead of hlist_for_each_entry(). >> > > Do you really think that this corner use case calls for such actions, > as creating flavors of inode cache helpers? Yes, if it simplifies error handling. > Remember that the so called "offending" inode, is not offending in > a way that is wrong or incomplete in any way. Right, so what about just using that inode instead of erroring out? Thanks, Miklos