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? Thanks, Miklos
