On Fri, Jul 18, 2014 at 03:21:49PM -0400, J. Bruce Fields wrote:
> On Fri, Jul 18, 2014 at 03:04:04PM -0400, Jeff Layton wrote:
> > On Fri, 18 Jul 2014 13:49:57 -0400
> > "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> >
> > > On Fri, Jul 18, 2014 at 01:31:40PM -0400, Jeff Layton wrote:
> > > > On Fri, 18 Jul 2014 12:28:25 -0400
> > > > "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> > > >
> > > > > On Fri, Jul 18, 2014 at 11:13:27AM -0400, Jeff Layton wrote:
> > > > > > Move more of the delegation fields to be protected by the fi_lock. It's
> > > > > > more granular than the state_lock and in later patches we'll want to
> > > > > > be able to rely on it in addition to the state_lock.
> > > > > >
> > > > > > Also, the current code in nfs4_setlease calls vfs_setlease and uses the
> > > > > > client_mutex to ensure that it doesn't disappear before we can hash the
> > > > > > delegation. With the client_mutex gone, we'll have a potential race
> > > > > > condition.
> > > > > >
> > > > > > It's possible that the delegation could be recalled after we acquire the
> > > > > > lease but before we ever get around to hashing it. If that happens, then
> > > > > > we'd have a nfs4_file that *thinks* it has a delegation, when it
> > > > > > actually has none.
> > > > >
> > > > > I understand now, thanks: so the lease break code walks the list of
> > > > > delegations associated with the file, finds none, and issues no recall,
> > > > > but the open code continues merrily on and returns a delegation, with
> > > > > the result that we return the client a delegation that will never be
> > > > > recalled.
> > > > >
> > > > > That could be worded more carefully, and would be worth a separate patch
> > > > > (since the bug predates the new locking).
> > > > >
> > > >
> > > > Yes, that's basically correct. I'd have to think about how to fix that
> > > > with the current code. It's probably doable if you think it's
> > > > worthwhile, but I'll need to rebase this set on top of it.
> > >
> > > Well, I was wondering if this patch could just be split in two, no need
> > > to backport further than that.
> > >
> >
> > Erm, now that I've looked, I don't think it'll be that easy. The key
> > here is to ensure that fi_had_conflict is set while holding the
> > fi_lock. The trick here is that we need to take it in nfs4_setlease as
> > well, and check the flag before hashing the delegation without dropping
> > the fi_lock.
>
> OK, I'll live. For the sake of anyone that actually runs across that
> bug I'll update the summary and changelog to emphasize the bugfix over
> the locking change.
So, intending to apply as follows.
--b.
commit 417c6629b2d81d5a18d29c4bbb6a9a4c64282a36
Author: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
Date: Mon Jul 21 09:34:57 2014 -0400
nfsd: fix race that grants unrecallable delegation
If nfs4_setlease succesfully acquires a new delegation, then another
task breaks the delegation before we reach hash_delegation_locked, then
the breaking task will see an empty fi_delegations list and do nothing.
The client will receive an open reply incorrectly granting a delegation
and will never receive a recall.
Move more of the delegation fields to be protected by the fi_lock. It's
more granular than the state_lock and in later patches we'll want to
be able to rely on it in addition to the state_lock.
Attempt to acquire a delegation. If that succeeds, take the spinlocks
and then check to see if the file has had a conflict show up since then.
If it has, then we assume that the lease is no longer valid and that
we shouldn't hand out a delegation.
There's also one more potential (but very unlikely) problem. If the
lease is broken before the delegation is hashed, then it could leak.
In the event that the fi_delegations list is empty, reset the
fl_break_time to jiffies so that it's cleaned up ASAP by
the normal lease handling code.
Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 10cdb67..cc477dd 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -624,6 +624,8 @@ nfs4_put_delegation(struct nfs4_delegation *dp)
static void nfs4_put_deleg_lease(struct nfs4_file *fp)
{
+ lockdep_assert_held(&state_lock);
+
if (!fp->fi_lease)
return;
if (atomic_dec_and_test(&fp->fi_delegees)) {
@@ -643,11 +645,10 @@ static void
hash_delegation_locked(struct nfs4_delegation *dp, struct nfs4_file *fp)
{
lockdep_assert_held(&state_lock);
+ lockdep_assert_held(&fp->fi_lock);
dp->dl_stid.sc_type = NFS4_DELEG_STID;
- spin_lock(&fp->fi_lock);
list_add(&dp->dl_perfile, &fp->fi_delegations);
- spin_unlock(&fp->fi_lock);
list_add(&dp->dl_perclnt, &dp->dl_stid.sc_client->cl_delegations);
}
@@ -659,17 +660,18 @@ unhash_delegation(struct nfs4_delegation *dp)
spin_lock(&state_lock);
dp->dl_stid.sc_type = NFS4_CLOSED_DELEG_STID;
+ spin_lock(&fp->fi_lock);
list_del_init(&dp->dl_perclnt);
list_del_init(&dp->dl_recall_lru);
- spin_lock(&fp->fi_lock);
list_del_init(&dp->dl_perfile);
spin_unlock(&fp->fi_lock);
- spin_unlock(&state_lock);
if (fp) {
nfs4_put_deleg_lease(fp);
- put_nfs4_file(fp);
dp->dl_file = NULL;
}
+ spin_unlock(&state_lock);
+ if (fp)
+ put_nfs4_file(fp);
}
static void destroy_revoked_delegation(struct nfs4_delegation *dp)
@@ -3141,10 +3143,19 @@ static void nfsd_break_deleg_cb(struct file_lock *fl)
*/
fl->fl_break_time = 0;
- fp->fi_had_conflict = true;
spin_lock(&fp->fi_lock);
- list_for_each_entry(dp, &fp->fi_delegations, dl_perfile)
- nfsd_break_one_deleg(dp);
+ fp->fi_had_conflict = true;
+ /*
+ * If there are no delegations on the list, then we can't count on this
+ * lease ever being cleaned up. Set the fl_break_time to jiffies so that
+ * time_out_leases will do it ASAP. The fact that fi_had_conflict is now
+ * true should keep any new delegations from being hashed.
+ */
+ if (list_empty(&fp->fi_delegations))
+ fl->fl_break_time = jiffies;
+ else
+ list_for_each_entry(dp, &fp->fi_delegations, dl_perfile)
+ nfsd_break_one_deleg(dp);
spin_unlock(&fp->fi_lock);
}
@@ -3491,46 +3502,77 @@ static int nfs4_setlease(struct nfs4_delegation *dp)
{
struct nfs4_file *fp = dp->dl_file;
struct file_lock *fl;
- int status;
+ struct file *filp;
+ int status = 0;
fl = nfs4_alloc_init_lease(fp, NFS4_OPEN_DELEGATE_READ);
if (!fl)
return -ENOMEM;
- fl->fl_file = find_readable_file(fp);
- status = vfs_setlease(fl->fl_file, fl->fl_type, &fl);
- if (status)
- goto out_free;
+ filp = find_readable_file(fp);
+ if (!filp) {
+ /* We should always have a readable file here */
+ WARN_ON_ONCE(1);
+ return -EBADF;
+ }
+ fl->fl_file = filp;
+ status = vfs_setlease(filp, fl->fl_type, &fl);
+ if (status) {
+ locks_free_lock(fl);
+ goto out_fput;
+ }
+ spin_lock(&state_lock);
+ spin_lock(&fp->fi_lock);
+ /* Did the lease get broken before we took the lock? */
+ status = -EAGAIN;
+ if (fp->fi_had_conflict)
+ goto out_unlock;
+ /* Race breaker */
+ if (fp->fi_lease) {
+ status = 0;
+ atomic_inc(&fp->fi_delegees);
+ hash_delegation_locked(dp, fp);
+ goto out_unlock;
+ }
fp->fi_lease = fl;
- fp->fi_deleg_file = fl->fl_file;
+ fp->fi_deleg_file = filp;
atomic_set(&fp->fi_delegees, 1);
- spin_lock(&state_lock);
hash_delegation_locked(dp, fp);
+ spin_unlock(&fp->fi_lock);
spin_unlock(&state_lock);
return 0;
-out_free:
- if (fl->fl_file)
- fput(fl->fl_file);
- locks_free_lock(fl);
+out_unlock:
+ spin_unlock(&fp->fi_lock);
+ spin_unlock(&state_lock);
+out_fput:
+ fput(filp);
return status;
}
static int nfs4_set_delegation(struct nfs4_delegation *dp, struct nfs4_file *fp)
{
+ int status = 0;
+
if (fp->fi_had_conflict)
return -EAGAIN;
get_nfs4_file(fp);
+ spin_lock(&state_lock);
+ spin_lock(&fp->fi_lock);
dp->dl_file = fp;
- if (!fp->fi_lease)
+ if (!fp->fi_lease) {
+ spin_unlock(&fp->fi_lock);
+ spin_unlock(&state_lock);
return nfs4_setlease(dp);
- spin_lock(&state_lock);
+ }
atomic_inc(&fp->fi_delegees);
if (fp->fi_had_conflict) {
- spin_unlock(&state_lock);
- return -EAGAIN;
+ status = -EAGAIN;
+ goto out_unlock;
}
hash_delegation_locked(dp, fp);
+out_unlock:
+ spin_unlock(&fp->fi_lock);
spin_unlock(&state_lock);
- return 0;
+ return status;
}
static void nfsd4_open_deleg_none_ext(struct nfsd4_open *open, int status)
--
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