On Sat, Dec 24, 2011 at 10:55:25PM +0000, Al Viro wrote:
> On Sat, Dec 24, 2011 at 04:50:12PM -0500, J. Bruce Fields wrote:
>
> > locks: fix null dereference on lease-break failure path
> >
> > Commit 778fc546f749c588aa2f6cd50215d2715c374252 "locks: fix tracking of
> > inprogress lease breaks" introduced a null dereference on failure to
> > allocate memory.
> >
> > This means an open (without O_NONBLOCK set) on a file with a lease
> > applied (generally only done when Samba or nfsd (with v4) is running)
> > could crash if a kmalloc() fails.
>
> NULL? AFAICS, lease_alloc() returns ERR_PTR() on failure...
Erp, you're right.
(The fix is still right, it's the changelog that's wrong; happy to
fix and resend if it's wanted....)
> I really
> don't like the look of that code, TBH - at the very least it needs to
> be commented a lot. E.g. the rules for calling or not calling ->lm_break()
> are really not obvious - AFAICS, we do that if
> i_have_this_lease || (mode & O_NONBLOCK)
> is true *or* if allocation has succeeded. The former condition is what'll
> end up with -EWOULDBLOCK; I can understand not wanting to return that in
> preference to -ENOMEM, but... Do we want to skip ->lm_break() stuff only
> in case of allocation failures that won't be overridden by -EWOULDBLOCK?
We do want to break leases at least in the O_NONBLOCK case so that a
caller can make forward progress by retrying open(.,O_NONBLOCK).
In the other cases I don't think there's any logic to the current
behavior. Something like:
- if (IS_ERR(new_fl) && !i_have_this_lease
- && ((mode & O_NONBLOCK) == 0)) {
- error = PTR_ERR(new_fl);
- goto out;
- }
-
...
error = -EWOULDBLOCK;
goto out;
}
-
+ if (IS_ERR(new_fl)) {
+ error = PTR_ERR(new_fl);
+ goto out;
+ }
restart:
break_time = flock->fl_break_time;
if (break_time != 0) {
would be a little less convoluted.
Or we could just do it the really obvious way:
new_fl = lease_alloc(NULL, want_write ? F_WRLCK : F_RDLCK);
+ if (IS_ERR(new_fl))
+ return PTR_ERR(new_fl);
lock_flocks();
...
- if (IS_ERR(new_fl) && !i_have_this_lease
- && ((mode & O_NONBLOCK) == 0)) {
- error = PTR_ERR(new_fl);
- goto out;
- }
-
Then you're returning -ENOMEM in a case when we really didn't need to do
an allocation, but is that really a problem? It's a rare case, and
opens can already fail with -ENOMEM for other reasons, and I'd rather
not have the extra hair.
?
--b.
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