On Wed, May 16, 2018 at 1:14 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > On Wed, May 16, 2018 at 11:51 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: >> On Wed, May 16, 2018 at 11:34 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: >>> On Tue, May 15, 2018 at 3:37 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: >>>> On Tue, May 15, 2018 at 4:23 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> 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? > OK. I'll see what comes out. Thanks, Amir.
