On Wed, Jan 21, 2009 at 12:23:09PM +0000, David Howells wrote: > J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > > - Finally, we put_cred(override_creds(new)). That modifies > > current->cred again, putting the old value and getting the > > new. > > > > Hm. But that last part's not OK; aren't we still holding our own > > reference to new, in addition to the one that override_creds() just > > took? So I think we need the following? > > Yes, you're right. override_creds() takes an extra ref on the argument it is > passed, thus leaving the caller with their original reference intact. > > So really, you don't want to call override_creds() as that will cost you an > extra atomic_inc() and atomic_dec_and_test(). I recommend you replace: > > put_cred(override_creds(new)); > > with: > > revert_creds(new); > > I think that should do the right thing. It may look a bit odd, but it'll be > quicker. If you object to using revert_creds)( because of the name, we can > come up with an alternative name. If the only difference is just whether it takes a reference on the passed-in cred it might be clearest just to write set_creds(new); or set_creds(get_creds(new)); depending on which you want? In any case, yes, the revert_creds()/override_creds() names don't tell me much. > > Looking through nfsd_setuser(), one obvious bug: in the (flags & > > NFSEXP_ALLSQUASH) case, we never check the return value from the > > groups_alloc(0). If it returns NULL, we dereference it anyway. > > Since a zero-length groups list must be copied before writing, can I recommend > that we make groups_alloc(0) a special case that returns pointer to a > statically allocated groups list (after inc'ing the refcount) that represents > a zero-length list, thus meaning groups_alloc(0) will never fail? Is there a really big advantage to that? On the face of it it strikes me as a weird corner case that I'll trip over every time I look at this code. --b. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
